Degassing system for engine, vehicle and associated method

Abstract

A degassing system (4) for a dihydrogen internal combustion engine (3), the engine (3) comprising a cylinder head and a crankcase comprising an oil sump, is proposed. The degassing system comprises: - an oil regulation and separation device (28) comprising an inlet (29) configured to be connected to the cylinder head, a first outlet (30) and a second outlet (31) configured to be connected to the cylinder head, and - a Venturi device (35) comprising a suction inlet (36) connected to the first outlet of the oil regulation and separation device, a high-pressure inlet (37) and an exhaust outlet (38), the Venturi device (35) being configured to suction through the oil regulation and separation device (28) a first fluid comprising gaseous dihydrogen and oil droplets present in the cylinder head.

Description

[0001] DESCRIPTION

[0002] TITLE : Degassing system for engine, vehicle and associated method

[0003] The present invention relates to the degassing of an internal combustion engine of the spark-ignition type operating on dihydrogen.

[0004] The present invention relates more particularly to a degassing system for a dihydrogen internal combustion engine, a motor vehicle comprising a dihydrogen internal combustion engine and such a degassing system, and a degassing method using such a system.

[0005] A motor vehicle can be equipped with an internal combustion engine.

[0006] The operation of an internal combustion engine generates leakage of unburnt combustion gases escaping from the combustion chambers through the piston rings at the bottom of the engine block, below the piston crowns, and then towards the engine crankcase, more precisely in a lower engine crankcase mounted below the engine block and comprising, in particular, at its lower part, an oil sump, i.e. a volume of engine lubricating oil. These gases are known as crankcase gases or blow-by gases .

[0007] Unburnt combustion gases then accumulate in the engine crankcase and include unburnt fuel in gaseous form and oil droplets resulting from contact of the unburnt combustion gases with engine parts lubricated by engine oil.

[0008] Unburnt combustion gases must be evacuated from the crankcase and recycled in the engine.

[0009] The crankcase is also supplied with filtered air at atmospheric pressure.

[0010] It is necessary to de-oil the unburnt combustion gases by separating the oil droplets from the gaseous fuel before reintroducing the gaseous fuel into the engine's combustion chambers.

[0011] The unburnt gases are treated by an oil separator, which mechanically separates the gaseous fuel from the oil droplets. When the internal combustion engine is fuelled with petrol, the unburnt gases accumulated in the engine crankcase are not likely to ignite.

[0012] However, when the internal combustion engine is fuelled by dihydrogen, the unburnt combustion gases include gaseous dihydrogen and oil droplets .

[0013] It is known that dihydrogen is extremely flammable when its volume concentration exceeds 4%, so it is necessary to lower the volume concentration of the dihydrogen trapped in the engine crankcase to prevent ignition of the dihydrogen.

[0014] It is known to add a pump to remove unburnt combustion gases and deliver them to the oil separator. The volume of unburnt combustion gases removed by the pump is replaced in the crankcase by filtered air diluting the volume concentration of dihydrogen present in the engine crankcase.

[0015] However, installing the pump requires a lot of space in the vehicle's engine compartment.

[0016] In addition, as the pump is generally driven by an electric motor, it is necessary to provide an electrical power supply for the electric motor and to guarantee a high level of reliability for the pump and motor assembly, each of which has moving parts that can fail.

[0017] The aim of the invention is to overcome some or all of these disadvantages .

[0018] The invention relates to a degassing system for a dihydrogen internal combustion engine, the engine comprising a cylinder head and a crankcase comprising an oil sump .

[0019] The degassing system comprises:

[0020] - an oil regulation and separation device comprising an inlet configured to be connected to the cylinder head, a first outlet, and a second outlet configured to be connected to the cylinder head, and

[0021] - a Venturi device comprising a suction inlet connected to the first outlet of the oil regulation and separation device, a high-pressure inlet and an exhaust outlet. The Venturi device is configured to suction through the oil regulation and separation device a first fluid comprising gaseous dihydrogen and oil droplets present in the cylinder head when a second gaseous fluid flows from the high pressure inlet to the exhaust outlet, and the oil regulation and separation device is configured to separate the oil droplets and gaseous dihydrogen from the first fluid, and deliver the gaseous dihydrogen to the first outlet and liquid oil resulting from the separation process to the second outlet so that the oil flows into the oil sump.

[0022] Preferably, the engine comprises an air intake manifold, the first inlet of the oil regulation and separation device being configured for connection to the air intake manifold.

[0023] Advantageously, the oil regulation and separation device comprises an oil separator and a control valve connected in series .

[0024] Preferably, the control valve comprises a first connection connected to the inlet of the oil regulation and separation device and a second connection, and the oil separator comprises a first connection connected to the second connection of the control valve, a second connection connected to the first outlet and a third connection connected to the second outlet, the oil separator being configured to separate the oil droplets, on the one hand, and the oil vapours and dihydrogen, on the other hand, from the first fluid delivered by the control valve and to deliver the dihydrogen to the second connection and the oil to the third connection.

[0025] Advantageously, the oil separator comprises a first connection connected to the inlet of the oil regulation and separation device, a second connection and a third connection connected to the second outlet, the oil separator being configured to separate the oil droplets on the one hand, the second connection and a third connection connected to the second output, the oil separator being configured to separate the oil droplets, on the one hand, and the oil vapours and the dihydrogen, on the other hand, from the first fluid supplied by the input of the oil regulation and separation device and to supply the dihydrogen to the second connection and the oil to the third connection, and the control valve comprises a first connection connected to the second connection of the oil separator and a second connection connected to the first output of the oil regulation and separation device.

[0026] Preferably, the degassing system also comprises a pressure sensor configured to measure the pressure of the first fluid located in the crankcase above the oil sump and a dihydrogen sensor configured to measure the concentration of gaseous dihydrogen in the crankcase above the oil sump, and a processing unit configured to control the control valve on the basis of the measurements provided by the pressure sensor and the dihydrogen sensor.

[0027] Also proposed is a motor vehicle comprising a dihydrogen internal combustion engine comprising a cylinder head, an air intake manifold connected to the cylinder head and a crankcase comprising an oil sump.

[0028] The vehicle comprises a compression device comprising an inlet and an outlet connected to the air intake manifold, and being configured to compress the second gaseous fluid at the compression device inlet and deliver the compressed second gaseous fluid at the compression device outlet.

[0029] The vehicle comprises a degassing system as previously defined, the inlet of the oil regulation and separation device being connected to the cylinder head, the second outlet of the oil regulation and separation device being connected to the cylinder head, the first outlet of the oil regulation and separation device being connected to the suction inlet of the Venturi device, the high-pressure inlet of the Venturi device being connected to the outlet of the compression device and the exhaust outlet of the Venturi device being connected to the inlet of the compression device.

[0030] A method of degassing a dihydrogen internal combustion engine is also proposed, the engine comprising a cylinder head and a crankcase including an oil sump.

[0031] An inlet and a second outlet of an oil regulation and separation device are connected to the cylinder head. A suction inlet of a Venturi device is connected to a first outlet of the oil regulation and separation device, the Venturi device further comprising a high-pressure inlet and an exhaust outlet.

[0032] The method comprises:

[0033] - supplying the high-pressure inlet with a second compressed gaseous fluid so that the second gaseous fluid flows from the high- pressure inlet to the exhaust outlet in order to suction a first fluid comprising gaseous dihydrogen and oil droplets present in the cylinder head through the oil regulation and separation device,

[0034] - separation of oil droplets, on the one hand, and oil vapours and gaseous dihydrogen, on the other hand, of the first fluid in the oil regulation and separation device when the second gaseous fluid is supplied to the high-pressure inlet,

[0035] - delivery of gaseous dihydrogen to the first outlet, and

[0036] - delivery of liquid oil resulting from the separation at the second outlet so that the oil flows into the oil sump.

[0037] Preferably, the oil regulation and separation device comprises an oil separator and a control valve connected in series.

[0038] The method comprises controlling the control valve so that the difference between pressure in the crankcase and atmospheric pressure is less than a predetermined negative threshold and so that the volume concentration of dihydrogen in the crankcase is less than a predetermined value.

[0039] Further aims, characteristics and advantages of the invention will become apparent from the following description, which is given solely by way of non-limiting example, and is made with reference to the appended drawings in which:

[0040] [Fig 1 ] schematically illustrates an example of a motor vehicle according to the invention;

[0041] [Fig 2] schematically illustrates an example of a vehicle engine;

[0042] [Fig 3] schematically illustrates an example of an engine compartment according to the invention;

[0043] [Fig 4] schematically illustrates a first example of the implementation of the oil regulation and separation device according to the invention, and

[0044] [Fig 5] schematically illustrates a second example of the implementation of an oil regulation and separation device according to the invention.

[0045] Figure 1 schematically illustrates an example of a motor vehicle 1.

[0046] Vehicle 1 comprises an engine compartment 2 with a dihydrogen internal combustion engine 3 and an engine degassing system 4.

[0047] The engine 3 propels the vehicle 1.

[0048] Figure 2 shows a cross-section of the engine 3

[0049] Engine 3 comprises four identical cylinders 5.

[0050] Of course, the engine 3 may comprise more than four cylinders or less than four cylinders, with the engine 3 comprising at least one cylinder.

[0051] The engine 3 comprises an engine block 6, or crankcase 6, housing the cylinders 5.

[0052] The engine block 6 is surmounted by a cylinder head 7, and a lower crankcase, containing an oil sump 8 with the lubricating oil for the engine 3, is mounted at the bottom of the engine block. In the following, the term "crankcase" will refer more specifically to the lower crankcase in its entirety, the expression "oil sump" referring to the volume of oil contained in the bottom of the lower crankcase.

[0053] The oil sump 8 is located in the lower part of the engine 3 and the cylinder head 7 is located in the upper part of the engine 3 so that oil flows from the cylinder head 7 to the oil sump 8 under the effect of gravity.

[0054] A piston 9 is inserted into each cylinder 5 and comprises rings

[0055] 10. Each piston 9 is connected to a crankshaft 1 1 via a connecting rod 12.

[0056] Each cylinder 5 is also connected to a gas inlet duct 13 and an exhaust duct 14.

[0057] The cylinder head 7 comprises a first connection 15 and a second connection 16.

[0058] The crankcase includes a connection 17 opening above the oil level, i.e. above the oil sump 8.

[0059] The dihydrogen-powered engine 3 is a four-stroke spark-ignition engine based on the Beau de Rochas cycle.

[0060] When the engine 3 is running, a first fluid (represented by arrows) escapes from the cylinders 5 via the piston rings 10 and accumulates in the bottom of the engine block 6 and in the crankcase comprising the oil sump 8. This first fluid also accumulates in the cylinder head 7.

[0061] The first fluid comprises unburnt gases comprising gaseous dihydrogen and oil droplets, and may also comprise oil vapours in small quantities .

[0062] Figure 3 shows an example of the engine compartment 2.

[0063] The engine compartment 2 also comprises an air inlet 20, an air filter 21 , a compression device 22 for compressing a second gaseous fluid, a throttle body 23, an intake manifold 24, an exhaust manifold 25 and an exhaust gas outlet 26.

[0064] The compression device 22 comprises, for example, at least one turbocharger compressor and / or a mechanical compressor driven by the engine 3 and compressing the second gaseous fluid comprising air filtered by the air filter 20.

[0065] An inlet of the air filter 21 is connected to the air inlet 20 and an outlet of the air filter 21 is connected to an inlet of the compression device 22.

[0066] An output from the compression device 22 is connected to a connection on the throttle body 23 and an output from the throttle body 23 is connected to the intake manifold 24. The intake manifold 24 is also connected to the intake ducts 13 of the cylinders 4.

[0067] The exhaust manifold 25 connects the exhaust ducts 14 of the cylinders 4 to the exhaust gas outlet 26.

[0068] The exhaust outlet 26 is connected, for example, to an exhaust gas after-treatment device (not shown) .

[0069] The air filter outlet 21 is also connected to the crankcase connection 17 to inject filtered air into the crankcase above the oil sump 8, i.e. above the oil level, for example via a first non-return valve 27 so that oil does not escape from the engine 3 via the connection 17.

[0070] The degassing system 4 comprises an oil regulation and separation device 28 comprising an inlet 29 connected to the first connection 15 of the cylinder head 7, a first outlet 30, and a second outlet 31 connected to the second connection 16 of the cylinder head 7 for example via a second non-return valve 32.

[0071] The second non-return valve 32 is dimensioned so that when a liquid flows from the second outlet 31 , said valve 32 opens so that the liquid flows into the second connection 16.

[0072] The device 28 is able to separate the oil droplets, on the one hand, and the oil vapours and gaseous dihydrogen, on the other, of the first fluid flowing over the first connection 15 of the cylinder head 7, and deliver the dihydrogen to the first outlet 30 and the oil to the second outlet 31 so that the oil flows into the oil sump 8.

[0073] Device 28 comprises a control valve 33 and an oil separator 34 connected in series .

[0074] The oil separator 34 comprises an oil separator known from the state of the art comprising, for example, baffles .

[0075] The degassing system 4 also comprises a Venturi device 35 having a suction inlet 36 connected to the first outlet 30 of the oil regulation and separation device 28, a high-pressure inlet 37 connected to the outlet of the compression device 22 and an exhaust outlet 38 connected to the inlet of the compression device 22. The first outlet 30 of the device 28 is also connected to the intake manifold 24, between the throttle body 23 and said manifold 24, for example via a third non-return valve 39.

[0076] The third non-return valve 39 is dimensioned so that when the pressure on the first outlet 30 of the device 28 is greater than the pressure in the intake manifold 24 by a predetermined value, for example a few hundred millibars, the third non-return valve 39 opens to allow a gaseous fluid to pass from the first outlet 30 of the device 28 into the intake manifold 24.

[0077] Alternatively, the first output 30 of the device 28 is not connected to the intake manifold 24.

[0078] The degassing system 4 also comprises a pressure sensor 40 for measuring the pressure of the first fluid located in the crankcase above the oil sump 8 , a dihydrogen sensor 41 for measuring the concentration of gaseous dihydrogen in the crankcase above the oil sump 8 or alternatively in the top of the engine at the level of the cylinder head 7 , and a processing unit 42 capable of controlling the control valve 33 on the basis of the measurements provided by the pressure sensor 40 and the dihydrogen sensor 41.

[0079] The high-pressure inlet 37 is connected to the outlet of the compression device 22, for example via a fourth non-return valve 43.

[0080] The fourth non-return valve 43 is dimensioned so that, when the pressure at the outlet of the compression device 22 is greater than the pressure at the inlet of the compression device 22, for example by more than one bar, the fourth non-return valve 43 opens to allow the second fluid to pass into the Venturi device 35.

[0081] Figure 4 illustrates a first example of the implementation of the oil regulation and separation device 28 comprising the valve 33 and the oil separator 34.

[0082] The valve 33 comprises a first connection 43 connected to the inlet 29 of the device 28 and a second connection 44 connected to a first connection 45 of the oil separator 34.

[0083] The valve 33 comprises a control input 46 connected to the processing unit 42. The oil separator 34 also comprises a second connection 47 connected to the first outlet 30 of the device 28 and a third connection 48 connected to the second outlet 31 of the device 28.

[0084] Figure 5 illustrates a second example of the implementation of the oil regulation and separation device 28, comprising the valve 33 and the oil separator 34.

[0085] The first connection 45 of the oil separator 34 is connected to the inlet 29 of the device 28, the second connection 47 of the oil separator 34 is connected to the first connection 43 of the valve 33 and the third connection 48 of the oil separator 34 is connected to the second outlet 31 of the device 28.

[0086] The second connection 44 of the valve 33 is connected to the first output 30 of the device 28 and the control input 46 is connected to the processing unit 42.

[0087] An example of an engine 3 degassing process using the degassing system 4 is now described.

[0088] When the engine 3 is running, air from outside the vehicle 1 flows into the air inlet 20 and is filtered by the air filter 21.

[0089] The air filtered by the air filter 20 is compressed by the compression device 22 and injected into the engine 3 via the throttle body 23 and the intake manifold 24.

[0090] The compression device 22 and throttle body 23 are controlled by the control system or processing unit 42 to respond in particular to the request of the driver of the vehicle 1 expressed by the depression of the accelerator pedal, to regulate the mechanical power delivered by the engine 3 propelling the vehicle 1.

[0091] P l is the air pressure at the inlet of the compression device 22, generally equal to or close to atmospheric pressure, i.e. 1 bar, P2 is the pressure at the outlet of the compression device 22 and P3 is the pressure in the intake manifold 24.

[0092] Compression device 22 compresses the filtered air and delivers the second compressed fluid (compressed filtered air) at its outlet so that pressure P2 is greater than pressure P l , pressure P2 being equal to 2 bar for example. As the pressure P2 is greater than the pressure P l , the fourth non-return valve 43 opens and the second compressed fluid flows from the high-pressure inlet 37 to the exhaust outlet 38 of the Venturi device 35, creating a negative pressure at the suction inlet 36.

[0093] Under the effect of the negative pressure created at the suction inlet 36 by the passage of the second compressed fluid through the Venturi device 35, the first fluid comprising gaseous dihydrogen and oil vapours present in the cylinder head 7 is suctioned into the device 28.

[0094] The first fluid suctioned in by the device 28 creates a negative pressure in the bottom of the engine block 6 and in the crankcase, so that the first non-return valve 27 opens and lets filtered air into the crankcase, above the oil sump 8 , allowing the volume concentration of dihydrogen in the crankcase to be diluted.

[0095] The processing unit 42 controls the valve 33 on the basis of the measurements delivered by the sensors 40, 41 so that the difference between the pressure in the crankcase above the oil sump 8 and atmospheric pressure is less than a predetermined negative threshold, for example 50 millibars, and so that the volume concentration of dihydrogen in the crankcase is less than a predetermined value, for example 2% .

[0096] As the difference between the pressure in the crankcase and atmospheric pressure is less than the predetermined negative threshold, the crankcase is at negative pressure relative to atmospheric pressure so that any dihydrogen contained in the engine 3 does not escape into the engine compartment 2.

[0097] The predetermined value is chosen so that the volume concentration of dihydrogen is less than the minimum concentration allowing the dihydrogen to be flammable, for example 4% .

[0098] The oil separator 34 of device 28 mechanically separates the oil droplets on the one hand, and the oil vapours and gaseous dihydrogen on the other, of the first fluid, delivers gaseous dihydrogen to the first outlet 30, and delivers the liquid oil resulting from the separation to the second outlet 31 . When the system 4 comprises the connection between the outlet 30 of the device 28 and the intake manifold 24, and the pressure difference between the pressure P2 and the pressure P l is not sufficient to create a negative pressure in the Venturi device 35 enabling the first fluid to be suctioned into the device 28, the negative pressure created in the intake manifold 24 by the circulation of compressed filtered air in the intake ducts 13 enables the third valve 39 to be opened so that the dihydrogen delivered by the device 28 is injected into the intake manifold 24.

[0099] When the system 4 does not comprise the connection between the outlet 30 of the device 28 and the intake manifold 24, the compression device 22 is dimensioned so that the pressure difference between the pressure P2 and the pressure P l is sufficient to create a negative pressure in the Venturi device 35 enabling the first fluid to be suctioned into the device 28.

[0100] Unlike the use of a pump dedicated to degassing the crankcase 5 of the engine 3 known from the state of the art, the degassing system 4 uses the Venturi device 35.

[0101] The space required to install the Venturi device 35 in the engine compartment 2 is reduced compared to the installation of the pump dedicated to crankcase degassing 5, making it easier to integrate the degassing system 4 in the engine compartment 2.

[0102] In addition, the Venturi device 35 is economically more advantageous (less expensive) than the pump and comprises no moving parts, so that the reliability and safety of the degassing system 4 are higher than those of a degassing system comprising the pump known in the state of the art.

Claims

CLAIMS1. Degassing system (4) for a dihydrogen internal combustion engine (3), the engine (3) comprising a cylinder head (7) and a crankcase comprising an oil sump (8), characterised in that the degassing system comprises : an oil regulation and separation device (28) comprising an inlet (29) configured to be connected to the cylinder head, a first outlet (30), and a second outlet (31 ) configured to be connected to the cylinder head, and a Venturi device (35) comprising a suction inlet (36) connected to the first outlet of the oil regulation and separation device, a high-pressure inlet (37) and an exhaust outlet (38), the Venturi device (35) being configured to suction through the oil regulation and separation device (28) a first fluid comprising gaseous dihydrogen and oil droplets present in the cylinder head (7) when a second gaseous fluid flows from the high pressure inlet (37) to the exhaust outlet (38), and the oil regulation and separation device (28) being configured to separate the oil droplets and the gaseous dihydrogen of the first fluid, and deliver the gaseous dihydrogen to the first outlet (30) and the liquid oil resulting from the separation process to the second outlet (31 ) so that the oil flows into the oil sump.

2. System according to claim 1 , wherein the engine (3) comprises an air intake manifold (24), the first inlet (31 ) of the oil regulation and separation device (28) being configured for connection to the air intake manifold.

3. System according to claim 1 or 2, wherein the oil regulation and separation device (28) comprises an oil separator (34) and a control valve (33) connected in series .

4. System according to claim 3, wherein the control valve (33) comprises a first connection (43) connected to the inlet (29) of the oil regulation and separation device (28) and a second connection (44), and the oil separator (34) comprises a first connection (45) connected to the second connection (44) of the control valve, a second connection (47) connected to the first outlet (30) and a third connection (48) connected to the second outlet (31 ), the oil separator (34) being configured to separate the oil droplets, on the one hand, and the oil vapours and the dihydrogen, on the other hand, of the first fluid delivered by the controlvalve, and to deliver the dihydrogen to the second connection and the oil to the third connection.

5. System according to claim 3, in which the oil separator (34) comprises a first connection (45) connected to the inlet (29) of the oil regulation and separation device (28), a second connection (47) and a third connection (48) connected to the second outlet (31 ), the oil separator (34) being configured to separate the oil droplets on the one hand, and on the other hand the oil vapours and the dihydrogen of the first fluid delivered by the inlet (29) of the oil regulation and separation device (28), and deliver the dihydrogen to the second connection (30) and the oil to the third connection (48), and the control valve (33) comprises a first connection (43) connected to the second connection of the oil separator and a second connection (44) connected to the first outlet of the oil regulation and separation device.

6. System according to one of claims 3 to 5, further comprising a pressure sensor (40) configured to measure the pressure of the first fluid located in the crankcase above the oil sump (8) and a dihydrogen sensor (41 ) configured to measure the concentration of gaseous dihydrogen in the crankcase above the oil sump (8), and a processing unit (42) configured to control the control valve (33) on the basis of the measurements delivered by the pressure sensor and the dihydrogen sensor.

7. Motor vehicle ( 1 ) comprising a dihydrogen internal combustion engine (3) comprising a cylinder head (7), an air intake manifold (24) connected to the cylinder head (7) and a crankcase comprising an oil sump (8), the vehicle comprising a compression device (22) comprising an inlet and an outlet connected to the air intake manifold (24) and being configured to compress the second gaseous fluid at the inlet of the compression device (22) and to deliver the compressed second gaseous fluid at the outlet of the compression device (22), the vehicle comprising a degassing system (4) according to one of claims 1 to 6, the inlet (29) of the oil regulation and separation device (28) being connected to the cylinder head (7), the second outlet (31 ) of the oil regulation and separation device being connected to the cylinder head, the first outlet (30) of the oil regulation and separation device being connected to the suction inlet (36) of the Venturi device (35), the high-pressure inlet (37) of the Venturi device being connected to the outlet of the compression device (22) and the exhaust outlet (38) of the Venturi device being connected to the inlet of the compression device.

8. Method for degassing a dihydrogen internal combustion engine (3), the engine (3) comprising a cylinder head (7) and a crankcase comprising an oil sump (8),• an inlet (29) and a second outlet (31 ) of an oil regulation and separation device (28) being connected to the cylinder head (7),• characterised in that a suction inlet (36) of a Venturi device (35) is connected to a first outlet (30) of the oil regulation and separation device (28), the Venturi device further comprising a high-pressure inlet (37) and an exhaust outlet (38), the method comprising: the high-pressure inlet (37) is supplied with a second compressed gaseous fluid so that the second gaseous fluid flows from the high- pressure inlet (37) towards the exhaust outlet (38) in order to suction, through the oil regulation and separation device (38), a first fluid comprising gaseous dihydrogen and oil droplets present in the cylinder head (7), separation of oil droplets, on the one hand, and oil vapours and gaseous dihydrogen, on the other hand, of the first fluid in the oil regulation and separation device (28) when the second gaseous fluid is fed to the high-pressure inlet, delivery of gaseous dihydrogen to the first outlet (30), and delivery of liquid oil resulting from the separation at the second outlet (31 ) so that the oil flows into the oil sump (7) .

9. Method for degassing according to claim 8, wherein the oil regulation and separation device (28) comprises an oil separator (34) and a control valve (33) connected in series, the method comprising controlling the control valve (33) so that the difference between pressure in the crankcase and atmospheric pressure is less than a predetermined negative threshold and so that the volume concentration of dihydrogen in the crankcase is less than a predetermined value.

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