SE541125C2

SE541125C2 - Method of Estimating Pressure in a Cylinder of a Combustion Engine, Combustion Engine, and related devices

Info

Publication number: SE541125C2
Application number: SE1751031A
Authority: SE
Inventors: Erik Höckerdal; Joakim Sommansson
Original assignee: Scania Cv Ab
Priority date: 2017-08-29
Filing date: 2017-08-29
Publication date: 2019-04-16
Also published as: BR102018016989A2; SE1751031A1; DE102018006654A1; DE102018006654B4

Abstract

A method (100) of estimating a pressure in at least one cylinder (3.1 - 3.6) of an internal combustion engine (1), is disclosed, wherein the method (100) comprises the steps of selectively opening (110) at least one valve (9) into at least one cylinder (3.1 - 3.6) of the internal combustion engine (1), by providing a fluid pressure (p) in a fluid chamber (13), measuring (120) the fluid pressure (p) in the fluid chamber (13), and estimating (130) the pressure in the at least one cylinder (3.1 - 3.6) based on the measured fluid pressure (p) in the fluid chamber (13). The present disclosure further relates to a computer program, a computer-readable medium (200), a control arrangement (23), an internal combustion engine (1), and a vehicle (25) comprising an internal combustion engine (1).

Description

Method of Estimating Pressure in a Cylinder of a Combustion Engine, Combustion Engine, and related devices TECHNICAL FIELD The present disclosure relates to a method of estimating a pressure in at least one cylinder of an internal combustion engine. The present disclosure further relates to a computer program, and a computer program product for performing the method, a control arrangement configured to estimate a pressure in at least one cylinder of an internal combustion engine, an internal combustion engine, and a vehicle.

BACKGROUND Internal combustion engines, such as four-stroke internal combustion engines, comprise one or more cylinders and a piston arranged in each cylinder. The pistons are connected to a crankshaft of the engine and are arranged to reciprocate within the cylinders upon rotation of the crankshaft. The engine usually further comprises one or more inlet valves and one or more outlet valves as well as one or more fuel supply arrangements. The one or more inlet valves and outlet valves are controlled by a respective valve control arrangement usually comprising one or more camshafts rotatably connected to a crankshaft of the engine, via a belt, chain, gears, push rods, or similar. A four-stroke internal combustion engine completes four separate strokes while turning a crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The uppermost position of the piston in the cylinder is usually referred to as the top dead centre TDC, and the lowermost position of the piston in the cylinder is usually referred to as the bottom dead centre BDC.

The strokes are completed in the following order, inlet stroke, compression stroke, expansion stroke and exhaust stroke. During operation of a conventional four-stroke internal combustion engine, the inlet valve control arrangement controls inlet valves of a cylinder to an open state during the inlet stroke of a piston within the cylinder, to allow air, or a mixture of air and fuel, to enter the cylinder. During the compression stroke, all valves should be closed to allow compression of the air, or the mixture of the air and fuel, in the cylinder. If the engine is in a power producing state, fuel in the cylinder is ignited, usually towards the end of the compression stroke, for example by a spark plug or by compression heat in the cylinder. The combustion of fuel within the cylinder significantly increases pressure and temperature in the cylinder. The combustion of the fuel usually continues into a significant portion of the subsequent expansion stroke. The increased pressure and temperature in the cylinder obtained by the combustion is partially converted into mechanical work supplied to the crankshaft in the expansion stroke. Obviously, all valves should remain closed during the expansion stroke to allow the increased pressure and temperature to be converted into mechanical work. The expansion stroke is also usually referred to as the combustion stroke, because usually, the majority of the combustion takes place during the expansion stroke. In the subsequent exhaust stroke, the exhaust valve control arrangement controls exhaust valves of the cylinder to an open state to allow exhaust gases to be expelled out of the cylinder into an exhaust system.

During motoring, occurring for example when a driver of a vehicle releases an accelerator pedal, the engine will continue to operate in the above described strokes, with the exception that, normally, no fuel is supplied to the engine during motoring, and consequently, no combustion will take place during the end of the compression stroke or during the expansion stroke. In this condition, the engine will provide some braking torque due to internal friction and due to the pumping of air from the inlet to the exhaust, in the respective inlet stroke and exhaust stroke. As a piston travels upward during the compression stroke, the gases that are trapped in the cylinder are compressed. The compressed gases oppose the upward motion of the piston. However, almost all of the energy stored in the compressed gases is returned to the crankshaft on the subsequent expansion stroke. Thereby, during normal motoring, the compression stroke together with the subsequent expansion stroke, will not contribute to a significant braking torque of the engine.

A compression release brake arrangement is an engine braking mechanism used in some engines. When activated, it opens exhaust valves in the cylinders after the compression stroke, releasing the compressed air trapped in the cylinders to the exhaust system.

Thereby, the energy stored in the compressed gases during the compression stroke will not be returned to the crankshaft on the subsequent expansion stroke, which increases the braking torque of the engine.

In some arrangements, the exhaust valves may be deactivated, so that they remain closed during the exhaust stroke. Usually, this is achieved using a so called lost motion arrangement, which when actuated is arranged to not transfer motion caused by an exhaust cam lobe to the exhaust valve. The air in the cylinders will thereby be compressed also during the exhaust stroke. By using a valve control arrangement opening exhaust valves near the end of the exhaust stroke, the compressed air trapped in the cylinders is released to the exhaust system. Such arrangement almost doubles the braking torque since compression and release events are performed in the compression stroke as well as in the exhaust stroke.

In a compression ignition engine, such as a diesel engine, it is the heat from the compressed gases that ignites the fuel. In a spark-ignition engine, such as an Otto engine, it is a spark plug that ignites the fuel. The compression in the cylinders are an important factor for the operation and the efficiency of the engine. The pressure in the cylinders obtained during compression indicates the compression in the cylinders. The compression in cylinders of an engine may degrade over time because components of the engine are subjected to wear and tear, such as the cylinder, the piston, piston rings, valves, valve seats, etc. Further, in an engine comprising more than one cylinder, which most vehicle engines do, one or more of the cylinders may be worn in an unforeseeable way. In such a situation, the vehicle can be driven many miles before the worn cylinder gets noticed, for example during a service procedure. Still, even during a service procedure, the worn cylinder may not be noticed, which may cause further damages to the engine.

The pressure in the cylinders of an engine, and thus also the compression of the cylinders, can be measured using a pressure gauge arranged in each cylinder. However, this is an expensive solution for obtaining the pressure in the cylinders, especially for an engine comprising several cylinders. In addition, due to the rough environment within a cylinder of a combustion engine, i.e. due to the considerable heat, pressure and vibrations in the cylinder, such pressure gauges will likely be damaged during the life time of the engine, which will add further costs for the replacement.

Thus, the use of pressure gauges arranged in each cylinder is an expensive and sensitive solution for obtaining the pressure in the cylinders. As a reason thereof, the most common way to determine the pressure in the cylinders is to perform a manual compression measurement in a workshop using a manometer. Such a procedure is burdensome and costly and must be performed on each cylinder individually. Further, such a procedure lacks the ability to provide an instantaneous measurement of the pressure in the cylinders, for example during running of the engine. Still further, in most cases, such a procedure does not form part of a service schedule and will therefore not be performed if the engine seems to otherwise run properly. Still further, many vehicles run a lot of miles between the service intervals. Accordingly, the compression of one or more cylinders may degrade significantly before being detected.

SUMMARY It is an object of the present invention to overcome, or at least alleviate, at least some of the above-mentioned problems and drawbacks.

According to a first aspect of the invention, the object is achieved by a method of estimating a pressure in at least one cylinder of an internal combustion engine, wherein the internal combustion engine comprises: - the at least one cylinder, - a piston arranged in each cylinder, - a crankshaft, - at least one valve arranged in each cylinder, wherein the at least one valve is arranged to control flow of gas into, and/or out of, the cylinder, - a valve control arrangement comprising a fluid chamber, and - a sensor configured to measure fluid pressure in the fluid chamber, wherein the method comprises the steps of: - selectively opening the at least one valve into the at least one cylinder, by providing a fluid pressure in the fluid chamber, - measuring the fluid pressure in the fluid chamber, and - estimating the pressure in the at least one cylinder based on the measured fluid pressure in the fluid chamber.

Since the method comprises the step of estimating the pressure in the at least one cylinder based on the measured fluid pressure in the fluid chamber, a method is provided which estimates the pressure in the at least one cylinder in an efficient, reliable and cost-effective manner. Further, a method is provided capable of estimating the compression of at least one cylinder in an efficient, reliable and cost-effective manner, since the pressure in the cylinder is indicative of the compression in the cylinder. Still further, conditions are provided for obtaining an instantaneous estimation of the pressure in the at least one cylinder, and compression of the at least one cylinder, for example during motoring of the internal combustion engine in an efficient, reliable and cost-effective manner. Still further, since an instantaneous estimation of the compression in the at least one cylinder can be obtained in an efficient, reliable and cost-effective manner, conditions are also provided for detecting if one or more component of the engine that is related to the compression of the at least one cylinder has been subjected to wear that reduces the compression, such as the piston, piston rings of the piston, the at least one valve, valve seats of the at least one valve, valve lash of the at least one valve, etc. As a result, such wear of components can be detected at an early stage which reduces the risk of excessive wear of the components, as well as further components of the internal combustion engine, and thereby potentially reduces the cost for service and repair of the internal combustion engine. Further, since wear of components can be detected at an early stage, the method provides conditions for performing a conditionbased maintenance of an internal combustion engine.

Accordingly, a method is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

Optionally, the piston is arranged to reciprocate in the at least one cylinder between a bottom dead centre and a top dead centre, wherein the method comprises the step of: - opening the at least one valve into the at least one cylinder, when the piston is in a region of the top dead centre.

Thereby, the pressure in the cylinder, and thus also the compression in the cylinder, can be estimated in a more accurate manner, since the pressure in the cylinder is higher when the piston is in a region of the top dead centre, than when the piston is in a region of the bottom dead centre.

Optionally, the valve control arrangement comprises a valve actuator, and wherein the fluid chamber is arranged between the valve actuator and the at least one valve.

Thereby, the estimation of the pressure in the at least one cylinder can be made in an efficient and reliable manner, because the measured fluid pressure in the fluid chamber provides a clear and reliable indication of the pressure in the at least one cylinder.

Optionally, the method is performed during engine braking of the internal combustion engine, during motoring of the internal combustion engine, or during cranking of the internal combustion engine. As a result, a method is provided which estimates the pressure in the at least one cylinder in a still more efficient and reliable manner. This because no combustion occurs during engine braking, during cranking, as well as during motoring. As a further result thereof, the compression of the at least one cylinder can be estimated in a still more efficient and reliable manner since the pressure in the at least one cylinder, during engine braking, during motoring, as well as during cranking, provides a clear indication of the compression of the at least one cylinder. Further, an internal combustion engine of a vehicle performs engine braking, motoring, as well as cranking frequently. Therefore, the method can be performed frequently which further provides conditions for detecting wear of components at an early stage, thus further reducing the risk of excessive wear of components, and thus potentially further reducing the cost for service and repair of the internal combustion engine.

Optionally, the internal combustion engine comprises a compression release brake arrangement comprising the valve control arrangement, wherein the compression release brake arrangement is configured to selectively perform compression release braking of the internal combustion engine, and wherein the method is performed during the compression release braking. As a result, a method is provided which estimates the pressure in the at least one cylinder in a still more efficient and reliable manner. This because no combustion occurs during the compression release braking. As a further result thereof, the compression of the at least one cylinder can be estimated in a still more efficient and reliable manner since the pressure in the at least one cylinder, during compression release braking, provides a clear indication of the compression of the at least one cylinder. Further, an internal combustion engine of a vehicle in normal traffic will perform compression release braking frequently. Therefore, the method can be performed frequently which further provides conditions for detecting wear of components at an early stage, thus further reducing the risk of excessive wear of components, and thus potentially further reducing the cost for service and repair of the internal combustion engine.

Optionally, the internal combustion engine comprises at least two cylinders and a crank angle sensor, wherein the method comprises the steps of: - monitoring a series of consecutive pressure increase events of the measured fluid pressure, and - identifying a correlation between one or more consecutive pressure increase events and one of the at least two cylinders by comparing the consecutive pressure increase events and the crank angle of the crankshaft.

Thereby, a method is provided capable of identifying the correlation between the estimated pressures and the cylinders which gives the possibility to identify a cylinder having a deviant cylinder pressure in an engine comprising more than one cylinder. Further, conditions are provided for of estimating the pressure in two or more cylinders of an engine using only one sensor. Thereby, a method is provided capable of estimating the pressure in two or more cylinders of an internal combustion engine, in an efficient, reliable and cost-effective manner.

According to a second aspect of the invention, the object is achieved by a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to embodiments described herein. Since the computer program comprises instructions which, when the program is executed by a computer, cause the computer to carry out the method according to embodiments described herein, a computer program is provided which provides conditions for overcoming, or at least alleviating, at least some of the above-mentioned drawbacks.

According to a third aspect of the invention, the object is achieved by a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to embodiments described herein. Since the computerreadable medium comprises instructions which, when the program is executed by a computer, cause the computer to carry out the method according to embodiments described herein, a computer-readable medium is provided which provides conditions for overcoming, or at least alleviating, at least some of the above-mentioned drawbacks.

According to a fourth aspect of the invention, the object is achieved by a control arrangement configured to estimate a pressure in at least one cylinder of an internal combustion engine, wherein the internal combustion engine comprises: - the at least one cylinder, - a piston arranged in each cylinder, - a crankshaft, - at least one valve arranged in each cylinder, wherein the at least one valve is arranged to control flow of gas into, and/or out of, the cylinder, - a valve control arrangement comprising a fluid chamber, and - a sensor configured to measure fluid pressure in the fluid chamber, wherein the control arrangement is configured to: - selectively open the at least one valve into the at least one cylinder, by providing a fluid pressure in the fluid chamber, - measure the fluid pressure in the fluid chamber, and - estimate the pressure in the at least one cylinder based on the measured fluid pressure in the fluid chamber.

Since the control arrangement is configured to estimate the pressure in the at least one cylinder based on the measured fluid pressure in the fluid chamber, a control arrangement is provided which estimates the pressure in the at least one cylinder in an efficient, reliable and cost-effective manner. Further, a control arrangement is provided capable of estimating the compression of at least one cylinder in an efficient, reliable and cost-effective manner, since the pressure in the cylinder is indicative of the compression in the cylinder. Still further, a control arrangement is provided capable of obtaining an instantaneous estimation of the pressure in the at least one cylinder, and compression of the at least one cylinder, for example during motoring of the internal combustion engine in an efficient, reliable and costeffective manner. Still further, since an instantaneous estimation of the compression in the at least one cylinder can be obtained in an efficient, reliable and cost-effective manner, conditions are also provided for detecting if one or more component of the engine that is related to the compression of the at least one cylinder has been subjected to wear that reduces the compression, such as the piston, piston rings of the piston, the at least one valve, valve seats of the at least one valve, valve lash of the at least one valve, etc. As a result, such wear of components can be detected at an early stage which reduces the risk of excessive wear of the components, as well as further components of the internal combustion engine, and thereby potentially reduces the cost for service and repair of the internal combustion engine. Further, since the wear of components can be detected at an early stage, the control arrangement provides conditions for performing a condition-based maintenance of an internal combustion engine comprising the control arrangement.

Accordingly, a control arrangement is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

According to a fifth aspect of the invention, the object is achieved by an internal combustion engine comprising: - at least one cylinder, - a piston arranged in each cylinder, - a crankshaft, - at least one valve arranged in each cylinder, wherein the at least one valve is arranged to control flow of gas into, and/or out of, the cylinder, - a valve control arrangement comprising a fluid chamber, - a sensor configured to measure fluid pressure in the fluid chamber, and - a control arrangement configured to: - selectively open the at least one valve into the at least one cylinder, by providing a fluid pressure in the fluid chamber, - measure the fluid pressure in the fluid chamber, and - estimate the pressure in the at least one cylinder based on the measured fluid pressure in the fluid chamber.

Since the control arrangement of the internal combustion engine is configured to estimate the pressure in the at least one cylinder based on the measured fluid pressure in the fluid chamber, an internal combustion engine is provided capable of estimating the pressure in the at least one cylinder in an efficient, reliable and cost-effective manner. Further, an internal combustion engine is provided capable of estimating the compression of at least one cylinder in an efficient, reliable and cost-effective manner, since the pressure in the cylinder is indicative of the compression in the cylinder. Still further, internal combustion engine is provided capable of obtaining an instantaneous estimation of the pressure in the at least one cylinder, and compression of the at least one cylinder, for example during motoring of the internal combustion engine in an efficient, reliable and cost-effective manner. Still further, since an instantaneous estimation of the compression in the at least one cylinder can be obtained in an efficient, reliable and cost-effective manner, conditions are also provided for detecting if one or more component of the internal combustion engine that is related to the compression of the at least one cylinder has been subjected to wear that reduces the compression, such as the piston, piston rings of the piston, the at least one valve, valve seats of the at least one valve, valve lash of the at least one valve, etc. As a result, such wear of components can be detected at an early stage which reduces the risk of excessive wear of the components, as well as further components of the internal combustion engine, and thereby potentially reduces the cost for service and repair of the internal combustion engine. Further, since the wear of components can be detected at an early stage, conditions are provided for performing a condition-based maintenance of the internal combustion engine.

Accordingly, an internal combustion engine is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the abovementioned object is achieved.

Optionally, the piston is arranged to reciprocate in the at least one cylinder between a bottom dead centre and a top dead centre, wherein the control arrangement is configured to: - open the at least one valve into the at least one cylinder, when the piston is in a region of the top dead centre.

Optionally, the valve control arrangement comprises a valve actuator, and wherein the fluid chamber is arranged between the valve actuator and the at least one valve. Thereby, the estimation of the pressure in the at least one cylinder can be made in an efficient and reliable manner, because the measured fluid pressure in the fluid chamber provides a clear and reliable indication of the pressure in the at least one cylinder.

Optionally, the internal combustion engine comprises a compression release brake arrangement comprising the valve control arrangement. Thus, according to these embodiments, the control arrangement of the internal combustion engine may selectively open the at least one valve into the at least one cylinder, measure the fluid pressure in the fluid chamber, and estimate the pressure in the at least one cylinder based on the measured fluid pressure in the fluid chamber, during compression release braking. Thereby, the pressure in the at least one cylinder can be estimated in a still more efficient and reliable manner. This because no combustion occurs during the compression release braking. As a further result thereof, the compression of the at least one cylinder can be estimated in a still more efficient and reliable manner since the pressure in the at least one cylinder, during compression release braking, provides a clear indication of the compression of the at least one cylinder. Further, an internal combustion engine of a vehicle in normal traffic will perform compression release braking frequently. Therefore, the estimation of the pressure in the at least one cylinder can be performed frequently which further provides conditions for detecting wear of components at an early stage, thus further reducing the risk of excessive wear of components, and thus potentially further reducing the cost for service and repair of the internal combustion engine.

Optionally, wherein the internal combustion engine comprises at least two cylinders and a crank angle sensor, wherein the control arrangement is configured to: - monitor a series of consecutive pressure increase events of the measured fluid pressure, and - identify a correlation between one or more consecutive pressure increase events and one of the at least two cylinders by comparing the consecutive pressure increase events and the crank angle of the crankshaft.

Thereby, an internal combustion engine is provided capable of identifying the correlation between the estimated pressures and the cylinders which gives the possibility to identify a cylinder having a deviant cylinder pressure. Further, conditions are provided for of estimating the pressure in two or more cylinders of an internal combustion engine using only one sensor. Thereby, an internal combustion engine is provided capable of estimating the pressure in two or more cylinders, in an efficient, reliable and cost-effective manner.

According to a sixth aspect of the invention, the object is achieved by a vehicle comprising wheels and an internal combustion engine according to some embodiments, wherein the internal combustion engine is configured to provide motive power to the vehicle via one or more of the wheels of the vehicle.

Since the vehicle comprises an internal combustion engine overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks, a vehicle is provided overcoming, or at least alleviating, at least some of the above-mentioned problems and drawbacks. As a result, the above-mentioned object is achieved.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS Various aspects 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 illustrates schematically a cross sectional view of an internal combustion engine, according to some embodiments, Fig. 2 illustrates schematically a side view of the internal combustion engine illustrated in Fig. 1, Fig. 3 illustrates a graph showing a series of consecutive pressure increase events of a measured fluid pressure in a fluid chambers of the internal combustion engine, illustrated in Fig. 1 and Fig. 2, Fig. 4 illustrates a vehicle comprising wheels and the internal combustion engine illustrated in Fig. 1 and Fig. 2, Fig. 5 illustrates a method of estimating a pressure in at least one cylinder of an internal combustion engine, and Fig. 6 illustrates computer-readable medium.

DETAILED DESCRIPTION Aspects of the present 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 illustrates schematically a cross sectional view of an internal combustion engine 1, according to some embodiments. Herein, the internal combustion engine 1 is in some cases referred to as “the engine 1” for the reason of brevity and/or clarity. The engine 1 comprises at least one cylinder 3.1 and a piston 5 arranged in each cylinder 3.1. The piston 5 is connected to a crankshaft 7, via a connecting rod 6. The piston 5 moves forwards and backwards in the cylinder 3.1 upon rotation of the crankshaft 7, between a top dead centre TDC and a bottom dead centre BDC. The engine 1 comprises an inlet system 8, which in the illustrated example embodiments is illustrated as an inlet duct. The inlet system 8 may comprise further components such as an air filter, a throttle, a fuel injector, an air flow sensor, etc.

The engine 1 further comprises at least one inlet valve 10 arranged in each cylinder 3.1, which at least one inlet valve 10 is connected with the inlet system 8. The inlet valve 10 is arranged to control flow of gas into the cylinder 3.1. The engine 1 further comprises an inlet valve control arrangement 12.1 configured to control each inlet valve 10 on the basis of a rotational position of the crankshaft 7. The engine 1 further comprises at least one exhaust valve 9 arranged in each cylinder 3.1, which at least one exhaust valve 9 is connected with an exhaust outlet 14 of the engine 1. The exhaust valve 9 is arranged to control flow of gas out of the cylinder 3.1. The engine 1 further comprises an exhaust valve control arrangement 12.2 configured to control each exhaust valve 9 on the basis of the rotational position of the crankshaft 7. In Fig. 1, the at least one inlet valve 10 and the at least one exhaust valve 9 are illustrated in a respective closed position. In the closed position, each valve 9, 10 abuts against a respective valve seat to close fluid connection between the cylinder 3.1 and the respective inlet system 8 and the exhaust outlet 14.

The inlet valve control arrangement 12.1 is arranged to control the at least one inlet valve 10 between the closed position and an open position by displacing the at least one inlet valve 10 in a direction into the cylinder 3.1. A fluid connection is thereby opened between the inlet system 8 and the cylinder 3.1. Likewise, the exhaust valve control arrangement 12.2 is arranged to control the at least one exhaust valve 9 between the closed position and an open position by displacing the at least one exhaust valve 9 in a direction into the cylinder 3.1. Thereby, a fluid connection is opened between the cylinder 3.1 and the exhaust outlet 14. Upon displacement of a valve 9, 10 from the closed position to the open position, the valve 9, 10 is lifted from its valve seat. According to the illustrated embodiments, the at least one exhaust valve 9, as well as the at least one inlet valve 10, comprises a poppet valve, which also may be referred to as a mushroom valve.

The engine 1 further comprises a fuel injector 16 arranged to directly inject fuel into the cylinder 3.1. The engine 1 in the illustrated embodiments is a compression ignition engine. According to further embodiments, the engine may be an Otto engine with a spark-ignition device, wherein the Otto engine may be designed to run on gas, petrol, alcohol or similar volatile fuels or combinations thereof. The fuel may be directly injected into the cylinder 3.1 using a fuel injector, or may be added to incoming air prior to entering the cylinder 3.1, for example by a fuel injector arranged at an inlet duct of the engine 1.

The exhaust valve control arrangement 12.2 and the inlet valve control arrangement 12.1 may each comprise one or more camshafts rotatably connected to the crankshaft 7, wherein the camshafts comprises cam lobes 20.1, 20.2 arranged to displace valves 9, 10 to an open position by pressing on valve stems of the valves 9, 10 upon rotation of the camshaft 7. The cam lobes 20.1, 20.2 may press directly onto the valve stems of the valves 9, 10, or may press onto the valve stems of the valves 9, 10 via further arrangements such as push rods, rocker arms, hydraulic arrangements, or the like. The exhaust valve control arrangement 12.2, and/or the inlet valve control arrangement 12.1, may according to further embodiments comprise electric, pneumatic or hydraulic actuators arranged to control the valves 9, 10 on the basis of the rotational position of the crankshaft 7. The rotational position of the crankshaft 7 may be obtained using a crank angle sensor 22.

The engine 1 further comprises a valve control arrangement 11. The valve control arrangement 11 may be arranged at the exhaust valve control arrangement 12.2 and may utilize and/or share components thereof, as is the case according to the illustrated embodiments. The valve control arrangement 11 comprises a fluid component 18 comprising a fluid chamber 13. According to the illustrated embodiments, the fluid component 18 is a hydraulic component and the fluid chamber 13 is a hydraulic chamber. The valve control arrangement 11 comprises a valve actuator 19. According to the illustrated embodiments, the valve actuator 19 comprises a cam lobe arranged at a camshaft 17. According to further embodiments, the valve actuator may comprise a rocker arm that may be connected to a camshaft for example via one or more push rods, or the like. The fluid component 18 and the fluid chamber 13 is arranged between the valve actuator 19 and the at least one valve 9. The valve actuator 19 is arranged to abut against a portion 18.1 of the fluid component 18. The fluid component 18 is arranged to transfer movement from the valve actuator 19 to the valve 9 when a fluid pressure is provided in the fluid chamber 13. The fluid component 18 is arranged to not transfer movement from the valve actuator 19 to the valve 9 when no fluid pressure is provided in the fluid chamber 13. According to the illustrated embodiments, the fluid pressure in the fluid chamber 13 is provided by closing a first control valve 24 so that the movement of the valve actuator 19 can build up a fluid pressure in the fluid chamber 13 to thereby transfer movement from the valve actuator 19 to the valve 9, as will be further explained below.

The internal combustion engine 1 comprises a compression release brake arrangement 21. The compression release brake arrangement 21 is configured to selectively perform compression release braking of the internal combustion engine 1. According to the illustrated embodiments, the valve control arrangement 11 forms part of the compression release brake arrangement 21. The valve control arrangement 11 is configured to selectively open the exhaust valve 9 into the at least one cylinder 3.1 near the end of the compression stroke of the engine 1. Thereby, the energy stored in the compressed gases during the compression stroke will not be returned to the crankshaft 7 on the subsequent expansion stroke, which increases the braking torque of the engine 1. The valve control arrangement 11 is configured to selectively open the exhaust valve 9 into the at least one cylinder 3.1 by providing a fluid pressure in the fluid chamber 13.

According to the illustrated embodiments, the valve control arrangement 11 comprises the first control valve 24 and a second control valve 26. The second control valve 26 is connected to a pressurized fluid circuit 28 and to the first control valve 24. According to the illustrated embodiments, the fluid circuit 28 is an oil circuit. The oil circuit may form part of an engine oil circuit of the engine 1.

The engine 1 comprises a control arrangement 23 configured to control at least the second control valve 26. During a power producing state of the engine 1, the control arrangement 23 controls the second control valve 26 to a closed state. When the second control valve 26 is in the closed state, no fluid pressure is applied to the first control valve 24. When no fluid pressure is applied to the first control valve 24, the first control valve 24 is in an open state. When the first control valve 24 is in the open state, fluid, e.g. oil, can flow into, and out of, the fluid chamber 13 via the first control valve 24 upon rotation of the camshaft 17. Thereby, the movement of the valve actuator 19 will not be transferred to the exhaust valve 9. As a result, the valve actuator 19 will not force the exhaust valve 9 to open when the second control valve 26 is in the closed state. However, according to the illustrated embodiments, the cam lobe 20.2 of the exhaust valve control arrangement 12.2 will force the exhaust valve 9 to open when the second control valve 26 is in the closed state. This because the cam lobe 20.2 of the exhaust valve control arrangement 12.2 is provided with a greater height than the valve actuator 19 and thereby will provide a greater stroke length than the valve actuator 19, and because the fluid component 18 is configured to transfer movement of the cam lobe 20.2 to the exhaust valve 9 when subjected to the stroke length of the cam lobe 20.2. As a result, the engine 1 can operate in a power producing state when the second control valve 26 is in the closed state.

To initiate compression release braking, the compression release brake arrangement 21 controls the second control valve 26 to an open state. In the open state, the second control valve 26 applies a fluid pressure to the first control valve 24. When a fluid pressure is applied to the first control valve 24, the first control valve 24 assumes an active state. In the active state, the first control valve 24 allows fluid to flow into the fluid chamber 13 and hinders fluid to flow out of the fluid chamber 13. As a result, the fluid chamber will be filled with fluid upon rotation of the camshaft 17. When the fluid chamber 13 is filled with fluid and when the valve actuator 19 of the camshaft 17 pushes onto the portion 18.1 of the fluid component 18, the force of the valve actuator 19 is transferred to the exhaust valve 9, via the fluid component 18, which forces the exhaust valve 9 to the open position.

The internal combustion engine 1 comprises a sensor 15 configured to measure fluid pressure in the fluid chamber 13. The exhaust valve 9 comprises a certain surface area facing into the cylinder, and the fluid chamber 13 is provided with a certain cross-sectional area. Thus, the measured fluid pressure in the fluid chamber 13 provides a clear and reliable indication of the pressure in the cylinder 3.1 at the time of the opening of the exhaust valve 9. The control arrangement 23 is connected to the sensor 15 and is configured to estimate the pressure in the at least one cylinder 3.1 based on the measured fluid pressure in the fluid chamber 13. In addition to the measured fluid pressure in the fluid chamber 13, the estimation of the pressure in the at least one cylinder 3.1 may be based on the surface area of the exhaust valve 9 facing the cylinder 3.1, the cross-sectional area of the fluid chamber 13, rotational speed of the internal combustion engine 1, friction losses, the pressure in the inlet system 8, boost pressure of a charging device, etc.

The control arrangement 23 is configured to open the at least one valve 9 into the at least one cylinder 3.1, when the piston 5 is in a region of the top dead centre, such as when the piston is within the interval of 20 crank angle degrees before top dead centre to 20 crank angle degrees after top dead centre. The pressure within a cylinder of an engine is the highest when the piston is at the top dead centre. By opening the at least one valve 9 into the at least one cylinder 3.1, when the piston 5 is in the region of the top dead centre, the braking force of the engine 1 is increased. Further, the estimation of the pressure in the cylinder 3.1 can be performed in a reliable manner due to the high pressure. According to the illustrated embodiments, the control arrangement 23 is configured to open the at least one valve 9 into the at least one cylinder, measuring the fluid pressure in the fluid chamber 13, and estimating the pressure in the at least one cylinder 3.1 based on the measured fluid pressure in the fluid chamber 13 during engine braking. According to further embodiments, the control arrangement 23 may, as an alternative, or in addition, be configured to open the at least one valve 9 into the at least one cylinder 3.1, measuring the fluid pressure in the fluid chamber 13, and estimating the pressure in the at least one cylinder 3.1 based on the measured fluid pressure in the fluid chamber 13 during motoring and/or cranking of the engine 1.

According to some embodiments, the control arrangement 23 may be configured to open the at least one valve 9 into the at least one cylinder 3.1, when the piston 5 is at a distance from the bottom dead centre, by performing a phase shift of the exhaust valve control arrangement 12.2. Thereby, the cam lobe 20.2 of the exhaust valve control arrangement 12.2 will force the exhaust valve 9 to open when the piston 5 is at a distance from the bottom dead centre and the pressure in the at least one cylinder 3.1 can be estimated based on the measured fluid pressure in the fluid chamber 13. According to such embodiments, the engine 1 may comprise a phase shifting device instead of, or in addition to, the compression release brake arrangement 21.

Fig. 2 illustrates schematically a side view of the internal combustion engine 1 illustrated in Fig. 1. The internal combustion engine 1 comprises six cylinders 3.1 - 3.6 arranged in line. The engine illustrated in Fig. 2 may thus be referred to as an inline-six cylinder engine. The internal combustion engine 1 may comprise another number of cylinders than six, which may be arranged in another configuration than in inline, as will be further explained below. The cylinder 3.1 illustrated in Fig. 1 is the first cylinder 3.1 of the six cylinders 3.1 - 3.6 illustrated in Fig. 2. The remaining cylinders 3.2 - 3.6 of the six cylinders 3.1 - 3.6 each comprises a piston, at least one valve arranged in the cylinder 3.2 - 3.6, wherein the at least one valve is arranged to control flow of gas into, and/or out of, the cylinder 3.2 - 3.6, and a valve control arrangement provided with a fluid component comprising a fluid chamber. The second control valve 24 of the compression release brake arrangement 21 is fluidically connected to each fluid chamber of each cylinder 3.1 - 3.6 via a fluid connection. The sensor 15 illustrated in Fig. 1 is configured to measure fluid pressure p in the fluid connection. Thereby, the fluid pressure in each fluid chamber can be sensed using one sensor 15. In embodiments where the engine comprises cylinders arranged in more than one row, such as in a V configuration engine, the engine may comprise one sensor 15 per row of cylinders. Accordingly, a V configuration engine may comprise two sensors 15.

Fig. 3 illustrates a graph showing a series of consecutive pressure increase events p1 - p6 of the measured fluid pressure p in the fluid chambers 13 of the internal combustion engine 1 illustrated in Fig. 1 and Fig. 2. The vertical axis of the graph shows the fluid pressure p and the horizontal axis shows the rotational position a of the crankshaft 7 of the engine 1.

According to the illustrated embodiments, the control arrangement 23 is configured to monitor a series of consecutive pressure increase events p1 - p6 of the measured fluid pressure p, and identify a correlation between one or more consecutive pressure increase events p1 - p6 and one of the at least two cylinders 3.1 - 3.6 by comparing the consecutive pressure increase events p1 - p6 and the crank angle a of the crankshaft 7. The comparison between the consecutive pressure increase events p1 - p6 and the crank angle a of the crankshaft 7 may encompass a comparison between the position of the consecutive pressure increase events p1 - p6 and the crank angle a of the crankshaft 7. Thereby, a cylinder having a deviant cylinder pressure can be identified in an efficient, reliable and costeffective manner. Further, conditions are provided for of estimating the pressure in two or more cylinders of an internal combustion engine using only one sensor.

Further, as illustrated in Fig. 3, the control arrangement may compare each pressure increase event p1 - p6 and a first threshold value t1 and a second threshold value t2. In such embodiments, the control arrangement 23 may determine a cylinder pressure of a cylinder to be too low if the peak of a pressure increase event p1 - p6 is below the first threshold value t1. In Fig. 3, the pressure increase event p5 is below the first threshold value. According to the illustrated embodiments, the pressure increase event p5 belongs to the cylinder 3.5, which, as explained above, may be identified by comparing the consecutive pressure increase events p1 - p6 and the crank angle a of the crankshaft 7. The control arrangement 23 may determine a cylinder pressure of a cylinder to be too high if the peak of a pressure increase event p1 - p6 is above the second threshold value t2. A too high cylinder pressure may be caused by a worn camshaft which may cause one or more valves to open too late. The control arrangement 23 may output an alert in a driver environment of a vehicle hosting the internal combustion engine 1 if the estimated cylinder pressure is above the second threshold value t2 and/or below the first threshold value t1. The first and/or the second threshold value t1, t2 may be determined on the basis of the rotational speed of the internal combustion engine 1, friction losses, the pressure in the inlet system 8, boost pressure of a charging device, etc.

According to further embodiments, the control arrangement 23 may determine a cylinder pressure of a cylinder to be too low or too high by comparing the pressure increase events p1 - p6 and identifying if one or more of the pressure increase events p1 - p6 deviates significantly from the other pressure increase events p1 - p6. Thereby, a cylinder having a too high or a too low cylinder pressure can be detected in a simple, effective and reliable manner.

Further, according to some embodiments, the control arrangement 23 may be configured to compare the phase and/or duration of monitored pressure increase events p1 - p6 with stored and/or predetermined values for phase and/or duration of pressure increase events. Thereby, a control arrangement 23 can be provided with an improved ability to detect if components of the engine 1 have been subjected to wear and tear that affects the compression in the cylinders of the engine 1.

Fig. 4 illustrates a vehicle 25 comprising wheels 27 and the internal combustion engine 1 illustrated in Fig. 1 and Fig. 2. The internal combustion engine 1 is configured to provide motive power to the vehicle 25 via one or more of the wheels 27 of the vehicle 25.

The vehicle 25 illustrated in Fig. 4 is a truck. However, the internal combustion engine 1 may be comprised in another type of manned or unmanned vehicle for land or water based propulsion such as a lorry, a bus, a construction vehicle, a tractor, a car, a boat, a ship, or the like. Further, the internal combustion engine 1 as referred to herein may be a stationary internal combustion engine, for example an internal combustion engine of an engine driven generator Fig. 5 illustrates a method 100 of estimating a pressure in at least one cylinder of an internal combustion engine. The internal combustion engine may be an internal combustion engine 1 according to the embodiments illustrated in Fig. 1 and Fig. 2. Further, some features and advantages are explained with reference to Fig. 3. Therefore, below, reference is made to Fig. 1, Fig. 2, as well as to Fig. 3. The method 100 is a method of estimating a pressure in at least one cylinder 3.1 - 3.6 of an internal combustion engine 1, wherein the internal combustion engine 1 comprises: - the at least one cylinder 3.1 - 3.6, - a piston 5 arranged in each cylinder 3.1 - 3.6, - a crankshaft 7, - at least one valve 9 arranged in each cylinder 3.1 - 3.6, wherein the at least one valve 9 is arranged to control flow of gas into, and/or out of, the cylinder 3.1 -3.6, - a valve control arrangement 11 comprising a fluid chamber 13, and - a sensor 15 configured to measure fluid pressure p in the fluid chamber 13, wherein the method 100 comprises the steps of: - selectively opening 110 the at least one valve 9 into the at least one cylinder 3.1 - 3.6, by providing a fluid pressure p in the fluid chamber 13, - measuring 120 the fluid pressure p in the fluid chamber 13, and - estimating 130 the pressure in the at least one cylinder 3.1 - 3.6 based on the measured fluid pressure p in the fluid chamber 13.

According to some embodiments, the piston 5 is arranged to reciprocate in the at least one cylinder 3.1 - 3.6 between a bottom dead centre and a top dead centre, wherein the method 100 comprises the step of: - opening 111 the at least one valve 9 into the at least one cylinder 3.1 - 3.6, when the piston 5 is in a region of the top dead centre.

According to some embodiments, the valve control arrangement 11 comprises a valve actuator 19, and wherein the fluid chamber 13 is arranged between the valve actuator 19 and the at least one valve 9.

According to some embodiments, the method 100 is performed during engine braking of the internal combustion engine 1, during motoring of the internal combustion engine 1, or during cranking of the internal combustion engine 1.

According to some embodiments, the internal combustion engine 1 comprises a compression release brake arrangement 21 comprising the valve control arrangement 11, wherein the compression release brake arrangement 21 is configured to selectively perform compression release braking of the internal combustion engine 1, and wherein the method 100 is performed during the compression release braking.

According to some embodiments, the internal combustion engine 1 comprises at least two cylinders 3.1 - 3.6 and a crank angle sensor 22, wherein the method 100 comprises the steps of: - monitoring 140 a series of consecutive pressure increase events p1 - p6 of the measured fluid pressure p, and - identifying 150 a correlation between one or more consecutive pressure increase events p1 - p6 and one of the at least two cylinders 3.1 - 3.6 by comparing the consecutive pressure increase events p1 - p6 and the crank angle a of the crankshaft 7.

It will be appreciated that the various embodiments described for the method 100 are all combinable with the control arrangement 23 as described herein. That is, the control arrangement 23 may be configured to perform any one of the method steps 110, 120, 130, 140, 150, and 111 of the method 100. Further, the method 100 as described herein may be performed during engine braking, during motoring, and/or during cranking of the internal combustion engine 1.

Fig. 6 illustrates computer-readable medium 200 comprising instructions which, when executed by a computer, cause the computer to carry out the method 100 according to some embodiments.

According to some embodiments, the computer-readable medium 200 comprises a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method 100 according to some embodiments.

One skilled in the art will appreciate that the method of estimating a pressure in at least one cylinder of an internal combustion engine may be implemented by programmed instructions. These programmed instructions are typically constituted by a computer program, which, when it is executed in the control arrangement 23, ensures that the control arrangement 23 carries out the desired control, such as the method steps 110, 120, 130, 140, 150, and 111 described herein. The computer program is usually part of a computer program product 200 which comprises a suitable digital storage medium on which the computer program is stored.

The control arrangement 23 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 arrangement 23 may further comprise a memory unit, wherein the calculation unit may be connected to the memory unit, which may provide the calculation unit with, for example, stored program code and/or stored data which the calculation unit may need to enable it to do calculations. The calculation unit may also be adapted to store 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. According to some embodiments, the memory unit may comprise integrated circuits comprising silicon-based transistors. The memory unit may comprise e.g. a memory card, a flash memory, a USB memory, a hard disc, or another similar volatile or non-volatile storage unit for storing data such as e.g. ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), etc. in different embodiments.

The control arrangement 23 is connected to components of the internal combustion engine 1 for receiving and/or sending input and output signals. These input and output signals may comprise waveforms, pulses or other attributes which the input signal receiving devices can detect as information and which can be converted to signals processable by the control arrangement 23. These signals may then be supplied to the calculation unit. One or more output signal sending devices may be arranged to convert calculation results from the calculation unit to output signals for conveying to other parts of the vehicle's control system and/or the component or components for which the signals are intended. Each of the connections to the respective components of the internal combustion engine 1 for receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (controller area network) bus, a MOST (media orientated systems transport) bus or some other bus configuration, or a wireless connection.

In the embodiments illustrated, the internal combustion engine 1 comprises a control arrangement 23 but might alternatively be implemented wholly or partly in two or more control arrangements or two or more control units.

Control systems in modern vehicles generally comprise a communication bus system consisting of one or more communication buses for connecting a number of electronic control units (ECUs), or controllers, to various components on board the vehicle. Such a control system may comprise a large number of control units and taking care of a specific function may be shared between two or more of them. Vehicles of the type here concerned are therefore often provided with significantly more control arrangements than depicted in Fig. 1, as one skilled in the art will surely appreciate.

The computer program product 200 may be provided for instance in the form of a data carrier carrying computer program code for performing at least some of the method steps 110, 120, 130, 140, 150, and 111 according to some embodiments when being loaded into one or more calculation units of the control arrangement 23. The data carrier may be, e.g. a CD ROM disc, as is illustrated in Fig. 6, or a ROM (read-only memory), a PROM (programable read-only memory), an EPROM (erasable PROM), a flash memory, an EEPROM (electrically erasable PROM), a hard disc, a memory stick, an optical storage device, a magnetic storage device or any other appropriate medium such as a disk or tape that may hold machine readable data in a non-transitory manner. The computer program product may furthermore be provided as computer program code on a server and may be downloaded to the control arrangement 23 remotely, e.g., over an Internet or an intranet connection, or via other wired or wireless communication systems.

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 present invention, as defined by the appended claims. As explained above, the fluid chamber and the fluid component may, according to some embodiments comprise a hydraulic chamber and a hydraulic component. Thus, throughout this disclosure, the word “fluid” may be replaced with the word “hydraulic”, or with the word “liquid”. For example, the hydraulic chamber and a hydraulic component may form part of a cylinder deactivation arrangement using hydraulic fluid, or a lost motion arrangement using hydraulic fluid.

The cylinders 3.1 - 3.6 each form a combustion chamber. Thus, throughout this disclosure, the word “cylinder” may be replaced with the word “combustion chamber”.

As used herein, the term "comprising" or "comprises" is open-ended, and includes one or more stated features, elements, steps, components or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions or groups thereof.

Claims

1. A method (100) of estimating a pressure in at least one cylinder (3.1 - 3.6) of an internal combustion engine (1), wherein the internal combustion engine (1) comprises: - the at least one cylinder (3.1 - 3.6), - a piston (5) arranged in each cylinder (3.1 - 3.6), - a crankshaft (7), - at least one valve (9) arranged in each cylinder (3.1 - 3.6), wherein the at least one valve (9) is arranged to control flow of gas into, and/or out of, the cylinder (3.1 - 3.6), - a valve control arrangement (11) comprising a fluid chamber (13), and - a sensor (15) configured to measure fluid pressure (p) in the fluid chamber (13), wherein the method (100) comprises the steps of: - selectively opening (110) the at least one valve (9) into the at least one cylinder (3.1 -3.6), by providing a fluid pressure (p) in the fluid chamber (13), - measuring (120) the fluid pressure (p) in the fluid chamber (13), and - estimating (130) the pressure in the at least one cylinder (3.1 - 3.6) based on the measured fluid pressure (p) in the fluid chamber (13).

2. The method (100) according to claim 1, wherein the piston (5) is arranged to reciprocate in the at least one cylinder (3.1 - 3.6) between a bottom dead centre and a top dead centre, wherein the method (100) comprises the step of: - opening (111) the at least one valve (9) into the at least one cylinder (3.1 - 3.6), when the piston (5) is in a region of the top dead centre.

3. The method (100) according to claim 1 or 2, wherein the valve control arrangement (11) comprises a valve actuator (19), and wherein the fluid chamber (13) is arranged between the valve actuator (19) and the at least one valve (9).

4. The method (100) according to any one of the claims 1 - 3, wherein the method (100) is performed during engine braking of the internal combustion engine (1), during motoring of the internal combustion engine (1), or during cranking of the internal combustion engine (1).

5. The method (100) according to any one of the preceding claims, wherein the internal combustion engine (1) comprises a compression release brake arrangement (21) comprising the valve control arrangement (11), wherein the compression release brake arrangement (21) is configured to selectively perform compression release braking of the internal combustion engine (1), and wherein the method (100) is performed during the compression release braking.

6. The method (100) according to any one of the preceding claims, wherein the internal combustion engine (1) comprises at least two cylinders (3.1 - 3.6) and a crank angle sensor (22), wherein the method (100) comprises the steps of: - monitoring (140) a series of consecutive pressure increase events (p1 - p6) of the measured fluid pressure (p), and - identifying (150) a correlation between one or more consecutive pressure increase events (p1 - p6) and one of the at least two cylinders (3.1 - 3.6) by comparing the consecutive pressure increase events (p1 - p6) and the crank angle (a) of the crankshaft (7).

7. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method (100) according to any one of the claims 1 - 6.

8. A computer-readable medium (200) comprising instructions which, when executed by a computer, cause the computer to carry out the method (100) according to any one of the claims 1 - 6.

9. A control arrangement (23) configured to estimate a pressure in at least one cylinder (3.1 - 3.6) of an internal combustion engine (1), wherein the internal combustion engine (1) comprises: - the at least one cylinder (3.1 - 3.6), - a piston (5) arranged in each cylinder (3.1 - 3.6), - a crankshaft (7), - at least one valve (9) arranged in each cylinder (3.1 - 3.6), wherein the at least one valve (9) is arranged to control flow of gas into, and/or out of, the cylinder (3.1 - 3.6), - a valve control arrangement (11) comprising a fluid chamber (13), and - a sensor (15) configured to measure fluid pressure (p) in the fluid chamber (13), wherein the control arrangement (23) is configured to: - selectively open the at least one valve (9) into the at least one cylinder (3.1 - 3.6), by providing a fluid pressure (p) in the fluid chamber (13), - measure the fluid pressure (p) in the fluid chamber (13), and - estimate the pressure in the at least one cylinder (3.1 - 3.6) based on the measured fluid pressure (p) in the fluid chamber (13).

10. An internal combustion engine (1) comprising: - at least one cylinder (3.1 - 3.6), - a piston (5) arranged in each cylinder (3.1 - 3.6), - a crankshaft (7), - at least one valve (9) arranged in each cylinder (3.1 - 3.6), wherein the at least one valve (9) is arranged to control flow of gas into, and/or out of, the cylinder (3.1 - 3.6), - a valve control arrangement (11) comprising a fluid chamber (13), - a sensor (15) configured to measure fluid pressure (p) in the fluid chamber (13), and - a control arrangement (23) configured to: - selectively open the at least one valve (9) into the at least one cylinder (3.1 - 3.6), by providing a fluid pressure (p) in the fluid chamber (13), - measure the fluid pressure (p) in the fluid chamber (13), and - estimate the pressure in the at least one cylinder (3.1 - 3.6) based on the measured fluid pressure (p) in the fluid chamber (13).

11. The internal combustion engine (1) according to claim 10, wherein the piston (5) is arranged to reciprocate in the at least one cylinder (3.1 - 3.6) between a bottom dead centre and a top dead centre, wherein the control arrangement (23) is configured to: - open the at least one valve (9) into the at least one cylinder (3.1 - 3.6), when the piston (5) is in a region of the top dead centre.

12. The internal combustion engine (1) according to claim 10 or 11, wherein the valve control arrangement (11) comprises a valve actuator (19), and wherein the fluid chamber (13) is arranged between the valve actuator (19) and the at least one valve (9).

13. The internal combustion engine (1) according to any one of the claims 10 - 12, wherein the internal combustion engine (1) comprises a compression release brake arrangement (21) comprising the valve control arrangement (11).

14. The internal combustion engine (1) according to any one of the claims 10 - 13, wherein the internal combustion engine (1) comprises at least two cylinders (3.1 - 3.6) and a crank angle sensor (22), wherein the control arrangement (23) is configured to: - monitor a series of consecutive pressure increase events (p1 - p6) of the measured fluid pressure (p), and - identify a correlation between one or more consecutive pressure increase events (p1 - p6) and one of the at least two cylinders (3.1 - 3.6) by comparing the consecutive pressure increase events (p1 - p6) and the crank angle (a) of the crankshaft (7).

15. A vehicle (25) comprising wheels (27) and an internal combustion engine (1) according to any one of the claims 10 - 14, wherein the internal combustion engine (1) is configured to provide motive power to the vehicle (25) via one or more of the wheels (27) of the vehicle (25).