Engine, vehicle and associated process degassing system

Abstract

A degassing system (4) for a hydrogen internal combustion engine (3) is proposed, the engine (3) comprising a cylinder head and a crankcase including an oil reservoir. The degassing system comprises: - an oil regulating and separation device (28) having 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) having a suction inlet (36) connected to the first outlet of the oil regulating and separation device, a high-pressure inlet (37) and an exhaust outlet (38), the Venturi device (35) being configured to draw through the oil regulating and separation device (28) a first fluid comprising gaseous hydrogen and oil droplets present in the cylinder head. Figure for the abstract: Fig 3

Description

Title of the invention: Degassing system for engine, vehicle and associated process

[0001] The present invention relates to the degassing of an internal combustion engine of the spark-ignition type operating on dihydrogen.

[0002] The present invention relates more particularly to a degassing system for a hydrogen internal combustion engine, a motor vehicle comprising a hydrogen internal combustion engine and such a degassing system, and a degassing process implementing such a system.

[0003] A motor vehicle can be equipped with an internal combustion engine.

[0004] The operation of the internal combustion engine generates leaks of unburned combustion gases escaping from the combustion chambers through piston rings in the lower part of the engine block, below the piston heads, and then into an engine crankcase, more precisely into a lower engine crankcase mounted below the engine block and including, in particular, at its lower part, an oil reservoir, i.e., a volume of engine lubricating oil. These gases are known as crankcase gases or "blow-by" gases, according to English terminology.

[0005] The unburned combustion gases then accumulate in the engine crankcase and include unburned fuel in gaseous form and oil droplets from the contact of the unburned combustion gases with engine parts lubricated by engine oil.

[0006] Unburned combustion gases must be evacuated from the crankcase and recycled into the engine.

[0007] The crankcase is further supplied at atmospheric pressure by filtered air.

[0008] It is necessary to de-oil the unburned combustion gases by separating the oil droplets and the fuel in gaseous form before reintroducing the fuel in gaseous form into the engine combustion chambers.

[0009] The unburned gases are treated by an oil separator ensuring the mechanical separation of the fuel in gaseous form and the oil droplets.

[0010] When the internal combustion engine is fueled with gasoline, the unburned gases accumulated in the engine crankcase are not likely to ignite.

[0011] However, when the internal combustion engine is fueled by dihydrogen, the unburned combustion gases include dihydrogen in gaseous form and oil droplets.

[0012] It is known that dihydrogen is extremely flammable when its volume concentration is greater than 4%, so it is necessary to lower the volume concentration of dihydrogen trapped in the engine casing to prevent the ignition of said dihydrogen.

[0013] It is known to add a pump to collect unburned combustion gases and deliver them to the oil separator. The volume of unburned combustion gases collected by the pump is replaced in the crankcase by filtered air, thus diluting the volumetric concentration of dihydrogen present in the engine crankcase.

[0014] However, the installation of the pump requires a significant amount of space in the vehicle's engine compartment.

[0015] In addition, since the pump is generally driven by an electric motor, it is necessary to provide an electrical supply for the electric motor and to guarantee a high level of reliability of the pump and motor assembly, each of which has moving parts that could fail.

[0016] The object of the invention is to overcome all or part of these drawbacks.

[0017] The invention relates to a degassing system for an internal combustion engine using dihydrogen, the engine includes a cylinder head and a crankcase containing an oil reservoir.

[0018] The degassing system comprises:

[0019] - an oil regulation and separation device comprising an inlet configured to be connected to the cylinder head, a first output, and a second output configured to be connected to the cylinder head, and

[0020] - 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.

[0021] The Venturi device is configured to draw through the oil regulating and separation device a first fluid containing 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 regulating and separation device is configured to separate the oil droplets and gaseous dihydrogen from the first fluid, and deliver the gaseous dihydrogen on the first outlet and liquid oil resulting from the separation process on the second outlet so that the oil flows into the oil tank.

[0022] Preferably, the engine includes an air intake manifold, the first inlet of the oil regulating and separation device being configured to be connected to the air intake manifold.

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

[0024] Preferably, the control valve includes a first connection connected to the inlet of the oil control and separation device and a second connection, and the oil separator includes 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 on the other hand the oil vapors and dihydrogen from the first fluid delivered by the control valve and deliver the dihydrogen on the second connection and the oil on the third connection.

[0025] Advantageously, the oil separator includes a first connection connected to the inlet of the oil regulating 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, and on the other hand the oil vapors and dihydrogen from the first fluid delivered by the inlet of the oil regulating and separation device and to deliver the dihydrogen on the second connection and the oil on the third connection, and the regulating valve includes a first connection connected to the second connection of the oil separator and a second connection connected to the first outlet of the oil regulating and separation device.

[0026] Preferably, the degassing system further comprises a pressure sensor configured to measure the pressure of the first fluid located in the crankcase above the oil tank and a dihydrogen sensor configured to measure the concentration of gaseous dihydrogen in the crankcase above the oil tank, and a processing unit configured to control the regulating valve from the measurements delivered by the pressure sensor and the dihydrogen sensor.

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

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

[0029] The vehicle includes a degassing system as defined above, the inlet of the oil regulating and separation device being connected to the cylinder head, the second outlet of the oil regulating and separation device being connected to the cylinder head, the first outlet of the oil regulating 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 output of the compression device and the exhaust output of the Venturi device being connected to the input of the compression device.

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

[0031] An inlet and a second outlet of an oil regulation and separation device are connected to the cylinder head.

[0032] 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.

[0033] The process comprises:

[0034] - a high-pressure inlet supplied by a second gaseous fluid compressed so that the second gaseous fluid flows from the high-pressure inlet to the exhaust outlet to draw, through the oil regulation and separation device, a first fluid containing gaseous dihydrogen and oil droplets present in the cylinder head,

[0035] - a separation of oil droplets on the one hand, and oil vapors on the other and of the gaseous dihydrogen from the first fluid in the oil regulation and separation device during the supply of the high-pressure inlet by the second gaseous fluid,

[0036] - a delivery of gaseous dihydrogen on the first outlet, and

[0037] - a delivery of liquid oil resulting from the separation on the second outlet of so that the oil flows into the oil tank.

[0038] Preferably, the oil regulation and separation device comprises an oil separator and a regulating valve connected in series.

[0039] The method includes a control of the regulating valve so that the difference between pressure in the crankcase and atmospheric pressure is less than a predetermined negative threshold and so that the volumetric concentration of dihydrogen in the crankcase is less than a predetermined value.

[0040] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0041] [Fig.1]

[0042] schematically illustrates an example of a motor vehicle according to the invention;

[0043] [Fig.2]

[0044] schematically illustrates an example of a vehicle engine;

[0045] [Fig.3]

[0046] schematically illustrates, for example, an example of the realization of an engine compartment according to the invention;

[0047] [Fig.4]

[0048] schematically illustrates a first example of an embodiment of the oil regulation and separation device according to the invention, and

[0049] [Fig.5]

[0050] schematically illustrates a second example of an embodiment of the oil regulation and separation device according to the invention.

[0051] Fig. 1 schematically illustrates an example of a motor vehicle.

[0052] The vehicle 1 includes an engine compartment 2 comprising a dihydrogen internal combustion engine 3 and an engine degassing system 4.

[0053] The engine 3 provides propulsion for the vehicle 1.

[0054] Figure 2 illustrates a cross-section of the engine 3

[0055] The engine 3 comprises four identical cylinders 5.

[0056] Of course, engine 2 may include more than four cylinders or fewer than four cylinders, engine 2 having at least one cylinder.

[0057] The engine 3 includes an engine block 6, or cylinder block 6 housing the cylinders 5.

[0058] The engine block 6 is surmounted by a cylinder head 7, and a lower crankcase, containing an oil reservoir 8 with the engine lubricating oil 3, is mounted to the lower part of the engine block. In the following, the term "crankcase" will refer more specifically to the lower crankcase as a whole, the expression "oil reservoir" referring to the volume of oil contained in the bottom of the lower crankcase.

[0059] The oil tank 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 tank 8 under the effect of gravity.

[0060] A piston 9 is inserted into each cylinder 5 and includes rings 10.

[0061] Each piston 9 is connected to a crankshaft 11 via a connecting rod 12.

[0062] Each cylinder 5 is further connected to an intake duct 13 and an exhaust duct 14 of gas.

[0063] The cylinder head 7 includes a first connection 15 and a second connection 16.

[0064] The crankcase includes a connection 17 opening above the oil level, i.e. above the oil tank 8.

[0065] The hydrogen-powered engine 3 is a four-stroke engine of the spark-ignition type, based on the Beau de Rochas cycle.

[0066] When the engine 3 is running, a first fluid (represented by arrows) escapes from the cylinders 5 through the segments 10 and accumulates in the bottom of the engine block 6 and in the crankcase including the oil reservoir 8. This first fluid also accumulates in the cylinder head 7.

[0067] The first fluid comprises unburned gases including gaseous dihydrogen and oil droplets, and may further comprise small amounts of oil vapors.

[0068] Fig. 3 illustrates an example of an embodiment of engine compartment 2.

[0069] The engine compartment 2 further includes 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.

[0070] The compression device 22 includes, 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.

[0071] 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.

[0072] An output of the compression device 22 is connected to a connection of the throttle body 23 and an output of the throttle body 23 is connected to the intake manifold 24.

[0073] The intake manifold 24 is further connected to the intake ports 13 of the cylinders 4.

[0074] The exhaust manifold 25 connects the exhaust ducts 14 of the cylinders 4 to the exhaust gas outlet 26.

[0075] The exhaust gas outlet 26 is for example connected to an exhaust gas aftertreatment device (not shown).

[0076] The outlet of the air filter 21 is further connected to the connection 17 of the crankcase to inject filtered air into the crankcase above the oil tank 8, i.e. above the oil level, for example via a first check valve 27 so that oil does not escape from the engine 3 through the connection 17.

[0077] The degassing system 4 includes an oil regulation and separation device 28 having 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 check valve 32.

[0078] The second check 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.

[0079] The device 28 is capable of separating the oil droplets on the one hand, and on the other hand the oil vapors and gaseous dihydrogen from the first fluid circulating on the first connection 15 of the cylinder head 7, and delivering the dihydrogen on the first outlet 30 and the oil on the second outlet 31 so that the oil flows into the oil tank 8.

[0080] The device 28 includes a regulating valve 33 and an oil separator 34 connected in series.

[0081] The oil separator 34 includes an oil separator known from the prior art comprising, for example, baffles.

[0082] The degassing system 4 further includes 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.

[0083] The first outlet 30 of the device 28 is further connected to the intake manifold 24, between the throttle body 23 and said manifold 24, for example via a third check valve 39.

[0084] The third check 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 check valve 39 opens to allow a gaseous fluid to pass from the first outlet 30 of the device 28 into the intake manifold 24.

[0085] Alternatively, the first outlet 30 of the device 28 is not connected to the intake manifold 24.

[0086] The degassing system 4 further comprises a pressure sensor 40 for measuring the pressure of the first fluid located in the crankcase above the oil tank 8, a dihydrogen sensor 41 for measuring the concentration of gaseous dihydrogen in the crankcase above the oil tank 8 or, alternatively, in the upper engine at the cylinder head 7, and a processing unit 42 capable of controlling the regulating valve 33 based on the measurements provided by the pressure sensor 40 and the dihydrogen sensor 41.

[0087] The high-pressure inlet 37 is connected to the outlet of the compression device 22, for example, via a fourth check valve 43.

[0088] The fourth check 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 check valve 43 opens to allow the second fluid to pass into the Venturi device 35.

[0089] Figure 4 illustrates a first example of the implementation of the regulation device 28 and oil separation unit comprising valve 33 and oil separator 34.

[0090] The valve 33 includes 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.

[0091] The valve 33 includes a control input 46 connected to the processing unit 42.

[0092] The oil separator 34 further includes a second connection 47 connected to the first output 30 of device 28 and a third connection 48 linked to the second output 31 of device 28.

[0093] Fig. 5 illustrates a second example of an embodiment of the oil regulation and separation device 28 comprising the valve 33 and the oil separator 34.

[0094] 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.

[0095] 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.

[0096] Now, an example of a degassing process for engine 3 implementing the degassing system 4 is described.

[0097] When the engine 3 is running, air from outside the vehicle 1 flows into the air intake 20 and is filtered by the air filter 21.

[0098] 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.

[0099] The compression device 22 and throttle body 23 are controlled by the control system or processing unit 42 to respond in particular to the demand of the driver of the vehicle 1 translated by the depressing of the accelerator pedal, to regulate the mechanical power delivered by the engine 3 propelling the vehicle 1.

[0100] We denote PI the air pressure at the inlet of the compression device 22 generally equal to, or close to, atmospheric pressure i.e. 1 bar, P2 the pressure at the outlet of the compression device 22 and P3 the pressure in the intake manifold 24.

[0101] The compression device 22 compresses the filtered air and delivers the second compressed fluid (compressed filtered air) at its outlet so that the pressure P2 is greater than the pressure PI, the pressure P2 being for example equal to 2 bars.

[0102] As the pressure P2 is greater than the pressure PI, the fourth check 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 vacuum on the suction inlet 36.

[0103] Under the effect of the depression created on the suction inlet 36 by the passage of the second compressed fluid in the Venturi device 35, the first fluid containing gaseous dihydrogen and oil vapors present in the cylinder head 7 is drawn into the device 28.

[0104] The first fluid drawn in by the device 28 creates a vacuum in the bottom of the engine block 6 and in the crankcase, so that the first check valve 27 opens and allows filtered air to enter the crankcase, above the oil tank 8, allowing the volumetric concentration of dihydrogen in the crankcase to be diluted.

[0105] The processing unit 42 controls the valve 33 from the measurements delivered by the sensors 40, 41 so that the difference between the pressure in the crankcase above the oil tank 8 and atmospheric pressure is less than a predetermined negative threshold, for example 50 millibars, and so that the volumetric concentration of dihydrogen in the crankcase is less than a predetermined value, for example 2%.

[0106] Since the difference between the pressure in the crankcase and atmospheric pressure is less than the predetermined negative threshold, the crankcase is under negative pressure relative to atmospheric pressure so that dihydrogen contained in the engine 3 does not escape into the engine compartment 2.

[0107] The predetermined value is chosen so that the volume concentration of dihydrogen is less than the minimum concentration allowing the flammability of dihydrogen, for example 4%.

[0108] The oil separator 34 of the device 28 mechanically separates the oil droplets on the one hand, and on the other hand the oil vapors and gaseous dihydrogen of the first fluid, delivers gaseous dihydrogen on the first outlet 30, and delivers liquid oil resulting from the separation on the second outlet 31.

[0109] When the system 4 includes 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 PI is not sufficient to create a vacuum in the Venturi device 35 to draw the first fluid into the device 28, the vacuum created in the intake manifold 24 by the circulation of the compressed filtered air in the intake ducts 13 allows the third valve 39 to be opened so that the dihydrogen delivered by the device 28 is injected into the intake manifold 24.

[0110] When the system 4 does not include the connection between the outlet 30 of the device 28 and the intake manifold 24, the compression device 22 is sized so that the pressure difference between the pressure P2 and the pressure PI is sufficient to create a vacuum in the Venturi device 35 allowing the first fluid to be drawn into the device 28.

[0111] Unlike the use of a pump dedicated to degassing the crankcase 5 of the engine 3 known from the prior art, the degassing system 4 implements the Venturi device 35.

[0112] The space required for the installation of the Venturi device 35 in the engine compartment 2 is reduced compared to the installation of the pump dedicated to the degassing of the crankcase 5, allowing easier integration of the degassing system 4 into the engine compartment 2.

[0113] Moreover, the Venturi device 35 is more economically advantageous (cheaper) than the pump and does not include moving parts so that the reliability and safety of the degassing system 4 are higher than those of a degassing system including the pump known from the prior art.

Claims

Demands

1. Degassing system (4) for a dihydrogen internal combustion engine (3), the engine (3) comprising a cylinder head (7) and crankcase comprising an oil reservoir (8), characterized in that the degassing system comprises: - an oil regulating 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 regulating and separation device, a high-pressure inlet (37) and an exhaust outlet (38),the Venturi device (35) being configured to draw through the oil regulating 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 regulating and separation device (28) being configured to separate the oil droplets and gaseous dihydrogen from the first fluid, and deliver the gaseous dihydrogen on the first outlet (30) and liquid oil resulting from the separation process on the second outlet (31) so that the oil flows into the oil tank.

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

3. System according to claim 1 or 2, wherein the oil regulating and separating device (28) comprises an oil separator (34) and a regulating 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 control 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 on the other hand the oil vapors and dihydrogen from the first fluid delivered by the control valve, and deliver the dihydrogen on the second connection and the oil on the third connection.

5. System according to claim 3, wherein the oil separator (34) comprises a first connection (45) connected to the inlet (29) of the oil regulating 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 vapors and dihydrogen from the first fluid delivered by the inlet (29) of the oil regulating and separation device (28), and to deliver the dihydrogen on the second connection (30) and the oil on 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 regulating and separation device.

6. System according to any 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 tank (8) and a dihydrogen sensor (41) configured to measure the concentration of gaseous dihydrogen in the crankcase above the oil tank (8), and a processing unit (42) configured to control the regulating valve (33) from the measurements delivered by the pressure sensor and the dihydrogen sensor.

7. A motor vehicle (1) comprising a hydrogen internal combustion engine (3) including a cylinder head (7), an air intake manifold (24) connected to the cylinder head (7) and a crankcase including an oil reservoir (8), the vehicle comprising a compression device (22) including an inlet and an outlet connected to the air intake manifold (24) and configured to compress the second gaseous fluid at the inlet of the compression device (22) and deliver the second compressed gaseous fluid at the outlet of the compression device (22), the vehicle comprising a degassing system (4) according to any one of claims 1 to 6, the inlet (29) of the oil regulating and separation device (28) being connected to the cylinder head (7), the second outlet (31) of the oil regulating and separation device being connected to the cylinder head, the first outlet (30) of the oil regulating 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. A method for degassing a dihydrogen internal combustion engine (3), the engine (3) comprising a cylinder head (7) and a crankcase including an oil reservoir (8), • an inlet (29) and a second outlet (31) of an oil regulating and separation device (28) being connected to the cylinder head (7), • characterized 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 process comprising: - a supply of the high-pressure inlet (37) by a second compressed gaseous fluid such that the second gaseous fluid flows from the high-pressure inlet (37) to the exhaust outlet (38) to draw, through the oil regulation and separation device (38), a first fluid containing gaseous dihydrogen and oil droplets present in the cylinder head (7), - a separation of oil droplets on the one hand, and on the other hand of oil vapors and gaseous dihydrogen from the first fluid in the oil regulation and separation device (28) during the supply of the high-pressure inlet by the second gaseous fluid, - a delivery of gaseous dihydrogen on the first outlet (30), and

9. - a delivery of liquid oil resulting from the separation on the second outlet (31) so that the oil flows into the oil tank (7). Degassing method 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 comprises an actuation of the control valve (33) such that the difference between pressure in the crankcase and atmospheric pressure is less than a predetermined negative threshold and such that the volumetric concentration of dihydrogen in the crankcase is less than a predetermined value.

Images