INTERNAL COMBUSTION ENGINE AND METHOD OF CLEANING OF CRANKCASE GAS

Abstract

 Herein an internal combustion engine, ICE, 30 is disclosed. The ICE 30 comprises a fluid pump, and a centrifugal separator 20 for cleaning of crankcase gas. The fluid pump 34 is driven by the ICE 30 for providing a pressurised fluid. The centrifugal separator 20 comprises a centrifugal rotor and a drive arrangement, the drive arrangement being configured to utilise the pressurised fluid for driving the centrifugal rotor. The fluid pump 34 is configured to vary a pressure of the pressurised fluid independently of a rotational speed of the ICE 30. A control unit 40 of the ICE 30 is configured to control the fluid pump 34 to regulate the pressure of the pressurised fluid towards a target pressure based on at least one operational parameter of the ICE 30. The target pressure corresponds to a target rotational speed of the centrifugal rotor.

Description

TECHNICAL FIELD

[0001] The invention relates to an internal combustion engine comprising a crankcase, a fluid pump, and a centrifugal separator for cleaning of crankcase gas. The invention further relates to a method of operating a centrifugal separator for cleaning of crankcase gas from an internal combustion engine.

BACKGROUND

[0002] Crankcase gas from an internal combustion engine is ventilated from a crankcase of the internal combustion engine. Crankcase gas may be disposed of in an environmentally friendly manner instead of being ventilated in untreated form to the atmosphere. For certain types of combustion engines, legislation requires crankcase gas to be disposed of in an environmentally friendly manner.

[0003] Crankcase gas may comprise inter alia blow-by gases, oil, other liquid hydrocarbons, soot, and other solid combustion residues. In order to dispose of crankcase gas, suitably, the gas is separated as a gaseous phase from a liquid phase, which contains the oil, soot, and other residues. The gaseous phase may be led to an air intake of the combustion engine or vented to the atmosphere, and the liquid phase may be led back to an oil sump of the combustion engine, optionally, via an oil filter for removing soot and other solid residues from the oil and the other liquid hydrocarbons.

[0004] A centrifugal separator may be utilised for cleaning of crankcase gas. In the centrifugal separator, the crankcase gas is separated into the gaseous phase and the liquid phase. Separation discs of the centrifugal separator, in the form of frustoconical discs, are arranged in a disc stack with short distance interspaces between the separation discs. The crankcase gas is lead into the rotating disc stack and heavy constituents of the crankcase gas, such as oil and soot, are forced against inner surfaces of the separation discs and form droplets of the liquid phase as they travel along the separation discs towards an outer periphery of the disc stack. The droplets are thrown onto an inner wall of a housing of the centrifugal separator. The liquid phase is lead out of the centrifugal separator via a liquid outlet. The gaseous phase is lead out of the centrifugal separator via a gas outlet.

[0005] US 9322307 discloses a device for cleaning a gas which is contaminated with particles, and includes a centrifugal separator with a centrifugal rotor for separating the particles from the gas and a drive arrangement for rotating the centrifugal rotor about a rotational axis. The drive arrangement includes an impulse turbine drivingly connected to the centrifugal rotor and a nozzle for directing a pressurized fluid towards the impulse turbine. In order to rotate the centrifugal rotor, a jet of pressurized fluid from the nozzle is directed against the impulse turbine.

[0006] SE 200502503 discloses a method of cleaning crankcase gas from an engine. A centrifugal separator is utilised for the cleaning. The engine comprises a hydraulic system comprising an oil pump and a valve arrangement for distributing oil for driving the centrifugal separator and for other purposes. The engine also includes an exhaust gas brake for applying additional braking power via an exhaust gas brake throttle. When the exhaust gas brake is activated, the valve arrangement is configured to prioritise and increase oil supply to the centrifugal separator in order to increase the rotational speed and the cleaning capacity of the centrifugal separator.

[0007] US 7875098 discloses a centrifugal separator comprising a stationary casing defining an inner space, a spindle and a rotating member, which is attached to the spindle and arranged to rotate around an axis of rotation with a rotary speed. The rotating member comprises a number of separating discs which are provided in the inner space. A drive member comprising a blade wheel driven by a liquid jet, drives the spindle and the rotating member with said rotary speed. A sensor device senses the rotation of the rotating member in relation to the casing. In such a way, the rotary speed of the rotating member may be determined. The determined rotary speed may be used for controlling the number of revolutions of the drive member.

SUMMARY

[0008] In particular onboard a vehicle, energy consumption of a centrifugal separator for cleaning of crankcase gas is of concern, not only in a centrifugal separator driven with an electric motor, but also in a centrifugal separator comprising a fluid driven turbine. The pressure of the fluid for driving the centrifugal separator has to be provided by the engine, the crankcase gas of which is to be cleaned.

[0009] It is an object of the invention to provide for reduced energy consumption in an internal combustion engine comprising a fluid driven centrifugal separator for cleaning of crankcase gas.

[0010] According to an aspect of the invention, the object is achieved by an internal combustion engine comprising a crankcase, a fluid pump, and a centrifugal separator for cleaning of crankcase gas. The fluid pump is directly or indirectly driven by the internal combustion engine for providing a pressurised fluid. The centrifugal separator comprises a centrifugal rotor and a drive arrangement, the drive arrangement being configured to utilise the pressurised fluid for driving the centrifugal rotor. The fluid pump is configured to vary a pressure of the pressurised fluid independently of a rotational speed of the internal combustion engine, and the internal combustion engine comprises a control unit configured to control the fluid pump to regulate the pressure of the pressurised fluid towards a target pressure based on at least one operational parameter of the internal combustion engine, the target pressure corresponding to a target rotational speed of the centrifugal rotor.

[0011] Since the fluid pump is configured to vary a pressure of the pressurised fluid independently of a rotational speed of the internal combustion engine, and the internal combustion engine comprises a control unit configured to control the fluid pump to regulate the pressure of the pressurised fluid towards a target pressure based on at least one operational parameter of the internal combustion engine, wherein the target pressure corresponds to a target rotational speed of the centrifugal rotor, provisions are made for the pressure of the pressurised fluid to be regulated in order to meet a cleaning demand of the crankcase gas currently produced based on the operational parameter of the internal combustion engine, ICE. Thus, only a necessary amount of energy from the ICE has to be utilised for driving the centrifugal separator and the cleaning of crankcase gas. As a result, the object is achieved.

[0012] More specifically, the cleaning capacity and efficiency of the centrifugal separator depends on the rotational speed of the centrifugal rotor. Thus, at a low flow of crankcase gas a lower rotational speed of the centrifugal rotor is sufficient for cleaning the generated crankcase gas, in comparison with when the ICE produces a high flow of crankcase gas and a higher rotational speed of the centrifugal rotor is required for cleaning the generated crankcase gas. The at least one operational parameter of the ICE provides a direct or indirect indication of the amount of crankcase gas generated in the crankcase of the ICE.

[0013] In the centrifugal separator, the crankcase gas is separated into a gaseous phase and a liquid phase. The centrifugal separator may comprise separation discs, e.g. in the form of frustoconical discs, which are arranged in a disc stack with short distance interspaces between the separation discs. The crankcase gas is lead into the rotating centrifugal rotor. The separated liquid phase is lead out of the centrifugal separator via a liquid outlet, e.g. to an oil trough of the ICE. The gaseous phase is lead out of the centrifugal separator via a gas outlet, e.g. to a fresh gas inlet of the ICE. The ICE comprises at least one piston arranged to reciprocate in a cylinder bore of the ICE. A connecting rod connects the piston with a crankshaft arranged in the crankcase.

[0014] According to embodiments, the at least one operational parameter may comprise a current engine power developed by the internal combustion engine. In this manner, the rotational speed of the centrifugal rotor may be controlled based on the currently developed engine power. The amount of crankcase gas to be cleaned varies dependent on the currently developed engine power. Thus, the currently developed engine power may form a suitable parameter for controlling the rotational speed of the centrifugal rotor. The current engine power developed by the ICE may be either a directly measured engine power, a calculated engine power, or given by a different parameter directly related to the current engine power developed by the ICE.

[0015] According to embodiments, the internal combustion engine may comprise a pressure sensor configured for measuring a current pressure of the pressurised fluid and being connected to the control unit. In this manner, the control unit may control the fluid pump to regulate the pressure of the pressurised fluid towards the target pressure based on the measured current pressure of the pressurised fluid from the pressure sensor.

[0016] According to embodiments, the centrifugal separator may comprise a rotational speed sensor connected to the control unit, and wherein the control unit is configured to determine a current rotational speed of the centrifugal rotor via the rotational speed sensor. In this manner, the control unit may control the fluid pump to regulate the pressure of the pressurised fluid towards the target pressure based on the measured current rotational speed of the centrifugal rotor.

[0017] It is a further object of the invention to provide a method for reduced energy consumption of a fluid driven centrifugal separator for cleaning of crankcase gas of an internal combustion engine.

[0018] According to an aspect of the invention, the object is achieved by a method of operating a centrifugal separator for cleaning of crankcase gas from an internal combustion engine, the internal combustion engine comprising a crankcase, a fluid pump, and the centrifugal separator. The fluid pump is directly or indirectly driven by the internal combustion engine for providing a pressurised fluid. The centrifugal separator comprises a centrifugal rotor and a drive arrangement for driving the centrifugal rotor. The fluid pump is configured to vary a pressure of the pressurised fluid independently of a rotational speed of the internal combustion engine. The method comprises steps of:

• directing the pressurised fluid towards an impeller of the drive arrangement, and
• regulating the pressure of the pressurised fluid towards a target pressure based on at least one operational parameter of the internal combustion engine, the target pressure corresponding to a target rotational speed of the centrifugal rotor.

[0019] Since the method comprises steps of:

• directing the pressurised fluid towards an impeller of the drive arrangement, and
• regulating the pressure of the pressurised fluid towards a target pressure based on at least one operational parameter of the internal combustion engine, the target pressure corresponding to a target rotational speed of the centrifugal rotor, the method provides for pressure regulation of the pressurised fluid in order to meet a cleaning demand of the crankcase gas currently produced based on the operational parameter of the internal combustion engine. Thus, only a necessary amount of energy from the internal combustion engine has to be utilised for driving the centrifugal separator and the cleaning of crankcase gas. As a result, the object is achieved.

[0020] Further features of, and advantages with, the invention will become apparent when studying the appended claims and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Various aspects and/or embodiments of the invention, including its particular features and advantages, will be readily understood from the example embodiments discussed in the following detailed description and the accompanying drawings, in which:

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

Fig. 2 schematically illustrates a cross section through a centrifugal separator according to embodiments,

Fig. 3 shows a diagram providing a schematic example of the amount of crankcase gas produced by an internal combustion engine,

Fig. 4 schematically illustrates embodiments of a control system of an internal combustion engine,

Figs. 5a and 5b schematically illustrate fluid pumps according to embodiments, and

Fig. 6 illustrates embodiments of a method of operating a centrifugal separator for cleaning of crankcase gas from an internal combustion engine.

DETAILED DESCRIPTION

[0022] Aspects and/or embodiments of the invention will now be described more fully. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

[0023] Fig. 1 schematically illustrates an internal combustion engine, ICE, 30 according to embodiments. The ICE 30 comprises a crankcase 32, a fluid pump 34, and a centrifugal separator 20 for cleaning of crankcase gas.

[0024] The ICE 30 may be a compression ignition or spark ignition four-stroke or two-stroke ICE. In a known manner, the ICE 30 comprises at least one piston arranged in a cylinder bore of the ICE 30. A connecting rod connects the piston with a crankshaft 31 inside the crankcase 32. As fuel combusts in a combustion chamber formed above the piston in the cylinder bore, the piston reciprocates in the cylinder bore and drives the crankshaft 31.

[0025] Some of the combustion gases produced in the combustion chamber flow past the piston into the crankcase 32. This is called blow-by gas. For the piston to be able to reciprocate freely, the crankcase 32 has to be ventilated. Thus, crankcase gas flows from the crankcase 32 to the centrifugal separator 20. In addition to blow-by gas, the crankcase gas may comprise, oil, other liquid hydrocarbons, soot, and other solid combustion residues.

[0026] A conduit 36 fluidly connects an interior of the crankcase 32 with the centrifugal separator 20. In the centrifugal separator 20, the crankcase gas is separated into a gaseous phase and a liquid phase. The separated liquid phase is lead out of the centrifugal separator 20 via a liquid outlet 16, back to the crankcase 32. The gaseous phase is lead out of the centrifugal separator 20 via a gas outlet 15, to a fresh gas inlet of the ICE 30.

[0027] The fluid pump 34 is directly or indirectly driven by the ICE 30 for providing a pressurised fluid, see further below. The pressurised fluid discussed in these example embodiments is lubricating oil of the ICE 30, but may alternatively be any other suitable fluid, such as e.g. a coolant of the ICE 30.

[0028] Fig. 2 schematically illustrates a cross section through a centrifugal separator 20 according to embodiments. The centrifugal separator 20 is an example centrifugal separator for cleaning of crankcase gases to be utilised in an ICE as discussed in connection with Fig. 1.

[0029] The centrifugal separator 20 comprises a stationary housing 1 and a centrifugal rotor 4 rotatably arranged inside the stationary housing 1. The stationary housing 1 defines an inner space 2'. The stationary housing 1 has an inner wall surface 1a, which faces the inner space 2' and an outer wall surface 1b which faces outwardly towards an ambient environment of the centrifugal separator 20. The stationary housing 1 comprises an inlet 13 for crankcase gas, a gas outlet 15 for the gaseous phase, and a liquid outlet 16 for the liquid phase, as discussed above. The inner space 2' has an upper end 11 and a lower end 12. The inlet 13 for crankcase gases extends through the housing 1 at the upper end 11 into the inner space 2'. In these embodiments, the gas outlet 15 and the liquid outlet 16 are provided at a proximity of the lower end 12.

[0030] The centrifugal rotor 4 comprises a stack of frustoconical separation discs 5. The centrifugal rotor 4 comprises a spindle 3. The spindle 3 is journaled in two bearings, an upper spindle bearing 8 and a lower spindle bearing 9. The centrifugal separator 20 comprises a drive arrangement 10 for driving the centrifugal rotor 4. The drive arrangement 10 in these embodiments is provided in a separate space 2" below the inner space 2'. The drive arrangement 10 comprises an impeller 10a which is driven by a pressurised fluid. The centrifugal rotor 4 is brought to rotate about a rotational axis x in the inner space 2' by the pressurised fluid being directed against the impeller 10a. Accordingly, the drive arrangement 10 is configured to utilise the pressurised fluid for driving the centrifugal rotor 4.

[0031] Depending on the size of the relevant ICE, the crankcase gas of which is to be cleaned, a full stack of separation discs 5 of a centrifugal separator may comprise for instance 50 - 200 separation discs. Mentioned purely as an example, a separation disc 5 may have a diameter of approximately 100 mm, a thickness of approximately 0,35 mm (not including any distance elements), and interspaces between adjacent separation discs 5 may be approximately 0,3 mm.

[0032] The crankcase gas to be cleaned is fed into the centrifugal separator 20 through the inlet 13. The centrifugal separator 20 is configured to lead crankcase gas from the inlet 13 into a central portion of the centrifugal rotor 4. From the central portion, the crankcase gas is led into interspaces between the separation discs 5. When the crankcase gas arrives in the inner space 2' and is brought to rotate by the centrifugal rotor 4, the heavy constituents will abut against the separation discs 5 and by means of centrifugal force will be thrown from an outer periphery of the centrifugal rotor 4 against the inner wall surface 1a of the stationary housing 1. The gaseous phase, which in such a way has been cleaned from liquid and solid constituents, is then conveyed downwardly in the inner space 2' and out through the gas outlet 15. The liquid phase flows on the inner wall surface 1a down into an annular collection groove 17 and out through the liquid outlet 16.

[0033] In the illustrated embodiments, the pressurised fluid is a lubricating oil of the ICE which is being utilised in the drive arrangement 10. After use in the drive arrangement 10, the oil flows back to the ICE via the liquid outlet 16. In case of a different fluid than lubricating oil of the ICE being utilised as the pressurised fluid, the liquid phase has to be kept separate from the pressurised fluid. The liquid phase is returned to the ICE via the liquid outlet, and the pressurised fluid is lead out of the centrifugal separator 20 via a separate outlet.

[0034] Referring to Figs. 1 and 2, the fluid pump 34 is configured to vary a pressure of the pressurised fluid independently of a rotational speed of the ICE 30. That is, the fluid pump 34 may be controlled to provide a high pressure or a low pressure of the pressurised fluid at a low RPM of the ICE 30. Similarly, the fluid pump 34 may be controlled to provide a high pressure or a low pressure of the pressurised fluid at a high RPM of the ICE 30. Since the fluid pump 34 is configured to vary a pressure of the pressurised fluid independently of a rotational speed of the ICE 30, and since the centrifugal separator 20 is driven by the pressurised fluid from the fluid pump 34, the rotational speed of the centrifugal rotor 4 may be controlled independently of the rotational speed of the ICE 30. Thus, since the amount of crankcase gas from the crankcase 32 of the ICE 30 not necessarily correlates with the rotational speed of the ICE 30, energy may be saved as the fluid pump 34 may be controlled to provide a rotational speed of the centrifugal rotor of the centrifugal separator 20 sufficient for cleaning of a currently produced amount of crankcase gas, but controlled to not rotate at a higher rotational speed.

[0035] The ICE 30 comprises a control unit 40 configured to control the fluid pump 34 to regulate the pressure of the pressurised fluid towards a target pressure. Control of the fluid pump 34 by the control unit 40 is based on at least one operational parameter of the ICE 30. The target pressure corresponds to a target rotational speed of the centrifugal rotor 4. That is, at the target pressure of the pressurised fluid, the target rotational speed of the centrifugal rotor 4 is reached. At a lower pressure than the target pressure, the rotational speed of the centrifugal rotor 4 is lower than the target rotational speed. At a higher pressure than the target pressure, the rotational speed of the centrifugal rotor 4 is higher than the target rotational speed. The required target pressure varies during operation of the ICE 30 in correspondence with the currently produced amount of crankcase gas. The at least one operational parameter of the ICE 30 reflects the currently produced amount of crankcase gas and thus, the current cleaning need of the centrifugal separator 20.

[0036] By controlling the fluid pump 34 based on the at least one operational parameter of the ICE 30 towards the target pressure, it may be ensured that the centrifugal rotor 4 is rotating at a rotational speed sufficient for cleaning currently produced crankcase gas in the ICE 30, and that the centrifugal rotor 4 is not rotate at an unnecessarily high rotational speed, thus, saving energy in the ICE 30.

[0037] Naturally, other components or functions of the ICE 30 may require a certain minimum fluid pressure. Accordingly, the target pressure may have a minimum pressure level, which may be maintained even if the amount of crankcase gas currently produced in the ICE 30 would require a lower fluid pressure for sufficient cleaning of the currently produced amount of crankcase gas. However, in many operating situations of the ICE 30 it is the centrifugal separator 20 that requires the highest fluid pressure, and thus, determines the target pressure.

[0038] The target pressure may be assessed directly or indirectly. In the former case, the target pressure may be calculated, or collected from a lookup table, based on the at least one operational parameter. In the latter case, the target pressure may be expressed by a different parameter than pressure, again, based on the at least one operational parameter, such as e.g., by the target rotational speed of the centrifugal separator 20, by a target angular velocity of the fluid pump 34, or by a target mechanical setting of the fluid pump 34. Accordingly, the control unit 40 controls the fluid pump 34 to regulate the pressure of the pressurised fluid, but the control unit 40 need not necessarily perform the control based on actual pressure values.

[0039] The at least one operational parameter may comprise a current engine power developed by the ICE 30. Thus, the rotational speed of the centrifugal rotor 4 may be controlled based on the currently developed engine power. The amount of crankcase gas produced in the ICE 30 dependents inter alia on the currently developed engine power. For each type of ICE the amount of crankcase gas produced is different. Generally, however, the amount of crankcase gas from an ICE increases with increased developed engine power. Thus, for instance a mathematical formula or a lookup table may provide a relevant target pressure for the currently developed engine power.

[0040] For instance, a mathematical formula providing the target pressure may be expressed as:

where;

p_target - target pressure,

P_engine - current engine power developed by the ICE, and

x - fixed factor dependent on the relevant type of engine.

[0041] As mentioned above, other components or functions of the ICE 30 may require a certain minimum fluid pressure. Thus, a boundary condition for a minimum target pressure may be set in the control unit 40.

[0042] The current engine power developed by the ICE 30 may be measured or calculated by the control unit 40 or any other suitable control unit related to the ICE 30. For instance, the current engine power developed by the ICE 30 may be calculated from the current fuel consumption of the ICE 30, or the current fuel consumption of the ICE 30 may be an indirect measure of the current engine power developed by the ICE 30. Accordingly, the current engine power developed by the ICE may be the actual current developed engine power, measured or calculated, or a different parameter directly dependent or related to the currently developed engine power, such e.g. the fuel consumption of the ICE, or the torque developed by the ICE 30.

[0043] According to some embodiments it may suffice to use only the current engine power developed by the ICE 30 as the operational parameter as a basis for controlling the fluid pump 34. A sufficient cleaning of the crankcase gas may be achieved while energy may be saved.

[0044] According to some embodiments, the at least one operational parameter comprises a current fuel consumption of the ICE 30.

[0045] According to some embodiments, the current engine power developed by the ICE 30, and/or the fuel consumption of the ICE 30, may be combined with one or more further operational parameters as a basis for controlling the fluid pump 34.

[0046] For instance, according to some embodiments, the at least one operational parameter may comprise a current rotational speed of the internal combustion engine 30. In this manner, the control of the fluid pump 34 towards the target pressure may be based also on the current rotational speed of the ICE 30. Namely, the amount of crankcase gas produced by the ICE 30 may vary not only in relation to the developed engine power, but also in relation to the rotational speed.

[0047] As mentioned above, the amount of crankcase gas produced by an ICE varies between different engine types. Generally, low developed engine power and low rotational speed produce low amounts of crankcase gas, while high developed engine power and high rotational speed produce high amounts of crankcase gas.

[0048] Fig. 3 shows a diagram providing a schematic example of the amount of crankcase gas produced from an ICE. The power ranges of the ICE (kW) at different rotational speeds of the ICE (RPM) are shown by the area covered by the different graphs. The graphs delimit areas which represent different amounts of crankcase gas produced. There are four larger areas representing a crankcase gas flow of 400 I/min, 300 I/min, 200 I/min, and 100 I/min, respectively. Also, there is a local variation within the 200 I/min area. Namely, within a limited area in the higher RPM range, there is a crankcase gas flow of 300 I/min.

[0049] Accordingly, in embodiments wherein the control of the fluid pump 34 is based on the at least one operational parameter comprising both the currently developed engine power and the current rotational speed of the ICE 30, a lookup table may be utilised for providing the relevant target pressure for a particular combination of power and rotational speed values.

[0050] Again, referring to Figs. 1 and 2, according to embodiments, the at least one operational parameter of the internal combustion engine 30 may further comprises at least one of:

• a current fluid temperature of the internal combustion engine,
• a current crankcase gas pressure level,
• a total internal combustion engine operating time, and
• a presence of a compressor load on the internal combustion engine.

[0051] By taking at least one of the above mentioned operational parameters of the ICE 30 into account, a relevant target pressure may be further tuned in order to provide a thorough control of the fluid pump 34.

• The fluid temperature may provide a measure of the operating temperature of the ICE 30, which may affect the amount of crankcase gas e.g. due to clearances in the ICE 30 being devised for the operating temperature. Accordingly, the ICE 30 may comprise a temperature sensor 44 for measuring a fluid temperature, such as a lubricating oil or coolant temperature of the ICE 30.
• The crankcase gas pressure level may be used as an indication of the amount of crankcase gas produced in the ICE 30. Accordingly, the ICE 30 may comprise a pressure sensor 46 for measuring a gas pressure in the crankcase 32. The crankcase gas pressure level may be used as an indication of the pumping capability of the centrifugal separator 20.
• The total ICE operating time may affect the amount of crankcase gas produced by the ICE 30. Accordingly, the control unit 40 may keep track of the total operating time of the ICE 30.

[0052] The total ICE operating time is counted from the first time the ICE 30 is started and is incremented while the ICE is operated/running.

• The presence of the compressor load on the ICE 30 may provide a higher load on the ICE 30. A relevant compressor may be a brake compressor 48 for providing pressurised air to a brake system of a vehicle, aboard which the ICE 30 is arranged. Accordingly, the control unit 40 may keep track of when a compressor 48 is in operation and when it is not in operation.

[0053] According to embodiments, the target pressure may be adjusted with a fixed factor in case at least one of:

• the current fluid temperature is below a threshold temperature level,
• the current crankcase gas pressure level is above a threshold pressure level,
• the total internal combustion engine operating time is below a threshold operating time, and
• the presence of the compressor load on the internal combustion engine.

[0054] The state of certain operational parameters of the ICE 30 may affect the amount of crankcase gas produced in the ICE 30. One way of taking account of such operational parameters may be to increase the target pressure with a fixed factor, f. The same fixed factor may be used for each operational parameter as well as for combinations of operational parameters. Alternatively, different fixed factors may be used for different operational parameters or for different combinations of parameters.

[0055] For instance, a mathematical formula providing the adjusted target pressure may be expressed as:

where;

p_{target new} - adjusted target pressure,

p_target - target pressure before adjustment, and

f - fixed factor.

[0056] Mentioned purely as an example, the fixed factor, f may be within a range of 1.1 - 1.5, such as e.g. 1.25.

[0057] A different example of, a mathematical formula providing the adjusted target pressure may be expressed as:

where instead;
f - fixed pressure value.

[0058] Mentioned purely as an example the fixed factor, f may be with a range of 0.1 - 3 bar, such as e.g. 1 bar.

[0059] In embodiments where a different parameter than the target pressure is utilised for controlling the fluid pump 34, such as e.g. the target rotational speed of the centrifugal rotor 4, the relevant parameter may be adjusted with the fixed factor.

[0060] The following are examples of the operational parameters above:

• The threshold temperature may be 90 degrees Celsius, which may be a proper operating temperature of the ICE 30. Accordingly, if the current fluid temperature is below 90 degrees Celsius, the target pressure is adjusted with the fixed factor in order to compensate for any increase in crankcase gas caused by a low ICE temperature, in order to raise the rotational speed of the centrifugal rotor 4.
• The threshold pressure level may be 0 kPa. The threshold pressure level is in this case a pressure difference between the inside of the crankcase 32 and the ambient pressure outside the ICE 30. An increased crankcase gas production in the ICE 30 or an improper functioning of the centrifugal separator 20 may cause an increase of the crankcase pressure above the threshold pressure level. Accordingly, if the current crankcase gas pressure level is above 0 kPa, the target pressure is adjusted with a fixed factor to compensate for the increased crankcase pressure. As mentioned above, the cause of the increased crankcase pressure may be a higher than expected production of crankcase gas in the ICE 30, or a decreased pumping capability of the centrifugal separator 20, both of which may be, at least temporarily, remedied by increasing the target pressure with the fixed factor, in order to raise the rotational speed of the centrifugal rotor 4. The actual crankcase gas pressure may fluctuate. Thus, an average value of the crankcase gas pressure over a time period may be utilised for determining the pressure difference between the inside of the crankcase 32 and the ambient pressure outside the ICE 30. Adjustment of the target pressure with the fixed factor may be stopped when the current crankcase gas pressure level is below the threshold pressure level. A hysteresis may be applied to prevent continuous switching between use of the fixed factor and non-use of the fixed factor.
• The threshold operating time of the ICE 30 may be 100 hours. This may be considered an adequate time period for running in an ICE. Before the ICE 30 is properly run in, the amount of crankcase gas may be increased when compared to after the running in period has been completed. Accordingly, if the current operating time is below 100 hours, the target pressure is adjusted with a fixed factor in order to compensate for the low operating time, in order to raise the rotational speed of the centrifugal rotor 4.
• If there is a presence of the compressor load on the ICE 30, the target pressure may be adjusted with a fixed factor in order to compensate for a higher load on the ICE, which may cause an increased amount of crankcase gas. Once the compressor load is removed, a target pressure without compensation with the fixed factor may be used again.

[0061] According to some embodiments, the ICE 30 may comprise a pressure sensor 42 configured for measuring a current pressure of the pressurised fluid. The pressure sensor 42 is electronically connected to the control unit 40. Thus, the control unit 40 may control the fluid pump 34 to regulate the pressure of the pressurised fluid from the pressure level measured by the pressure sensor 42 towards the target pressure. The pressure sensor 42 measures the current pressure of the pressurised fluid at a fluid outlet of the fluid pump 34. The control unit 40 may utilise the measured current pressure as a feedback for controlling the pressure towards the target pressure. A control algorithm such as e.g. a PID algorithm may be utilised by the control unit 40.

[0062] According to some embodiments, the centrifugal separator 20 may comprise a rotational speed sensor 50. The rotational speed sensor 50 is electrically connected to the control unit 40. The control unit 40 is configured to determine a current rotational speed of the centrifugal rotor 4 via the rotational speed sensor 50. In this manner, the control unit 40 may control the fluid pump 34 to regulate the pressure of the pressurised fluid towards the target pressure utilising the measured rotational speed of the centrifugal rotor 4. In such embodiments, the pressure of the pressurised fluid may not have to be measured. The current rotational speed of the centrifugal rotor 4 forms an indicator of the current pressure of the pressurised fluid. The control unit 40 may utilise the measured rotational speed as a feedback for controlling the fluid pump 34 towards the target pressure. Since, the target pressure corresponds to a target rotational speed of the centrifugal rotor 4, the control unit 40 may control the rotational speed of the centrifugal rotor 4 towards the target rotational speed. Again, a control algorithm such as e.g. a PID algorithm may be utilised by the control unit 40.

[0063] Fig. 4 schematically illustrates embodiments of a control system 52 of an ICE. The ICE may be an ICE 30 as discussed above with reference to Figs. 1 - 3. The control system 52 comprises the control unit 40 and one or more of the sensors 42, 44, 46, 50 discussed above. The control unit 40 may also be referred to as and ECU, Engine Control Unit.

[0064] The control unit 40 comprises a calculation unit 54 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 unit 40 comprises a memory unit 56. The calculation unit 54 is connected to the memory unit 56, which provides the calculation unit 54 with, for example, programme code, and/or stored data, and/or one or more lookup tables, which the calculation unit 54 needs to enable it to do calculations, and/or control devices such as the fluid pump 34. The calculation unit 54 is also adapted to storing partial or final results of calculations in the memory unit 56. The memory unit 56 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 56 may comprise integrated circuits comprising silicon-based transistors. The memory unit 56 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.

[0065] The control unit 40 is further provided with devices 58, 60 for receiving and sending input and output signals, respectively. These input and output signals may comprise waveforms, pulses or other attributes which the devices 58, 60 can handle. The input signals are supplied from the device 58 for receiving input signals to the calculation unit 54 in a format processable by the calculation unit 54. Similarly, the calculation unit 54 supplies data in a suitable format to the device 60 for sending output signals. The device 60 for sending output signals is arranged to send e.g. calculation results, such as control instructions, from the calculation unit 54 to other parts of the control system 52. Each of the connections to the respective devices for receiving and sending input and output signals may take the form of one or more forms selected 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.

[0066] The control system 52 may comprise one or more of sensors which are connected to the device 58 for receiving input signals, such as one or more of the above discussed pressure sensor 42, temperature sensor 44, pressure sensor 46, and/or rotational speed sensor 50. The device 60 for sending output signals is connected to the fluid pump 34 for sending control signals to the fluid pump 34. Thus, the control unit 40 may regulate the fluid pump 34 towards the target pressure.

[0067] The control system 52 may comprise a communication bus system consisting of one or more communication buses for connecting the control unit 40 with sensors and other control units, or controllers, of the ICE 30, or even of a vehicle which is driven by the ICE 30. For instance, the control unit 40 may receive data directly from a sensor via the communication bus.

[0068] Alternatively, the control unit 40 may receive data indirectly from a sensor, via a different control unit connected to the communication bus. Similarly, the control unit 40 may calculate data to be utilised in the control of the fluid pump 34, or the control unit 40 may receive data calculated in a different control unit via the communication bas to be utilised in the control of the fluid pump 34. For instance, a different control unit may calculate e.g., current engine power developed in the ICE 30, fuel consumption of the ICE 30, etc.

[0069] The control system 52 may comprise a number of control units taking care of one or more specific functions, or functions may be shared between two or more of the control units.

[0070] Fig. 5a schematically illustrates embodiments of a fluid pump 34 of the ICE 30 discussed above with reference to Figs. 1 and 2. The fluid pump 34 is a variable displacement pump. By varying the displacement of the variable displacement pump 34 the pressure of the pressurised fluid may be varied.

[0071] Variable displacement pumps are known as such and therefore, will only be briefly discussed in the following. However, the use of a variable displacement pump in connection with regulating the pressure of a pressurised fluid to be utilised in a drive arrangement of a centrifugal separator for cleaning of crankcase gas is not previously known, to the knowledge of the applicant. Example embodiments of variable displacement pumps are variable displacement vane pumps and axial piston pumps.

[0072] The variable displacement pump is directly driven by the ICE 30. For instance, a drive belt, a chain, or cog wheels may connect the crankshaft 31 of the ICE 30 with an axle 53 of the variable displacement pump. In the illustrated embodiments, the variable displacement pump is a variable displacement vane pump comprising a radially movable rotational centre of a rotor of the vane pump, as indicated by arrows 55. A mechanical setting of the fluid pump 34 for varying the displacement is thus, a position of the rotational centre of the rotor.

[0073] According to embodiments, the control unit 40 may be configured to control a displacement of the variable displacement pump based on the at least one operational parameter of the internal combustion engine 30. In this manner, the variable displacement pump may be regulated towards the target pressure. In embodiments comprising a variable displacement vane pump, the control unit 40 may control the position of the rotational centre of the rotor of the vane pump.

[0074] Fig. 5b schematically illustrates embodiments of a fluid pump 34 of the ICE 30 discussed above with reference to Figs. 1 and 2. The fluid pump 34 is a pump driven by an electric motor 62. Such a pump may for instance be a centrifugal pump or a fixed displacement pump.

[0075] Pumps driven by an electric motor are known as such and therefore, will only be briefly discussed in the following. However, the use of a pump driven by an electric motor in connection with regulating the pressure of a pressurised fluid to be utilised in a drive arrangement of a centrifugal separator for cleaning of crankcase gas is not previously known, to the knowledge of the applicant.

[0076] The pump driven by an electric motor 62 is indirectly driven by the ICE 30. Namely, the ICE 30 generates electric power via a generator 64, which in turn charges a battery 66. Electric energy from the battery 66 is utilised for driving the electric motor 62.

[0077] According to embodiments, the control unit 40 may be configured to control the rotational speed of the electric motor 62 based on the at least one operational parameter of the internal combustion engine 30. In this manner, the centrifugal pump driven by the electric motor 62 may be regulated towards the target pressure.

[0078] Fig. 6 illustrates embodiments of a method 100 of operating a centrifugal separator for cleaning of crankcase gas from an internal combustion engine. The ICE may be an ICE 30 as discussed above in connection with Figs. 1 - 5b. The internal combustion engine comprises a crankcase, a fluid pump, and the centrifugal separator. The centrifugal separator may be a centrifugal separator 20 as discussed above with reference to Fig. 2, and comprises a centrifugal rotor and a drive arrangement for driving the centrifugal rotor. The fluid pump is directly or indirectly driven by the internal combustion engine for providing a pressurised fluid. The fluid pump is configured to vary a pressure of the pressurised fluid independently of a rotational speed of the internal combustion engine. The method 100 comprises steps of:

• directing 102 the pressurised fluid towards an impeller of the drive arrangement, and
• regulating 104 the pressure of the pressurised fluid towards a target pressure based on at least one operational parameter of the internal combustion engine, the target pressure corresponding to a target rotational speed of the centrifugal rotor.

[0079] As discussed above, the centrifugal rotor is rotated at a sufficient speed for cleaning of currently produced crankcase gas in the ICE, but not at an unnecessarily high speed which would require more energy from the ICE. Thus, only a necessary amount of energy from the ICE is utilised for driving the centrifugal separator and the cleaning of crankcase gas.

[0080] According to embodiments, the method 100 further may comprise a step of:

• measuring 106 a current pressure of the pressurised fluid using a pressure sensor. In this manner, the pressure may be regulated towards the target pressure inter alia utilising the current pressure of the pressurised fluid, as discussed above with reference to Figs. 1 and 2.

[0081] According to embodiments, the method 100 further may comprise a step of:

• determining 108 a current rotational speed of the centrifugal rotor using a rotational speed sensor. In this manner, the pressure may be regulated towards the target pressure inter alia utilising the current rotational speed of the centrifugal rotor of the centrifugal separator, as discussed above with reference to Figs. 1 and 2.

[0082] According to embodiments, the method 100 further may comprise a step of:

• increasing 110 the target pressure with a fixed factor in case at least one of:

  a current fluid temperature is below a temperature threshold level,

  a current crankcase gas pressure level is above a pressure threshold level,

  a total internal combustion engine operating time is below a threshold operating time, and

  a presence of a compressor load on the internal combustion engine.

[0083] In this manner, account may be taken to the state of certain operational parameters of the ICE and how they may affect the amount of crankcase gas produced in the ICE. See further above with reference Figs. 1 and 2.

[0084] It is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended claims. A person skilled in the art will realize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the invention, as defined by the appended claims.

Claims

1. An internal combustion engine (30) comprising a crankcase (32), a fluid pump (34), and a centrifugal separator (20) for cleaning of crankcase gas, wherein

the fluid pump (34) is directly or indirectly driven by the internal combustion engine (30) for providing a pressurised fluid, and wherein

the centrifugal separator (20) comprises a centrifugal rotor (4) and a drive arrangement (10), the drive arrangement (10) being configured to utilise the pressurised fluid for driving the centrifugal rotor (4),

characterised in that

the fluid pump (34) is configured to vary a pressure of the pressurised fluid independently of a rotational speed of the internal combustion engine (30), and wherein

the internal combustion engine (30) comprises a control unit (40) configured to control the fluid pump (34) to regulate the pressure of the pressurised fluid towards a target pressure based on at least one operational parameter of the internal combustion engine (30), the target pressure corresponding to a target rotational speed of the centrifugal rotor (4).

2. The internal combustion engine (30) according to claim 1, comprising a pressure sensor (42) configured for measuring a current pressure of the pressurised fluid and being connected to the control unit (40).

3. The internal combustion engine (30) according to claim 1, wherein the centrifugal separator (20) comprises a rotational speed sensor (50) connected to the control unit (40), and wherein the control unit (40) is configured to determine a current rotational speed of the centrifugal rotor (4) via the rotational speed sensor (50).

4. The internal combustion engine (30) according to any one of the preceding claims, wherein the at least one operational parameter comprises a current engine power developed by the internal combustion engine (30).

5. The internal combustion engine (30) according to any one of the preceding claims, wherein the at least one operational parameter comprises a current fuel consumption of the internal combustion engine (30).

6. The internal combustion engine (30) according to claim 4 or 5, wherein the at least one operational parameter comprises a current rotational speed of the internal combustion engine (30).

7. The internal combustion engine (30) according to any one of claims 4-6, wherein the at least one operational parameter of the internal combustion engine (30) further comprises at least one of:

a current fluid temperature of the internal combustion engine (30),

a current crankcase gas pressure level,

a total internal combustion engine operating time, and

a presence of a compressor load on the internal combustion engine (30).

8. The internal combustion engine (30) according to claim 7, wherein the target pressure is adjusted with a fixed factor in case at least one of:

the current fluid temperature is below a threshold temperature level,

the current crankcase gas pressure level is above a threshold pressure level,

the total internal combustion engine operating time is below a threshold operating time, and

the presence of the compressor load on the internal combustion engine (30).

9. The internal combustion engine (30) according to any one of the preceding claims, wherein the fluid pump (34) is a variable displacement pump.

10. The internal combustion engine (30) according to claim 9, wherein the control unit (40) is configured to control a displacement of the variable displacement pump based on the at least one operational parameter of the internal combustion engine (30).

11. The internal combustion engine (30) according to any one of claims 1 - 8, wherein the fluid pump (34) is a pump driven by an electric motor (62).

12. The internal combustion engine (30) according to claim 11, wherein the control unit (40) is configured to control the rotational speed of the electric motor (62) based on the at least one operational parameter of the internal combustion engine (30).

13. A method (100) of operating a centrifugal separator (20) for cleaning of crankcase gas from an internal combustion engine (30), the internal combustion engine (30) comprising a crankcase (32), a fluid pump (34), and the centrifugal separator (20), wherein

the fluid pump (34) is directly or indirectly driven by the internal combustion engine (30) for providing a pressurised fluid, wherein

the centrifugal separator (20) comprises a centrifugal rotor (4) and a drive arrangement (10) for driving the centrifugal rotor (4), and wherein

the fluid pump (34) is configured to vary a pressure of the pressurised fluid independently of a rotational speed of the internal combustion engine (30),

the method (100) comprising steps of:

- directing (102) the pressurised fluid towards an impeller of the drive arrangement (10), and

- regulating (104) the pressure of the pressurised fluid towards a target pressure based on at least one operational parameter of the internal combustion engine (30), the target pressure corresponding to a target rotational speed of the centrifugal rotor (4).

14. The method (100) according to claim 13, further comprising a step of:

- measuring (106) a current pressure of the pressurised fluid using a pressure sensor (42).

15. The method (100) according to claim 13, further comprising a step of:

- determining (108) a current rotational speed of the centrifugal rotor (4) using a rotational speed sensor (50).

16. The method (100) according to any one of claims 13 - 15, further comprising a step of:

- increasing (110) the target pressure with a fixed factor in case at least one of:

a current fluid temperature is below a temperature threshold level,

a current crankcase gas pressure level is above a pressure threshold level,

a total internal combustion engine operating time is below a threshold operating time, and

a presence of a compressor load on the internal combustion engine.

Drawing