Internal combustion engine system, vehicle and method for controlling the geometric compression ratio of a reciprocating compressor of an internal combustion engine system

Abstract

The present disclosure relates to an internal combustion engine system (100) comprising a reciprocating compressor (120) for pressurizing a fluid medium and having a compressor cylinder (121) for accommodating a compressor piston (122), the compressor cylinder having a primary cylinder volume (124) and a secondary adjustable volume (126), the secondary adjustable volume (126) being in fluid communication with the primary cylinder volume to provide a variable geometric compression ratio.

Description

Technical Field

[0001] The present disclosure relates to an internal combustion engine system, which includes a reciprocating compressor for pressurizing a fluid medium. The present disclosure is applicable to vehicles, in particular heavy vehicles such as trucks. However, although the present disclosure will be described primarily with respect to trucks, the internal combustion engine system may also be applicable to other types of vehicles propelled by an internal combustion engine. In particular, the present disclosure may be applied to heavy vehicles, such as trucks, buses, and construction equipment, but may also be applied to cars and other light vehicles, etc. In addition, the internal combustion engine is typically a hydrogen internal combustion engine. Background Art

[0002] The demand for internal combustion engines has been growing steadily over the years, and engines have been continuously developed to meet the various needs of the market. For example, reducing exhaust gases, improving engine efficiency (i.e., reducing fuel consumption) and reducing engine noise levels are some of the criteria that have become more important when designing and selecting suitable internal combustion engine (ICE) systems and their engine components. Furthermore, in the field of heavy-duty vehicles (e.g., trucks), there are many current environmental regulations that set specific requirements for vehicles, such as restrictions related to the maximum allowed amount of exhaust gas pollution.

[0003] In order to meet at least some of the above requirements, various engine concepts have been developed over the years in which a conventional combustion cylinder, for example, has been combined with a pre-compression stage and / or an expansion stage.

[0004] One type of ICE system that has the potential to meet current and future environmental regulations is a hydrogen ICE system, in which the combustion of hydrogen with oxygen produces water as its only product. In such a hydrogen ICE system, there is typically a compressor that is used to pressurize the air before it enters the combustion cylinder, thereby providing the appropriate hydrogen and air mixture in the combustion cylinder when the combustion reaction is performed and completed. However, compressors are also often used in other types of ICE systems, such as more traditional diesel-type ICE systems.

[0005] It may be desirable to further improve the operation of the compressor in an ICE system. Summary of the invention

[0006] An object of the present invention is to provide an improved operation of a compressor for an internal combustion engine system, wherein the compressor can be operated more efficiently in relation to variations in engine load of the ICE system. This object is at least partly achieved by a system according to a first aspect of the present disclosure.

[0007] According to a first aspect of the present disclosure, an internal combustion engine (ICE) system is provided, the internal combustion engine system comprising a reciprocating compressor for pressurizing a fluid medium. The reciprocating compressor comprises a compressor cylinder for accommodating a compressor piston. In addition, the compressor cylinder has a main cylinder volume and a secondary adjustable volume, the secondary adjustable volume being in fluid communication with the main cylinder volume to provide a variable geometric compression ratio.

[0008] By providing a compressor with a secondary adjustable volume, the geometric compression ratio can be adjusted in response to demand from the ICE system. In addition, by providing a compressor with a variable geometric compression ratio, the size of the compressor in the ICE system can be reduced, at least to some extent. To this end, the present disclosure can have a positive impact not only on the potential for reducing the size of the ICE system due to more efficient compressor operation, but can also have a positive impact on the overall manufacturing cost of the ICE system.

[0009] Although the present disclosure can be used for any type of ICE system including a piston compressor for compressing a fluid medium, the present disclosure is particularly applicable to a hydrogen internal combustion system. Therefore, according to at least one embodiment, the ICE system is a hydrogen ICE system. In this hydrogen ICE system, the combustion of hydrogen and oxygen produces water as its only product. In addition, hydrogen can be burned in an internal combustion engine through various fuel-air mixtures. Although the hydrogen ICE system can operate under certain conditions and produce very low emissions, the NOx emissions may still depend at least in part on the air / fuel ratio, the engine geometric compression ratio, and the engine speed and ignition timing. In addition, compared with, for example, a traditional gasoline engine, the combustion of air / fuel in a hydrogen ICE system may place higher requirements on the strength and size of engine components.

[0010] Typically, the reciprocating compressor is configured to compress air by displacement of the compressor piston from the bottom dead center (BDC) to the top dead center (TDC). In addition, the primary cylinder volume is typically defined as a first space for compressed air. Similarly, the secondary adjustable volume can be considered to define an additional space for compressed air. In this way, the secondary adjustable volume is used to adjust the total volume of the reciprocating compressor (i.e., the internal space defined by the first space and the additional space). In this way, a variable compression ratio can be provided during operation of the reciprocating compressor and the ICE system.

[0011] By providing variable geometric compression ratio control, the present invention allows adjustment of the dead volume of the compressor, ie, the relationship between the internal volume of the compressor when the piston is at top dead center (TDC) and the internal volume of the compressor when the piston is at bottom dead center (BDC).

[0012] Typically, the secondary adjustable volume provides an increased "dead volume" for the compressor. The dead volume may typically be equal to the volume of the compressor when the piston is at top dead center (TDC). In other words, the dead volume may be the volume defined by the total volume of the compressor minus the swept volume. The dead volume may also be referred to as the clearance volume or collision clearance. The construction of the compressor may be provided in several different ways. Typically, the secondary adjustable volume is provided by a compartment arrangement. The compartment may include a plurality of sub-compartments defining a plurality of sub-volumes. In this way, the secondary adjustable volume can be adjusted by the number of sub-compartments, i.e., the sub-compartments provide different dead volumes.

[0013] Additionally or alternatively, the secondary adjustable volume is provided by a compartment configured to be adjustable in size. Similarly, in examples where the secondary adjustable volume is defined by a plurality of sub-compartments, each sub-compartment may also be adjustable in size, ie, adjustable in volume.

[0014] According to at least one embodiment, the secondary adjustable volume is configured to provide geometric compression ratio control of the compressor cylinder by adjusting the volume of the secondary adjustable volume to a plurality of defined volumes. Typically, the secondary adjustable volume comprises at least a plurality of volume compartment portions.

[0015] According to at least one embodiment, the secondary adjustable volume comprises at least a plurality of volume compartment parts of different sizes. In this way, a more stepless control of the adjustable volume can be provided. In addition, the use of volume parts of different sizes increases the number of possible volume combinations of the adjustable volume.

[0016] According to at least one embodiment, the secondary adjustable volume comprises at least a plurality of fixed-sized volume compartment portions.By having a plurality of fixed-sized volume portions, a simpler arrangement of the adjustable volume is provided.

[0017] According to at least one embodiment, the total dead volume is provided by at least two volume compartment portions of equal size.

[0018] According to at least one embodiment, the total dead volume is provided by at least two volume compartment portions of different sizes.

[0019] For example, each of the two volume compartment parts of different sizes is arranged to be in fluid communication with the main cylinder volume via at least one valve. By connecting the two volume compartment parts to the main volume of the compressor cylinder via the valve, four different geometric compression ratios can be provided. That is, different geometric compression ratios can be obtained by controlling the opening of the valve. In this way, a secondary adjustable volume with four different dead volume controls (i.e., providing four different geometric compression ratios) is provided.

[0020] The at least one valve may be a rotatable valve assembly arranged to open and close the inlets to at least two volume compartment portions of different sizes respectively by rotation of the rotatable valve about its central axis. By controlling the valve, the two compartments may be placed in fluid communication with the main cylinder volume of the compressor.

[0021] In another example embodiment, each of the two volume compartment portions is arranged in fluid communication with the master cylinder volume via a first valve and a second valve, respectively.

[0022] In addition, for different compressor configurations, the valve may be different. For example, the type of the valve may be selected from a poppet valve, a rotary valve, a reed valve, a slide valve or any other suitable valve.

[0023] In the example where the valve is a slide valve, the slide valve is arranged between the primary cylinder volume and the secondary adjustable volume, wherein the slide valve is arranged to be pressed against the opening of the secondary adjustable volume by the compression pressure in the compressor cylinder. In this example, the slide valve performs a displacement from the closed position to the open position when the pressure in the compressor cylinder is at atmospheric pressure during the compressor intake stroke. In this way, losses and wear can be reduced. Furthermore, an ICE system with at least one valve can be provided, which allows the use of a less powerful valve actuator compared to a more complex valve.

[0024] Typically, the fluid medium to be compressed by the compressor is air (oxygen). Therefore, the reciprocating compressor may typically include an inlet for ambient air and an outlet for compressed air. The inlet may include an inlet valve for regulating the inflow of air into the compressor, and the outlet may include an outlet valve for regulating the outflow of compressed air from the compressor, as is well known in the art. During air compression, the inlet and outlet are typically closed.

[0025] Typically, the reciprocating compressor can be operated by the crankshaft of the internal combustion engine.

[0026] Typically, the compressor cylinder is configured to compress a volume of air and deliver the compressed air to at least one combustion piston of the ICE system. In this type of configuration of the present disclosure, the (dead) volume of the secondary adjustable volume is adjusted so as to adjust the geometric compression ratio of the compressor to obtain a desired air flow into the combustion cylinder of the ICE system.

[0027] According to at least one embodiment, the volume of the secondary adjustable volume is adjusted in response to the engine load of the ICE system. By adjusting the volume of the secondary adjustable volume in response to the engine load of the ICE system, the compressor can be operated in a more efficient manner by adjusting the geometric compression ratio based on the load on the ICE. To this end, the flow of fresh air and exhaust gas recirculation (EGR) pumped through the ICE system can be adjusted. In general, each engine load / rpm point can have target values ​​for fresh air and EGR flow.

[0028] In particular, by adjusting the dead volume (via the secondary adjustable volume) in response to the load on the engine, not only can a more efficient compressor be provided due to the ability to adjust the dead volume in response to the engine load, but pumping losses and friction at low loads can also be reduced. That is, the present disclosure allows the compressor to be operated at a lower geometric compression ratio at low loads. In this way, the compressor rate can be reduced.

[0029] The engine load of the ICE system can be determined in several different ways. The engine load is usually determined by a control unit, such as an ECU of the ICE system or vehicle. For example, the engine load of the ICE system can be determined based on the actuation of the vehicle accelerator (e.g., an accelerator pedal). The requested propulsion torque can be determined, for example, based on the position of the accelerator pedal manipulated by the driver. In addition or alternatively, the engine load of the ICE system can be determined by a control unit (e.g., an electronic control unit) based on data indicating the requested propulsion torque. As used herein, the term "requested propulsion torque" generally refers to the propulsion torque required by the vehicle in the current state, that is, the torque that can be delivered by the internal combustion engine according to the request of the driver, control unit, etc. Typically, a specific torque request results in a specific setting of the actuator in the ICE. In addition, the ICE system may include one or more sensors for collecting relevant data, such as a pressure sensor in an expander, or at least a pressure sensor in a cold tank between a compressor and a combustion cylinder, so as to more accurately determine the impact of the specific torque request. The relevant data collected from the ICE system can be transmitted to the control unit of the ICE system or the vehicle. Therefore, the pressure sensor can generally be arranged to communicate with the control unit of the ICE system or the vehicle.

[0030] According to at least one embodiment, the ICE system is operable to adjust the secondary adjustable volume by opening / closing a passage between the primary volume and the secondary adjustable volume. Typically, the ICE system is operable to adjust the secondary adjustable volume by opening / closing a passage between the primary cylinder volume and the secondary adjustable volume when the pressure in the primary cylinder volume is substantially similar to the pressure in the secondary adjustable volume.

[0031] According to at least one embodiment, the ICE system is operable to detect the position of the compressor piston in the compressor cylinder. Typically, the position of the compressor piston can be determined by a flywheel position sensor, as is conventionally used in the field of ICE systems. To this end, the volume of the secondary adjustable volume can typically be adjusted in response to the detected position of the compressor piston in the compressor cylinder so as to adjust the volume of the secondary adjustable volume based on the engine load. The flywheel position sensor can be arranged to communicate with a control unit of the ICE system and / or the vehicle.

[0032] According to at least one embodiment, the ICE system is operable such that during the compression stroke, the fluid communication between the master cylinder and the secondary adjustable volume is always open. In particular, the fluid communication between the master cylinder and the secondary adjustable volume is open during the compression stroke and until the engine load in the ICE system changes. In this way, a certain dead volume is always open during the compression stroke until the demand for air decreases or increases due to changes in engine load.

[0033] According to at least one embodiment, the ICE system comprises a control unit for controlling the secondary adjustable volume.

[0034] The control unit may include a microprocessor, a microcontroller, a programmable digital signal processor or another programmable device. Therefore, the control unit generally includes electronic circuits and connections and processing circuits so that the control unit can communicate with different parts of the ICE system (e.g., ICE, compressor, expander) or with any other components of the vehicle (e.g., clutch) and / or any other components that need to be operated to provide the functions of the example embodiment. Generally, the control unit can also be configured to communicate with other components of the vehicle, such as brakes, suspensions, and other electrical auxiliary devices such as air conditioning systems, so as to at least partially operate the vehicle. The control unit may include hardware or software modules, or modules of part of the hardware or software, and communicate using known transmission buses such as CAN buses and / or wireless communication capabilities. The processing circuit may be a general-purpose processor or a dedicated processor. The control unit generally includes a non-transient memory for storing computer program code and data thereon. Therefore, the control unit can be implemented by many different configurations.

[0035] In other words, the control functions of the example embodiments of the ICE system can be implemented using an existing computer processor, or by a dedicated computer processor for an appropriate system (for this purpose or other purposes included), or by a hard-wired system. Embodiments within the scope of the present disclosure include program products, which include machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available medium that can be accessed by a general or special-purpose computer or other machine with a processor. For example, such computer-readable media can include RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage device or any other medium, which can be used to carry or store the desired program code in the form of machine-executable instructions or data structures and can be accessed by a general or special-purpose computer or other machine with a processor. When information is transmitted or provided to a machine via a network or other communication connection (hardwired, wireless, or a combination of hardwired or wireless), the machine appropriately regards the connection as a machine-readable medium. Therefore, any such connection is appropriately referred to as a machine-readable medium. The above combination is also included in the scope of machine-readable media. Machine executable instructions include, for example, instructions and data that cause a general purpose computer, a special purpose computer, or a special purpose processing machine to perform a function or a group of functions. Although the example embodiments of the above-described system include a control unit as an integral part thereof, the control unit may also be a separate part of the vehicle and / or be arranged remotely from and in communication with the system.

[0036] Although the present disclosure can be used for any type of ICE system including a reciprocating compressor, the present disclosure is particularly applicable to an ICE system including an expander and a combustion cylinder. Therefore, the ICE system can generally include at least one combustion cylinder configured to cause a gaseous fuel to burn in a combustion chamber of the combustion cylinder assembly, thereby driving a crankshaft.

[0037] Therefore, according to at least one embodiment, the ICE system also includes at least one combustion cylinder, which accommodates a combustion piston. The combustion cylinder is configured to be powered by combustion force. In addition, the compressor cylinder is configured to compress a certain volume of air and transmit the compressed air to at least one combustion piston. In addition, the ICE system includes an expander cylinder, which accommodates an expander piston. The expander cylinder is configured to receive exhaust gas from at least one combustion piston. In addition, the ICE system includes a crankshaft, which can be connected to at least one combustion piston and to at least one of the expander piston and the compressor piston through a corresponding connecting rod.

[0038] For example, the crankshaft is driven by at least one combustion piston via a combustion piston connecting rod and is also driven by an expander piston via an expander piston connecting rod, while the compressor piston is driven by the crankshaft via the expander piston. That is, the crankshaft is connected to at least one combustion piston and the expander piston via respective connecting rods. In other words, the expander piston connecting rod converts the reciprocating motion of the compressor piston and the expander piston into a rotational motion of the crankshaft.

[0039] Alternatively, the crankshaft is connected to at least one combustion piston via a connecting rod and is also connected to a compressor piston via a connecting rod, while the expander piston is connected to the crankshaft via a connecting element assembly extending between the compressor piston and the expander piston.

[0040] Thus, according to one embodiment, the crankshaft is driven by at least one combustion piston via a combustion piston connecting rod and by an expander piston via an expander piston connecting rod, wherein the compressor piston is driven by the crankshaft via the expander piston.

[0041] Typically, the crankshaft is driven, i.e. receives power from the combustion cylinder and the combustion piston due to the combustion force, and receives power from the expander cylinder and the expander piston due to the expansion force. In addition, the crankshaft drives the compressor piston and the compressor cylinder (i.e. delivers power to the compressor piston and the compressor cylinder) to compress the air. Therefore, the crankshaft can be rotationally driven by the power piston (i.e. at least by the at least one combustion piston and the expander piston) through a connecting rod, and the crankshaft drives the power-consuming piston (i.e. at least the compressor piston) through the connecting rod that already exists and is used for the power piston. In other words, and according to one embodiment, the ICE system includes a connecting rod that is directly connected only to the power piston (i.e., the at least one combustion piston and the expander piston).

[0042] By way of example, the crankshaft is driven by at least one combustion piston via a combustion piston connecting rod and by an expander piston via an expander piston connecting rod, wherein the compressor piston is driven by the crankshaft via the expander piston.

[0043] It will be appreciated that at least one combustion piston is disposed within the at least one combustion cylinder and is adapted to reciprocate therein. Accordingly, the compressor piston and the expander piston are disposed within the compressor cylinder and the expander cylinder, respectively, and are adapted to reciprocate therein.

[0044] Furthermore, a "downward" stroke of the compressor piston refers to a stroke during which the air in the compressor cylinder is compressed. Accordingly, an "upward" stroke of the compressor piston refers to a stroke of the compressor piston in the opposite direction.

[0045] Furthermore, the expander piston may typically be rigidly connected to the compressor piston to allow the expander piston to move in unison with the compressor piston. In this configuration, the downward and upward strokes of the compressor piston coincide with the corresponding strokes of the expander piston.

[0046] According to at least one embodiment, the compressor piston is connected to the crankshaft via the expander piston, such that a rotational motion of the crankshaft is converted into a reciprocating motion of the compressor piston via the expander piston connecting rod.

[0047] Therefore, according to at least one embodiment, the expander piston and the compressor piston are arranged with a common connecting rod. That is, the compressor piston is connected to the crankshaft via the expander piston connecting rod.

[0048] In other words, the crankshaft is driven by at least one combustion piston via its connecting rod (ie, combustion piston connecting rod) and by the expander piston via its connecting rod (ie, expander piston connecting rod).

[0049] According to at least one embodiment, the internal combustion engine further comprises a connecting element assembly, which rigidly connects the compressor piston and the expander piston so that the compressor piston and the expander piston can move in unison. Through the connecting element assembly, a mechanical rigid connection is provided between the expander piston and the compressor piston, thereby improving the mechanical stability of the internal combustion engine. Since the expander piston and the compressor piston are rigidly connected to each other, the total height of the expander piston and the compressor piston can be lower compared to a design in which the expander piston and the compressor piston are not rigidly connected to each other. In addition, since the expander piston is rigidly connected to the compressor piston by the connecting element assembly and therefore moves in unison with the compressor piston, the downward and upward strokes of the compressor piston coincide with the corresponding strokes of the expander piston.

[0050] According to one embodiment, the compressor piston, the expander piston and a portion of the crankshaft are arranged along a geometric axis, and wherein a portion of the crankshaft is arranged along the geometric axis between the compressor piston and the expander piston. Thus, a more compact design of the internal combustion engine can be achieved. The portion of the crankshaft can be described as a middle portion of the expander piston and the compressor piston, and the portion of the crankshaft can be, for example, a section of the crankshaft along the longitudinal direction of the crankshaft.

[0051] According to one embodiment, the reciprocating motion of the expander piston in the expander cylinder occurs along the expander axis and the reciprocating motion of the at least one combustion piston in the combustion cylinder occurs along the combustion axis. According to one embodiment, the geometrical axis coincides with the expander axis and the compressor axis.

[0052] According to one embodiment, the compressor piston, the expander piston and a portion of the crankshaft are arranged in a geometric plane that extends along at least one of the expander axis and the compressor axis and is perpendicular to the longitudinal axis of the crankshaft, wherein a portion of the crankshaft is arranged in the geometric plane between the compressor piston and the expander piston in a direction perpendicular to the longitudinal axis of the crankshaft.

[0053] According to one embodiment, at least a portion of the compressor piston, at least a portion of the expander piston and at least a portion of the connecting element assembly together form a compressor-expander arrangement around a portion of the crankshaft. According to one embodiment, the compressor-expander device encloses or surrounds a portion of the crankshaft. Thus, a compact design of an internal combustion engine system can be achieved.

[0054] According to one embodiment, the expander cylinder and the compressor cylinder are coaxially arranged. Therefore, alignment of the expander cylinder and the compressor cylinder within the respective cylinders is facilitated. According to one embodiment, the crankshaft is closer to the compressor cylinder than to the expander cylinder. According to one embodiment, the combustion piston connecting rod is coupled to the crankshaft (i.e., the large end of the connecting rod) on the same crankshaft side as the expander connecting rod, opposite to the compressor piston. Therefore, the risk of collision of internal components is reduced. Therefore, a more compact design of the ICE system can be achieved.

[0055] According to one embodiment, the expander cylinder and the compressor cylinder are offset from each other. That is, the expander axis and the compressor axis are parallel to each other but do not coincide.

[0056] According to one embodiment, the expander cylinder and the at least one combustion cylinder are arranged in the internal combustion engine so that the expander axis is inclined between 40 and 90 degrees relative to the combustion axis, preferably between 50 and 75 degrees, more preferably between 55 and 65 degrees, for example about 60 degrees.

[0057] Thus, the internal components (e.g. the various pistons and corresponding connecting rods) can be adapted to remain non-interfering with each other as these components move within the internal combustion engine while performing their reciprocating and / or rotational motion. Thus, the internal combustion engine system can be made more compact. Thus, the at least one combustion cylinder can be described as protruding laterally from the crankshaft compared to the expander cylinder.

[0058] According to one embodiment, the expander piston connecting rod and the combustion piston connecting rod are coupled to the crankshaft via respective crankpins. Thus, the expander piston and the at least one combustion piston can be individually phased relative to each other with respect to the crankshaft. Thus, a uniform distribution of torque pulses can be achieved. According to one embodiment, the expander piston connecting rod and the combustion piston connecting rod are coupled to the crankshaft via the same crankpin.

[0059] According to one embodiment, the expander piston is physically separated from the compressor piston by a connecting element. That is, the expander piston and the compressor piston are not a common piston, but two separate pistons rigidly connected by the connecting element. Therefore, the expander piston, the compressor piston and the connecting element can be referred to as a compressor-expander arrangement, wherein the two pistons are rigidly connected to each other by the connecting element. According to one embodiment, the expander piston, the compressor piston and the connecting element can be made into one piece and / or included in a single unit.

[0060] According to one embodiment, the at least one combustion cylinder is a first combustion cylinder and the combustion piston is a first combustion piston, and the internal combustion engine further comprises a second combustion cylinder accommodating a second combustion piston, the second combustion cylinder being configured to be powered by combustion forces.

[0061] Therefore, the at least one combustion cylinder may refer to at least two combustion cylinders. According to one embodiment, the second combustion piston is connected to the crankshaft via a connecting rod. That is, the first and second combustion pistons are connected to the same crankshaft.

[0062] It should be understood that according to one embodiment, the at least one combustion cylinder or at least two combustion cylinders are at least partially arranged between the expander piston and the compressor piston. For example, the connecting rod of the combustion cylinder can be arranged between the expander piston and the compressor piston.

[0063] According to one embodiment, the first combustion cylinder and the second combustion cylinder are operated in a four-stroke configuration, and each of the compressor cylinder and the expander cylinder are operated in a two-stroke configuration.

[0064] According to one embodiment, the first and second combustion cylinders operate together in a four-stroke configuration. According to one embodiment, the first and second combustion cylinders each operate in a two-stroke configuration. According to one embodiment, the first and second combustion cylinders each operate in a four-stroke configuration. Therefore, the total stroke of the ICE can be referred to as an eight-stroke engine (the respective two-stroke configurations of the expander cylinder and the compressor cylinder, and the four-stroke configuration of the combustion cylinder). According to one embodiment, the internal combustion engine is referred to as a dual compression expansion engine DCEE.

[0065] According to at least a second aspect of the present disclosure, the object is achieved by a vehicle. The vehicle comprises an internal combustion engine system according to the first aspect of the present disclosure.

[0066] The effects and features of this second aspect of the disclosure are largely similar to those described above in conjunction with the first aspect of the disclosure. The embodiments mentioned in relation to the first aspect of the disclosure are largely compatible with the second aspect of the disclosure.

[0067] According to a third aspect of the invention, there is provided a method for controlling a geometric compression ratio of a reciprocating compressor of an internal combustion engine (ICE) system. The reciprocating compressor is configured to pressurize a fluid medium and has a compressor cylinder for accommodating a compressor piston. The compressor cylinder has a main cylinder volume and a secondary adjustable volume, the secondary adjustable volume being in fluid communication with the main cylinder volume to provide a variable geometric compression ratio.

[0068] The method comprises the following steps: - adjusting the volume of the secondary adjustable volume to a first adjustable volume; and - pressurizing the fluid medium to a first geometric compression ratio by displacement of the compressor piston from bottom dead center (BDC) to top dead center (TDC).

[0069] The effects and features of the third aspect of the present disclosure are largely similar to those described above in conjunction with the first aspect of the present disclosure. The embodiments mentioned with respect to the first and second aspects of the present disclosure are largely compatible with the third aspect of the present disclosure.

[0070] According to at least one embodiment, the method further comprises the steps of: - determining an engine load of the ICE system; and - adjusting the volume of the secondary adjustable volume in response to the determined engine load.

[0071] The method according to the example embodiment can be performed in several different ways. According to an example embodiment, the steps of the method are performed by a control unit during use of the ICE system of the vehicle. According to an example embodiment, the steps of the method are performed sequentially. However, at least some steps of the method can be performed in parallel.

[0072] Other advantages and advantageous features of the present disclosure are disclosed in the following description.It should also be readily appreciated that different features may be combined to produce embodiments other than those described in the following, without departing from the scope of the present disclosure.

[0073] The terms used herein are only for the purpose of describing specific examples and are not intended to limit the present disclosure. As used herein, the singular forms "a", "an", and "the" are intended to include the plural as well, unless the context clearly indicates otherwise. It will be further understood that when used herein, the terms "include", "comprise", "have", and / or "contain" specify the presence of stated features, integers, steps, operations, elements, and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, and / or groups thereof.

[0074] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those commonly understood by those skilled in the art to which the present disclosure belongs. It should also be understood that the terms used herein should be interpreted as having the meaning consistent with their meaning in the context of this specification and the relevant field, and should not be interpreted in an idealized or overly formal sense unless explicitly defined in this article. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The above and other objects, features and advantages of the present disclosure will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments of the present disclosure, in which:

[0076] Figure 1 is a side view of a vehicle including an internal combustion engine (ICE) system according to an example embodiment of the present disclosure.

[0077] Figure 2 is a side view of a reciprocating compressor of an ICE system according to an example embodiment of the present disclosure.

[0078] Figure 3a to Figure 3f An exemplary embodiment according to the present disclosure is shown. Figure 2 Additional components for reciprocating compressors.

[0079] Figure 4 is a perspective view of an ICE system according to an example embodiment of the present disclosure.

[0080] Figure 5 is a flowchart of a method according to an exemplary embodiment of the present disclosure, wherein the method includes a plurality of steps for controlling Figure 1 The geometric compression ratio of the reciprocating compressor in the ICE system. DETAILED DESCRIPTION

[0081] The present disclosure will now be described more fully below with reference to the accompanying drawings showing exemplary embodiments of the present disclosure. However, the present disclosure may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided for sufficiency and completeness. Throughout the specification, the same reference numerals refer to the same elements.

[0082] Special reference Figure 1 , a vehicle 1 having an internal combustion engine (ICE) system 100 according to the present disclosure is provided. Figure 1 The vehicle 1 shown in FIG. 1 is a truck, and the internal combustion engine system 100 described in detail below is particularly suitable for use in such a truck. Figures 2 to 5As further described, the internal combustion engine system includes at least a reciprocating compressor. In addition, the internal combustion engine system 100 includes an internal combustion engine (ICE). In this example, the ICE system is a hydrogen piston internal combustion engine system. As is well known in the art, the combustion in such a hydrogen ICE system is based on the combustion of air and hydrogen.

[0083] like Figure 1 As shown in FIG. 1 , the ICE system generally further includes a control unit 180. Figure 5 As further described, the control unit 180 is configured to perform any of the steps of the method for controlling the reciprocating compressor of the ICE system. The control unit 180 is here part of a main electronic control unit for controlling the vehicle and various parts of the vehicle. In particular, the control unit 180 is arranged to communicate with the reciprocating compressor and other components of the ICE.

[0084] Now refer to Figure 2 as well as Figures 3a to 3f An example embodiment of a reciprocating compressor according to an example embodiment of the present disclosure will be described, and then reference will be made to Figure 4 To describe other components of the ICE system.

[0085] Steering Figure 2 , shows a reciprocating compressor 120 according to an exemplary embodiment of the present disclosure, the reciprocating compressor 120 is used in Figure 1 In the ICE system 100. Figure 2 As shown in , the reciprocating compressor 120 extends along a compression axis CA, which generally corresponds to the longitudinal direction of the reciprocating compressor 120. In this context, it should be noted that the term "cylinder" generally refers to a component having an internal space for accommodating a reciprocating piston, as is well known in the art. In addition, it should be noted that the reciprocating compressor may sometimes be denoted as a compressor.

[0086] The reciprocating compressor 120 includes a compressor cylinder 121 for accommodating a compressor piston 122. The compressor piston is connected to a connecting rod 154. Figure 4 As shown, the compressor piston connecting rod 154 connects the compressor piston 122 to the crankshaft 140. As is well known in the art, the compressor cylinder 120 is configured to extract a volume of ambient air, compress the air and deliver the compressed air to a suitable combustor of the ICE system. Figure 4 Further describing one example of a suitable burner arrangement, Figure 4 A combustor is depicted having a first combustion cylinder 111 and a second combustion cylinder 114 .

[0087] The reciprocating compressor is configured to compress air by displacement of the compressor piston from bottom dead center (BDC) to top dead center (TDC), as is well known in the art. In other words, the compressor cylinder 121 is designed to accommodate the compressor piston 122. That is, the compressor cylinder 121 is configured to compress a certain volume of air by the compressor piston and then deliver the compressed air to the combustor. To this end, the compressor cylinder includes a main cylinder volume 124. The main cylinder volume 124 is generally defined at the cylinder head of the compressor cylinder. In addition, as Figure 2 As shown in , the master cylinder volume is usually defined by the inner surface of the cylinder head in combination with the compressor piston 122, which also corresponds to a conventional cylinder and piston arrangement. Therefore, the master cylinder volume defines a first space for compressing the air.

[0088] In addition, if Figure 2 As shown and further Figures 3a to 3f As shown, the reciprocating compressor 120 includes a secondary adjustable volume 126. The secondary adjustable volume 126 is arranged to be in fluid communication with the main cylinder volume 124. As will be apparent from the following description of the reciprocating compressor 120, the secondary adjustable volume 126 is configured to adjust the total volume (internal space) of the reciprocating compressor 120. In this way, a variable geometric compression ratio can be provided during operation of the reciprocating compressor 120 and the ICE system 100.

[0089] For example, if Figure 2 As shown and more specifically as Figures 3a to 3f As shown in FIG. 1 , the secondary adjustable volume 126 is defined by a plurality of sub-compartments 127 and 128. Sub-compartment 127 provides a first dead volume of a first size. Similarly, sub-compartment 128 provides a second dead volume of a second size. Each of the two sub-compartments 127 and 128 defining fixed dead volumes of different sizes can be arranged to be in fluid communication with the primary cylinder volume. Typically, the secondary adjustable volume 126 is arranged to be fluidly connected to the primary cylinder volume by a valve (e.g., Figure 2 170) is in fluid communication with the master cylinder volume 124. In other words, each of the two sub-compartments 127 and 128 can be arranged to be in fluid communication with the master cylinder volume 124 via a valve 170, which will be further described below.

[0090] Thus, the secondary adjustable volume 126 is configured to provide geometric compression ratio control of the compressor cylinder 121 by adjusting the volume of the secondary adjustable volume 126 to a plurality of defined dead volumes. The adjacent secondary volumes here include a first sub-compartment 127 and a second sub-compartment 128. In addition, as Figure 2 As shown and further Figure 3a to Figure 3fAs shown in FIG. 1 , the first sub-compartment 127 and the second sub-compartment 128 have different sizes here. However, it should be noted that although the secondary adjustable volume here only includes the first sub-compartment 127 and the second sub-compartment 128 of different sizes, a secondary adjustable volume that can be adjusted to four different dead volumes is provided. Now referring to Figure 3c to Figure 3f An example of such a configuration of the secondary adjustable volume is described below.

[0091] As mentioned above, and for example Figure 3c As shown in , the reciprocating compressor 120 includes a valve 170. In this example embodiment, the valve is a rotatable valve assembly that is arranged to rotate, for example, clockwise relative to its central axis. Figure 3c to Figure 3f As shown, the valve can open and close the inlets of sub-compartments 127 and 128 respectively by rotating about its central axis. Figure 3a to Figure 3f In the example shown in , the geometric compression ratio control is provided by two fixed dead volumes of different sizes (defined by compartments 127 and 128). By controlling valve 170, the two sub-compartments 127 and 128 can be placed in fluid communication with the main cylinder volume 124 of the compressor 120.

[0092] exist Figure 3a to Figure 3f In the example embodiment shown, the dimensions of the first sub-compartment 127 are smaller than the dimensions of the second sub-compartment 128 .

[0093] Furthermore, as described above, valve 170 may regulate the passage of fluid medium between each of sub-compartments 127 and 128 and master cylinder volume 124 .

[0094] like Figure 3c As shown in , valve 170 is arranged in a position blocking the inlet of each of the two sub-compartments 127 and 128. In this configuration of the secondary adjustable volume 126, no additional dead volume is provided. Therefore, air compression in the compressor 120 occurs only in the primary cylinder volume 124.

[0095] like Figure 3d As shown in , valve 170 is arranged at a position blocking the entrance of the larger of these sub-compartments (i.e., sub-compartment 128) while providing fluid communication between the main cylinder volume 124 and another sub-compartment (which is the smaller of the sub-compartments, i.e., sub-compartment 127). Therefore, in this configuration of the secondary adjustable volume 126, a first dead volume of a first size is provided. To this end, air compression in the compressor 120 occurs in the sub-compartment 127 of the main cylinder volume 124 and the secondary adjustable volume 126.

[0096] like Figure 3eAs shown in , valve 170 is arranged at a position blocking the entrance of the smaller of these sub-compartments (i.e., sub-compartment 127) while providing fluid communication between the main cylinder volume 124 and another sub-compartment (which is the larger of the sub-compartments, i.e., sub-compartment 128). Therefore, in this configuration of the secondary adjustable volume 126, a second dead volume of a second size is provided. To this end, air compression in the compressor 120 occurs in the sub-compartment 128 of the main cylinder volume 124 and the secondary adjustable volume 126.

[0097] Finally, if Figure 3f As shown, valve 170 is arranged in a position providing access to two sub-compartments. In other words, valve 170 is controlled to place sub-compartments 127 and 128 in fluid communication with the main cylinder volume 124. Thus, in this configuration of the secondary adjustable volume 126, a third dead volume of a third size is provided. To this end, air compression in compressor 120 occurs in the main cylinder volume 124 and in the volume defined by sub-compartments 127 and 128 of the secondary adjustable volume 127.

[0098] Therefore, a plurality of different dead volume portions of different sizes may be provided. Figure 3c to Figure 3f The volumes described differ in size so that four different geometric compression ratios are available.

[0099] It should also be noted that the two sub-compartments 127 and 128 may have the same size. In such an example, a secondary adjustable volume having two different dead volumes is provided, one dead volume being defined by one of the sub-compartments and the other dead volume being defined by the combined size of the two sub-compartments.

[0100] It should be noted that multiple different sizes of dead volume parts can also be provided by other types of arrangements of sub-compartments in combination with other types of valves. In another example, the secondary adjustable volume can be provided by a conventional on / off valve, a slide valve, a reed valve or any other type of valve suitable for being arranged in a compressor environment. For example (although not shown), the secondary adjustable volume can also be provided by such a design: in this design, the slide valve is pressed against the port leading to the sub-compartment by the compression pressure in the compressor working chamber to seal. In such an example, the movement of the slide valve can occur at similar pressures between the main cylinder volume and the secondary adjustable volume.

[0101] In another example embodiment (although not shown), each of the two fixed dead volumes of different sizes are individually placed in fluid communication with the master cylinder volume via a first valve and a second valve, respectively.

[0102] Alternatively, if Figures 3a to 3fAs shown, the reciprocating compressor 120 also includes 172 and 174. That is, the reciprocating compressor 120 generally includes an inlet valve 172, which is used to control the inflow of air into the compressor. The inlet valve can be, for example, a conventional reed valve. In addition, the reciprocating compressor 120 includes an outlet valve 174, which is used to discharge the compressed air.

[0103] Furthermore, as described above, valve 170 can generally be controlled by control unit 180 .

[0104] In order to control air compression in relation to the operation of the ICE system, in particular the combustion reaction and vehicle operation, the geometric compression ratio control as described above is generally based on the engine characteristics of the ICE system. Therefore, although not strictly required, the volume of the secondary adjustable volume 126 is adjusted in response to the engine load of the ICE system.

[0105] The operation of the engine (i.e., the engine load) can be determined in several different ways. For example, the engine load of the ICE system is determined based on the actuation of the vehicle acceleration device (e.g., the accelerator pedal). The requested propulsion torque can be determined, for example, based on the position of the accelerator pedal manipulated by the driver. Typically, the ICE system includes a sensor that is arranged to collect data representing the engine load. The sensor can be arranged to communicate with a control unit of the ICE system or vehicle. The sensor (although not shown) can be arranged to detect changes in the engine load and / or determine the engine load of the ICE under a given operating state. Subsequently, the value of the engine load or an indication of the engine load change is transmitted to the control unit 180 for further processing. To this end, the control unit 180 is configured to determine the engine load of the ICE system based on the collected data, and further adjust the volume of the secondary adjustable volume in response to the determined engine load.

[0106] In another example embodiment, the ICE system includes a sensor device (although not shown) for detecting the position of the compressor piston 122 within the compressor cylinder 121. In addition, the volume of the secondary adjustable volume 126 is adjusted in response to the detected position of the compressor piston 122 within the compressor cylinder 121, so as to adjust the volume of the secondary adjustable volume 126 based on the operating point of the compressor 120.

[0107] Typically, the valve 170 is regulated (adjusted) by applying a force on the valve to rotate the valve to an open position. Similarly, the valve 170 rotates from one position to another when the pressure in the cylinder drops to a specific level that can be set by a control unit or a function of the valve.

[0108] Thus, engine load, and changes in engine load, can be monitored and determined in several different ways.

[0109] Optionally, the ICE system is operable so that during the compression stroke, the fluid communication between the primary cylinder volume 124 and the secondary adjustable volume 126 is always open. If the secondary adjustable volume is adjusted in response to the engine load, the ICE system is typically operable so that the fluid communication between the primary cylinder volume 124 and the secondary adjustable volume is always open during the compression stroke and until the engine load changes. However, it should be readily understood that in other cases, the fluid communication between the primary cylinder volume 124 and the secondary adjustable volume 126 may be controlled to be closed during the compression stroke.

[0110] Now turn to Figure 4 , the figure is Figure 1 100 is a perspective view of some additional components of an example embodiment of an ICE system 100. First, it should be noted that Figure 4 A complete illustration of a cylinder housing a corresponding piston has been omitted in order to simplify the understanding of the present disclosure and the piston construction.

[0111] Thus, although it should be noted that the ICE system may include multiple cylinders, the internal combustion engine system 100 herein may also include at least a piston burner assembly 110 having at least one combustion cylinder 111 accommodating a first combustion piston 112 and a second combustion cylinder 114 accommodating a second combustion piston 116. As described above, the internal combustion engine system 100 also includes a compressor 120 having a compressor cylinder 121 accommodating a compressor piston 122. In addition, as Figure 4 As shown, the ICE system 100 includes an expander 130 in the form of a two-stroke machine. The expander 130 includes an expander cylinder 131 accommodating an expander piston 132.

[0112] Turning again to the combustor assembly 110, it should be understood that the first combustion piston 112 and the second combustion piston 116 are individually disposed in the first combustion cylinder 111 and the second combustion cylinder 114 and are adapted to reciprocate therein. Accordingly, the compressor piston 122 and the expander piston 132 are disposed in the compressor cylinder 121 and the expander cylinder 131 and are adapted to reciprocate therein, respectively.

[0113] In addition, for example Figure 4 As shown in , the ICE system 100 includes a crankshaft 140. The crankshaft is rotatable about an axis of rotation, which generally corresponds to the longitudinal axis LA of the crankshaft. The rotatable crankshaft is generally arranged in an ICE system to be rotated by a power piston and also affect the linear motion of other pistons of the ICE system, as further described in more detail below.

[0114] As mentioned above, Figure 4 As shown in FIG. 1 , the ICE system 100 includes a compressor piston connecting rod 154 that connects the compressor piston 122 to the crankshaft 140. Figure 4 , the expander piston 132 is connected to the compressor piston 122 via a connecting element assembly 150. Alternatively, although not shown, the ICE system also includes an expander piston connecting rod that connects the expander piston 132 to the crankshaft 140. In this example, the expander piston 132 can still also be connected to the compressor piston 122 via a similar connecting element assembly.

[0115] Accordingly, if Figure 4 As shown in FIG. 1 , the first combustion piston connecting rod 163 connects the first combustion piston 112 to the crankshaft 140, and the second combustion piston connecting rod 164 connects the second combustion piston 114 to the crankshaft 140. Therefore, the above-mentioned reciprocating motion of the piston can be converted into the rotational motion of the crankshaft 140.

[0116] For example, Figure 4 As shown in FIG. 1 , the expander piston 132 is connected to the compressor piston 122 by a connecting element assembly 150 in the form of two connecting arms arranged in respective peripheral portions of the expander piston 132 and the compressor piston 122. Each connecting arm generally extends from the expander piston 132 to the compressor piston 122. Although in FIG. Figure 4 Two connecting arms are shown in the figure, but it should be understood that other numbers of connecting arms or only one connecting arm may also be used within the concept of the present disclosure. In addition, the connecting element assembly 150 may not be provided with a connecting arm, but may be provided instead as a connecting housing extending from the expander piston 132 to the compressor piston 122, for example, so that the expander piston 132 and the compressor piston 122 move in unison. The connecting element assembly 150 should rigidly connect the expander piston 132 to the compressor piston 122 so that the expander piston 132 and the compressor piston 122 move in unison. For example, the connecting element assembly 150 rigidly connects the expander piston 132 to the compressor piston 122 so that when the compressor piston 122 moves in a downward stroke (i.e., in order to compress the air in the compressor cylinder 121), the expander piston 132 moves in a stroke following the movement of the compressor piston 122. Accordingly, when the expander piston 132 moves in an upward stroke, the compressor piston 122 moves in a stroke following the movement of the expander piston 132.

[0117] like Figure 4 As shown in , the compressor cylinder 121 and the expander cylinder 131 are positioned on opposite sides of the crankshaft 140 and are in close proximity to the crankshaft. In other words, for example Figure 4As shown in , the main part of the crankshaft 140 is generally arranged between the expander piston 132 and the compressor piston 122, so that the main part of the crankshaft is arranged between the corresponding crankshaft-facing surfaces of the compressor piston and the expander piston. In other words, the compressor piston 122, the expander piston 132 and the main part of the crankshaft 140 are arranged along the geometric axis GA, and the main part of the crankshaft 140 is arranged between the compressor piston 122 and the expander piston 132 along the geometric axis GA. In this way, a so-called compressor-expander arrangement is provided that encloses the main part of the crankshaft 140. The internal positions of the components in the ICE system 100 can be described in different ways.

[0118] In at least a third way of describing the internal positions of components in the ICE system 100, the expander piston 132 has a circular or annular cross-section extending in a first geometric plane and the compressor piston 122 has a circular or annular cross-section extending in a second geometric plane, the first and second geometric planes being positioned in a parallel configuration on opposite sides of a longitudinal axis LA of the crankshaft 140.

[0119] For example Figure 4 As seen in FIG. 1 , the expander piston 132 is configured to reciprocate along the expander axis EA inside the expander cylinder 131. Accordingly, the compressor piston 122 is configured to reciprocate along the compressor axis CA inside the compressor cylinder 121. Accordingly, the first combustion piston 112 is configured to reciprocate along the combustion axis COA1 inside the first combustion cylinder 111, and the second combustion piston 116 is configured to reciprocate along the combustion axis COA2 inside the second combustion cylinder 114. For example Figure 4 As seen in FIG. 1 , the expander cylinder 131 and the compressor cylinder 121 are coaxially arranged, ie, the expander axis EA and the compressor axis CA are aligned.

[0120] Back to Figure 4 , showing that the first combustion cylinder 111 and the second combustion cylinder 114 can be described as protruding laterally from the crankshaft 140 compared to the expander cylinder 131. Therefore, the expander cylinder 131 and the first combustion cylinder 111 and the second combustion cylinder 114 are arranged in the ICE system 100 in such a way that the expander axis EA is at an angle between 40 and 90 degrees, preferably between 50 and 75 degrees, more preferably between 55 and 65 degrees, for example about 60 degrees, relative to each of the combustion axes COA1, COA2.

[0121] Now refer to Figure 4The function of the ICE system 100 is further clarified. The compressor cylinder 121 is configured to extract a certain volume of ambient air, compress the air and transmit the compressed air to the first combustion cylinder 111 and the second combustion cylinder 114. The first combustion cylinder 111 and the second combustion cylinder 114 are configured to be powered by combustion forces, such as by ignition of fuel (e.g., for gasoline or oil-driven engines) by spark plugs or heat from compression (e.g., for diesel-driven engines). The expander cylinder 131 is configured to receive exhaust gas from the first combustion piston 112 and the second combustion piston 116. The delivery of air, fuel and gas is performed by corresponding inlet valves, transfer ports and outlet valves well known to those skilled in the art, and the inlet valves, transfer ports and outlet valves fluidly interconnect the compressor cylinder 121, the first combustion cylinder 111 and the second combustion cylinder 114 and the expander cylinder 131.

[0122] In one example, the crankshaft is driven by at least one combustion piston via a corresponding combustion piston connecting rod and by an expander piston via a corresponding expander piston connecting rod, wherein the compressor piston is driven by the crankshaft via the expander piston.

[0123] However, a slightly opposite arrangement is also possible, which is also in Figure 4 ICE system. That is, the expander piston 132 is not directly connected to the crankshaft 140 via its own connecting rod, but is instead connected to the crankshaft 140 via the connecting element assembly 150, the compressor piston 122, and the compressor piston connecting rod 154. As a result, the rotational motion of the crankshaft 140 is converted into the reciprocating motion of the expander piston 132 via the compressor piston connecting rod 154. Therefore, the crankshaft 140 is driven by the first combustion piston 112 and the second combustion piston 116 through the corresponding combustion piston connecting rods, and is driven by the compressor piston through the compressor piston connecting rod 154, but the crankshaft 140 drives the expander piston 132 through the compressor piston 122 and the compressor piston connecting rod 154.

[0124] exist Figure 5 , a method 300 for controlling the geometric compression ratio of a reciprocating compressor 120 is depicted, as described above with reference to Figure 1 And further in Figure 3a to Figure 3f and Figure 4. The method is typically performed by the control unit 180 during operation of the ICE system 100. Optionally, as a first step, the method includes a step 305 of determining an engine load of the ICE system 100. The engine load can typically be determined as previously described herein. Subsequently, in step 310, the volume of the secondary adjustable volume 126 is adjusted to a first adjustment volume. That is, the volume of the secondary adjustable volume 126 is adjusted in response to the determined engine load. Thereafter, in step 320, the reciprocating compressor pressurizes the air to a first geometric compression ratio. Subsequently, as described above with respect to Figure 4 As described, the compressed air is delivered to the combustion cylinders.

[0125] It should be understood that the present disclosure is not limited to the embodiments described above and shown in the drawings; rather, those skilled in the art will recognize that many modifications and variations are possible within the scope of the appended claims.

Claims

1. An internal combustion engine system (100), comprising a reciprocating compressor (120), the reciprocating compressor being used to pressurize a fluid medium and having a compressor cylinder (121), the compressor cylinder being used to accommodate a compressor piston (122), the compressor cylinder having a primary cylinder volume (124) and a secondary adjustable volume (126), the secondary adjustable volume being in fluid communication with the primary cylinder volume to provide a variable geometric compression ratio, wherein: The secondary adjustable volume comprises a plurality of volume compartment portions of different sizes, and The total dead volume is provided by at least two volume compartment portions of different sizes, each of the two volume compartment portions of different sizes being respectively arranged to be in fluid communication with the master cylinder volume via at least one valve (170).

2. The internal combustion engine system according to claim 1, wherein: The secondary adjustable volume is configured to provide geometric compression ratio control of the compressor cylinders by adjusting the volume of the secondary adjustable volume to a plurality of defined volumes.

3. The internal combustion engine system according to claim 1 or 2, wherein: The secondary adjustable volume includes a plurality of fixed-sized volume compartment portions.

4. The internal combustion engine system according to claim 1, wherein: The at least one valve is a rotatable valve assembly arranged to open and close access to the at least two differently sized volume compartment portions, respectively, by rotation of the rotatable valve about its central axis.

5. The internal combustion engine system according to claim 1 or 2, wherein: The volume of the secondary adjustable volume is adjusted in response to an engine load of the internal combustion engine system.

6. The internal combustion engine system according to claim 5, wherein: The volume of the secondary adjustable volume is adjusted in response to a sensed position of the compressor piston in the compressor cylinder so as to adjust the volume of the secondary adjustable volume based on the engine load.

7. The internal combustion engine system according to claim 1 or 2, wherein: The internal combustion engine system is operable such that fluid communication between the primary cylinder volume and the secondary adjustable volume is always open during a compression stroke.

8. The internal combustion engine system according to claim 1 or 2, wherein: The internal combustion engine system comprises a control unit (180) for controlling the secondary adjustable volume (126).

9. The internal combustion engine system according to claim 1 or 2, wherein: The reciprocating compressor is operable by a crankshaft (140) of an internal combustion engine.

10. The internal combustion engine system according to claim 1 or 2, further comprising: at least one combustion cylinder housing a combustion piston, the combustion cylinder being configured to be powered by combustion forces; The compressor cylinder is configured to compress a volume of air and deliver the compressed air to the at least one combustion piston; an expander cylinder, the expander cylinder accommodating the expander piston (132), the expander cylinder being configured to receive exhaust gas from the at least one combustion piston.

11. A vehicle (1) comprising an internal combustion engine system (100) according to any one of claims 1-10.

12. A method for controlling a geometric compression ratio of a reciprocating compressor (120) of an internal combustion engine system (100), the reciprocating compressor (120) being configured to pressurize a fluid medium and having a compressor cylinder (121) for accommodating a compressor piston (122), the compressor cylinder having a primary cylinder volume (124) and a secondary adjustable volume (126), the secondary adjustable volume (126) being in fluid communication with the primary cylinder volume to provide a variable geometric compression ratio, wherein: The secondary adjustable volume comprises a plurality of volume compartment portions of different sizes, and wherein the total dead volume is provided by at least two volume compartment portions of different sizes, each of the two volume compartment portions of different sizes being respectively arranged to be in fluid communication with the primary cylinder volume via at least one valve (170), Wherein, the method comprises the following steps: - adjusting the volume of the secondary adjustable volume (126) to a first adjustment volume; and - pressurizing the fluid medium to a first geometric compression ratio by displacement of the compressor piston from bottom dead center to top dead center.

13. The method according to claim 12, further comprising the steps of: - determining an engine load of the internal combustion engine system; and - adjusting the volume of the secondary adjustable volume (126) in response to the determined engine load.

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