Description BREATHER ARRANGEMENT FOR THE CRANKCASE OF AN ENGINE [001] The present invention relates to a breather arrangement for the crankcase of an engine as described in the preamble of claim 1, in which arrangement the crankcase and the intake side of the engine combustion air are connected to each other by means of a flow channel for directing crankcase gas to the intake side of the engine and in which a filter device has been arranged in connection with the flow channel.

[002] It is known that as a piston engine runs, blow-by gas is transferred into the crankcase thereof due to various mechanisms. This gas must be purged from the crankcase to avoid an excessive increase in crankcase pressure. Cleaning the crankcase gases and directing them to the intake side of the engine is previously known from publication WO 99/56883. This publication discloses an apparatus for cleaning the gases, in which a rotating rotor impels a rotating motion into the gases, the motion assisting in separating the particles in the gas.

[003] A requirement with the crankcase breathing systems, however, is that the pressure level of the crankcase must not considerably fluctuate. In addition, the amount of gas flowing into the crankcase, i. e. the amount to be removed therefrom, varies according to the running conditions and condition of the engine.

[004] The aim of the present invention is to produce an engine crankcase breather ar- rangement minimizing the problems associated with prior art. An especial aim of the invention is to produce a crankcase breathing arrangement for an engine by means of which the pressure level of the crankcase can be maintained on a certain level regardless of the running conditions of the engine and which, additionally, is reliable and simple.

[005] The aims of the invention are achieved as disclosed in the appended claim 1 and as more closely explained in other claims. In an engine crankcase breather arrangement according to the invention the crankcase is in flow connection with a filter device via a flow channel. The gas in the crankcase can flow away from the crankcase via the filter device, whereby the pressure in the crankcase will not rise to too high a level. The characterizing feature of the invention is that in order to stabilize the pressure of the crankcase the flow channel is continuously connected to the surrounding air space by means of a section between the filter device and the crankcase. This is effected by means of a pressure-equalizing channel. This way, the crankcase is in constant flow connection with the surrounding air. According to the invention, the flow direction in the pressure-equalizing channel is determined according to the pressure conditions and not by means of mechanical closing valves, whereby the pressure level in the crankcase can simply and reliably be kept constant in all conditions. Preferably the pressure level of the crankcase is kept at a level of 0-400 Pa in relation to the surrounding air pressure.

[006] The first section of the flow channel, connecting the filter device with the crankcase of the engine, comprises a first, adjustable flow throttling means, by means of which the pressure losses of the flow channel can be arranged with the pressure equalizing channel so that the pressure level of the crankcase remains on the desired pressure range. In order to connect the pressure-equalizing channel the first section of the flow channel comprises a joint on the section between the first flow throttling means and the filter device. The first section of the flow channel additionally comprises a second adjustable flow throttling means in the section between the joint and the filter device.

[007] According to one embodiment the gases in the crankcase are recycled back into the engine, whereby the second section of the flow channel connects the filter device with the intake side of the engine. The second section of the flow channel in this case ad- ditionally comprises a third adjustable flow throttling means. By means of these, the pressure level of the filter device can be adjusted so as to be as desired in relation to the pressure level on the intake side of the engine. Recycling the gases back into the engine will considerably reduce the total emissions of the engine, because the otherwise harmful compounds of the crankcase gas, such as hydrocarbons, are combusted and thereby are not released into the environment as such.

[008] According to a second embodiment of the invention the crankcase gases can be directed into the environment directly from the filter device. In some applications this can in practice be the most economical method and the arrangement will thereby also be more simple. In this there is no need, for example, for a third adjustable flow throttling means.

[009] In order to maintain a low total pressure loss in the system while still accomplishing a good cleaning of the gas, the filter device comprises means for increasing the pressure of the gas. The said means are preferably provided by arranging the filter device as a centrifugal cleaner. Naturally, a technically similar result can be achieved by means of connecting a different type of filter and, for example, a separate blower in series.

[010] Several advantages are achieved by means of the invention. First, the pressure level of the crankcase stays within desired limits. Further, the arrangement is simple and reliable and it allows even a large volume flow of gas into or out from the crankcase in case of malfunction regardless of the operation or state of the actual filter device.

Using the solution according to the invention the crankcase pressure level adjustment is additionally relatively insensitive to changes of conditions.

[011] In the following the invention is described by way of example and with reference to the appended schematic drawings, of which [012]-figure 1 illustrates a preferable embodiment of an engine crankcase breather ar- rangement according to the invention, and [013]-figure 2 illustrates another preferable embodiment of an engine crankcase breather arrangement according to the invention.

[014] Figure 1 shows a piston engine 1, for example a gas engine. The engine 1 comprises at least one turbocharger 2 utilizing the energy of the exhaust gases in a way known as such for increasing the pressure of the engine combustion air on the intake side 3 of the engine. Engine combustion air is directed via the intake duct 4 of the turbocharger 2 into the compressor 2.1, in which the pressure of the combustion air is increased to a level higher than that of atmospheric pressure. Combustion air is directed to the cylinders 5 of the engine 1, wherein the combustion takes place. The combustion gases are directed via exhaust channel 6 to the turbine 2.2 of the turbocharger, wherefrom they are further directed to, for example, further treatment and release into the en- vironment.

[015] When the motor runs, the blow-by gas flows past its pistons from the combustion chamber of the cylinders 5 into the crankcase 7 of the engine 1, which blow-by gas must be removed from the crankcase to avoid excessive increase of the crankcase pressure. In order to achieve this, the engine comprises a crankcase breather ar- rangement 8, the arrangement having a flow channel 9 by means of which the engine crankcase 7 and the engine intake side 3 are connected to each other. This will produce a system in which all blow-by gas in normal conditions is directed from the crankcase to mix with the combustion air. This allows the total emissions of especially gas engines to be considerably reduced, as the actual combustion products, i. e. exhaust gases, of a gas engine are relatively clean.

[016] The gas flowing from the crankcase usually contains impurities as far as combustion air and the combustion air inlet system are concerned, such as oil mist, and for this reason a filter device 10 has been arranged in connection with the flow channel 9 for cleaning the gas. Because the pressure condition in the crankcase must in all conditions stay relatively constant, in an arrangement according to the invention the flow channel 9 can additionally be connected with the surrounding air space by means of a pressure-equalizing channel 12. In order to achieve this, the flow channel includes a joint 11 to which the pressure equalizer channel 12 is connected.

[017] In the system the first section 9.1 is connected to the crankcase by its one end, the first section being further connected to filter device 10 by its other end. The filter device 10 is connected via the second section 9.2 of the flow channel to the intake side of the engine, to the intake duct 4 of the turbocharger.

[018] In order to set the crankcase pressure conditions suitable for each engine type each application includes a first adjustable throttling device 13.1 and a second adjustable throttling device 13.2 arranged in the first section 9.1 of the flow channel. The in- termediate section of the flow channel is provided with the above-mentioned joint 11.

The section 9.2 of the flow channel between the engine intake side 3 and the filter device 10 further includes a third adjustable flow throttling device 13.3.

[019] In normal conditions the arrangement operates so that blow-by gas flows from the crankcase due to the pressure difference between the pressure on the intake side of the turbocharger and the crankcase pressure. The gas flows via a filter device 10, in which solid and liquid substances are separated from the gas, i. e. mainly oil and other substances formed in the combustion of fuel, such as soot. The separated substances are either redirected back into the engine oil sump via channel 14 or away via channel 15. The cleaned gas is directed to the intake side 3 of the engine and further to the combustion chamber of engine to take part in the combustion of fuel.

[020] The design of the filter device 10 is such as to cause no considerable pressure loss in the system. Because of this, the filter device preferably comprises means 16 for increasing the pressure of the gas. Preferably the means comprise rotatable disc-like pieces supported by a shaft simultaneously acting as centrifugal cleaners and centrifugal blowers/pumps.

[021] The second and third flow throttling means 13.2, 13.3 are used for regulating the pressure level of the filter device 10 to the maximum flow of the gas caused by the engine and the pressure level of the intake side.

[022] As is shown in figure 1 by dotted lines 10.1, 10.2, the joint 11 can be integrated with the actual filter device 10 as well as the first and second flow throttling means 13.1, 13. 2.

[023] Figure 2 illustrates another embodiment, for example in connection with a piston engine 1 running on heavy fuel oil. The reference numbers of figure 2 correspond with those used in figure 1. In this embodiment the gases from the crankcase 7 are directed from the filter apparatus 10 directly to the surrounding air. This means, as a difference to the embodiment of figure 1, that the second section 9.2 of the flow channel is not connected to the intake side 3 of the engine, but it is directed out to the surrounding air.

Thus, there is no need for a third flow throttling means such as shown in figure 1.

[024] Because the pressure conditions must stay relatively constant in all conditions in this embodiment as well, in an arrangement according to the invention first section 9.1 of the flow channel 9 can be connected to the surrounding air space by means of a pressure-equalizing channel 12. In order to achieve this the flow channel also includes a joint 11, to which the pressure-equalizing channel 12 is connected.

[025] In order to set the crankcase pressure conditions suitable for each application, the first section 9.1 of the flow channel is provided with a first adjustable throttling device 13.1 and a second adjustable throttling device 13.2 arranged so that the above- mentioned joint 11 is arranged on the intermediate section of the flow channel. It is essential especially in this embodiment that the construction of the filter device 10 be such as not to cause a considerable pressure loss in the system. Preferably, however, it will even cause an increase of pressure in the gas flowing therethrough. Because of this, the filter device preferably comprises means 16 for increasing the pressure of the gas. In the embodiment shown in the figure the means comprise disclike pieces supported on a rotatable shaft, the pieces acting simultaneously as centrifugal cleaners and centrifugal blowers/pumps while rotating.

[026] In the embodiment shown in figure 2 the arrangement operates so that blow-by gas flows from the crankcase to the surrounding air caused by the total effect of the pressure thereof, the increase of pressure caused by the filter device 10 and the crankcase pressure. The gas flows via a filter device 10, in which solid and liquid substances are separated from the gas, i. e. mainly oil and other substances formed in the combustion of fuel, such as soot. The separated substances are either redirected back into the engine oil sump via channel 14 or away via channel 15. The cleaned gas is directed into the surrounding air via the second section 9.2 of the flow channel.

[027] According to the invention the capacity of filter device 10 is dimensioned so that it can handle a flow slightly exceeding the maximum flow of the engine crankcase gas.

Because of this, in a normal situation under full load, air flows via the pressure- equalizing channel 12 from the environment into the system. Thus, even if the gas flow from the crankcase 7 were very small, the pressure in the crankcase could be maintained at a desired level by setting the first flow throttling means 13.1 into a suitable position so that its pressure loss approximately corresponds with the pressure loss of the pressure-equalizing channel 12 at a certain load.

[028] Using the arrangement according to the invention also allows flows of crankcase 7 gas due to starting or stopping the engine or a larger than normal pressure fluctuation or pressure due to a malfunction without the pressure of the crankcase 7 increasing to too high a level or decreasing to too low a level. This is possible by means of the pressure equalizer channel 12.

[029] The invention is not limited to the embodiments described here, but a number of modifications thereof can be conceived of within the scope of the appended claims. For example, the flow channels are here shown as tubes, but they can be aranged as channels integrated with the engine.