The invention relates to an oil circuit for an engine, in particular a reciprocating piston engine, preferably a marine engine, in particular in an embodiment as a diesel engine, comprising an oil sump and at least one supply loop, which is suppliable with oil from the oil sump, has at least one oil-consuming unit and returns back into the oil sump, and which has a main pump and a plurality of filters, of which at least one is a simple filter with filter area and a further filter is a self-cleaning backwash filter with backwashable filter area, wherein the backwash filter has an inlet, a clean oil outlet and a backwash outlet, and wherein the backwash outlet opens out into a line branch containing at least one means for the treatment of the scavenging oil.

An oil circuit of the generic type is known from DE 196 19 843 C2. In the oil circuit of the generic type, two supply loops are provided, namely one supply loop for lubricating points to be supplied with lubricating oil and a second supply loop for hydraulic power units to be supplied with hydraulic oil. The supply loop leading to the hydraulic power units branches off from the supply loop containing lubricating oil and has an own, self-cleaning filter, wherein the outlet for the fluid generated in the self-cleaning process (oil sludge) opens out into a separating device which is formed by an impulse centrifuge. In turn, a pump is connected directly upstream of the impulse centrifuge in order to achieve an appropriately high rotation speed of the centrifuge, and thus an advantageous separation of solid components and oil. The provision of mutually separated supply loops for lubricating oil and hydraulic oil, wherein an oil is uniformly drawn from the common reservoir (oil sump) and is filtered differently finely for the respective application, has proved its worth, in particular in marine engine

construction.

The object of the invention is to create an oil circuit equipped with filters, in particular for marine engines, which oil circuit is of simple construction, has a low-cost basic concept, and, given an economic operating mode of the employed filters, enables a continuous

improvement of the quality of the oil circulating in the supply loop. To this end, according to a first inventive aspect, it is proposed that the inlet of the backwash filter, in dependence on the switching status of at least one switching valve, can be supplied with oil by the main pump, selectively via a first line section or a second line section, wherein in the second line section is arranged a simple filter. This concept hence intends to enable the inflow to the self-cleaning filter, designed as a backwash filter, via two different line sections, wherein in one line section a simple filter, i.e. a filter which is not self-cleaning, in particular not backwashable, is connected upstream of the backwash filter. In particular in the start-up phase of a marine engine, during the first operating hours or after an overhaul of the marine engine, this line section is connected upstream of the inflow or inlet of the backwash filter in order in this operating time to extract a large part of the impurities in the oil definitively from all line branches, and thus also from the oil sump. Only after a sufficiently lengthy start-up phase is a switch then made to the other line section, wherein this then enables the simple filter, which is anyway present, to now be used for another application, as is further explained with reference to the sub-claims.

According to an, in particular, preferred embodiment, the line branch for the scavenging oil can be assigned a scavenging oil pump and, downstream of the scavenging oil pump, a simple filter, the filter exit of which, preferably with the interposition of a shut-off member, opens out into the inlet of the backwash filter. This simple filter is here preferably constituted by precisely that simple filter which, during the start-up phase described further above, is located in the inflow of the backwash filter. Through the provision of a pump in the line branch for the scavenging oil, even during this start-up phase the backwash fluid can in this case be fed out of the backwash filter into the line section provided with the simple filter. Despite the use of a backwash filter, the entire volumetric flow in the supply loop behind the backwash filter is hence then available for the units, in particular hydraulic power units, to be supplied, whereby it is at the same time enabled that the main pump, with which the oil is drawn from the oil sump, can be equipped with or operated with lower power. In particular for

maintenance purposes with respect to the scavenging oil pump, it is advantageous if, in the line branch for the scavenging oil, a shut-off member is arranged between the scavenging oil pump and the filter entrance. Alternatively or additionally, a pressure indicator can also be arranged, in order to be able to check the degree of contamination of the simple filter.

In an alternative embodiment of an oil circuit, in the line branch for the scavenging oil a scavenging oil pump, and downstream of the scavenging oil pump, for the scavenging oil treatment, a centrifuge, in particular an impulse centrifuge, can be arranged, wherein downstream of the centrifuge is/are arranged a collecting tank and/or a return line into the oil sump. According to one design variant, the collecting tank can be connected to the inlet of the backwash filter via a feed line and a pump disposed in the feed line.

While surrendering some of the aforementioned advantages, the line branch for the scavenging oil could also be assigned a scavenging oil pump and, downstream of the scavenging oil pump, a simple filter, the filter exit of which then preferably opens out directly into the oil sump.

In an alternative embodiment, in dependence on the switching status of the switching valve arranged upstream of the backwash filter and in combination with the switching status of a switching member disposed in the line branch for the scavenging oil, oil can selectively be fed by the main pump, or scavenging oil from the line branch for the scavenging oil, to the filter entrance of the simple filter. In this oil circuit, no scavenging oil pump is hence then provided in the line branch for the scavenging oil, so that the volumetric flow of the scavenging oil is not available to supply the units connected downstream of the backwash filter. But in this case too, it proves advantageous that the simple filter which is anyway present, in any event after completion of the start-up phase, i.e. during normal operation of the engine, in which the switching valve arranged upstream of the backwash filter shuts off the line section to the simple filter and switches over to the other line section, can be used for after-cleaning of the scavenging oil and, in this respect, continuously improves the quality of the oil circulating between oil sump and consuming units. In particular, in this embodiment it is then preferred that the filter outlet of the simple filter in normal operation, when the switching valve arranged upstream of the backwash filter shuts off the line section to the simple filter, is connected up to a return line to the oil sump. Here too, the return line can then preferably be assigned a shut-off member in order to, if need be, exchange a filter insert in the simple filter, for instance, including in running operation.

According to a second inventive concept, an oil circuit in which the line branch for the scavenging oil is assigned a scavenging oil pump and, downstream of the scavenging oil pump, a simple filter, the filter exit of which opens out into the inlet of the backwash filter, is proposed. As already described further above, this measure can achieve the effect that the whole of the volumetric flow of oil which is delivered by the main pump is available to all consuming units connected downstream of the backwash filter, whereby the main pump can be given a lower pumping capacity, and, at the same time, furthermore, the quality of the oil circulating in the supply loops is permanently improved.

Here too, it is particularly advantageous, in particular when such an oil circuit is used in respect of a marine engine, in particular a large diesel engine, if the inlet of the backwash filter, in dependence on the switching status of at least one switching valve, can be supplied with oil by the main pump, selectively via a first line section or a second line section, wherein in the second line section is arranged a simple filter. In particular for maintenance purposes, in the line branch for the scavenging oil a shut-off member and/or a pressure indicator can be arranged between the scavenging oil pump and the filter entrance.

In all embodiments of the oil circuit, it is advantageous if the filter area of the simple filter or filters is larger than the backwashable filter area of the backwash filter, and preferably is at least 5 times larger than the filter area of the backwash filter and/or maximally 15 times larger than the backwashable filter area of the backwash filter. Even if the simple filter then after the start-up phase has a certain degree of contamination, it can then, without replacement, continue to be used for numerous further operating hours for the scavenging oil treatment and, if used purely in the scavenging oil treatment, extremely long maintenance-free service lives are enabled. It is further advantageous if the filter fineness of the filter area of the simple filter is finer than the filter fineness of the filter area of the backwash filter, wherein preferably the filter fineness of the simple filter is finer by a factor of 2 to 5 than the filter fineness of the backwash filter.

As is customary per se, in the oil circuit between the main pump and the switching valve arranged upstream of the backwash filter can be arranged at least one rough filter, the filter fineness of which is coarser than the filter fineness of the filter areas of the simple filter and of the backwash filter.

In the preferred field of application of the oil circuit according to the invention, the engine is constituted by a marine engine, and the backwash filter there serves for the treatment of the oil from the oil sump as hydraulic oil, in which case, correspondingly, in the supply loop comprising the backwash filter, there is or are arranged, as oil-consuming units, at least one hydraulic power unit, and preferably a plurality of hydraulic oil power units. In particular in an oil circuit for a marine engine, it is particularly advantageous if the backwash filter, irrespective of the switching status of all switching valves and switching members, both in normal operation and in a start-up operation in the first operating hours of a new or reconditioned engine, is connected upstream of all oil-consuming units, in particular hydraulic power units, in the supply loop for the fine filtering of the oil. In such oil circuits, there can further be provided, as is known per se, at least a second supply loop, in which there are arranged as oil-consuming units one, or preferably a plurality of lubricating points to be lubricated with oil, wherein preferably the second supply loop behind the main pump, in particular behind a rough filter connected downstream of the main pump, branches off from the first supply loop comprising the backwash filter.

Further advantages and embodiments of the invention emerge from the sub-claims and from the following description of schematic illustrative embodiments, shown schematically in the drawing with their main component parts, for oil circuits according to the invention for marine engines. In the drawing:

FIG 1 shows a flow chart of an oil circuit for a marine engine with pump in the

scavenging oil line branch during a start-up phase of the engine;

FIG 2 shows the flow chart from Figure 1 during normal operation of the engine;

FIG 3 shows a flow chart of an oil circuit for a marine engine without pump in the scavenging oil line branch during a start-up phase of the engine;

FIG 4 shows the flow chart from Figure 3 during normal operation of the engine;

FIG 5 shows a flow chart of an oil circuit for a marine engine with centrifug

scavenging oil line branch during a start-up phase of the engine;

FIG 6 shows the flow chart from Figure 5 during normal operation of the engine;

FIG 7 shows a flow chart of an oil circuit for a marine engine with pump and simple filter in the scavenging oil line branch during a start-up phase of the engine; and FIG 8 shows the flow chart from Figure 7 during normal operation of the engine.

In FIG 1 and 2, an oil circuit 10 according to a first illustrative embodiment for a marine engine 1 (indicated only symbolically) with oil pan as the oil sump 2 is represented with the aid of a flow chart. By means of the oil circuit 10, both hydraulic power units and lubricating points on the or for the marine engine 1 are supplied with oil, wherein, for this purpose, mutually separated supply loops 20, 40 are provided. To this end, the flow chart shows, on the one hand, a supply loop 20 for hydraulic power units (not represented in detail) on the marine engine 1 and, in addition, a second supply loop 40 for lubricating points (also not

represented). The supply loop 40 for the lubricating points (not represented) on the marine engine 1, such as, for instance, the bearings of crankshaft, connecting rod, camshaft, rockers or valves, is representatively referred to within the Application as the second supply loop 40, whereas the supply loop 20 for the hydraulic power units is representatively referred to as the first supply loop. Naturally, further supply loops or line sections could be provided both for the lubricating points and for the hydraulic power units.

In the shown diagram of the flow chart for the oil circuit 10, both the first supply loop 20 and the second supply loop 40 are supplied with oil from the same oil pan, hereinafter solely referred to as the oil sump 2, which oil, for this purpose, is drawn from the oil sump 2 by means of a main pump 3 and subjected to a predefined pressure. In the shown flow chart, between the engine 1 and the main pump 3 is found a line 5. The main pump can also, however, be integrated in the engine. Behind the main pump 3 is arranged a first filter 4, which normally forms the main lubricating oil filter and by which contaminations are filtered out of the oil emanating from the oil sump 2, so that all lubricating oil-consuming units can be lubricated with the oil filtered by means of the filter 4. In the shown flow chart, behind the filter 4, in a line formed by a tube and/or hose, is found a branch-off point 6, from which the supply loop 40 for the lubricating points or lubricating oil consuming units to be lubricated with lubricating oil, and the supply loop 20 for the hydraulic power units to be supplied with hydraulic oil, run in separated arrangement. The lubricating oil and the hydraulic oil are in this case provided by means of the same oil from the oil sump 2, wherein, in the second supply loop 40 for the lubricating oil, normally no further treatment of the oil takes place, so that this supply loop 40 is represented in the flow chart solely by a dotted line going back to the marine engine 1. The invention relates substantially only to the embodiment of the supply loop 20 for supplying hydraulic power units with hydraulic oil. The treatment of the oil from the oil sump 2 is in this case realized primarily by means of a self-cleaning automatic filter, referred to generally within the Application as the backwash filter 11. Corresponding automatic filters or backwash filters are known in the prior art. A fluid, here the oil to be filtered, passes via an inlet 12 into a housing, in the filtering operation of a backwash filter 11 through its filter area 13, so as then to be fed, as filtrate or clean oil filtered in accordance with the specific requirements of the engine manufacturer, via the clean oil outlet (filtrate outlet) 14 to the hydraulic power units on the marine engine 1. In the application which is described here, the filtrate/clean oil hence forms the hydraulic oil for the hydraulic power units connected downstream of the backwash filter 11. The backwash filter 11 can be constituted, for instance, by a candle filter having a plurality of backwashable filter candles, as is described, for instance, in EP 0 900 584 Al or EP 0 656 223 Al . In the backwashing process, individual filter candles are then connected on one side or both sides via backwash members to a backwash outlet 15 on the backwash filter 11, in order to clean off the filter area 13 in counterflow to the filtering direction, and preferably also in crossflow. The backwash medium is in this case mostly the clean oil, which therefore behind the backwash filter 11 is no longer available for the units connected downstream of this and reduces the volumetric flow of filtrate/clean oil. Via the backwash outlet 15, the impurities dissolved in the backwashing process on the filter area, together with the backwash medium, here therefore the clean oil, are in turn led out of the backwash filter 11. The degree of contamination of the entire filter area can be read off, for instance, with the aid of a manometer as the pressure indicator 16 and the pressure difference between the filter inlet 12 and the clean oil outlet 14. The basic structure of a backwash filter of this kind is known to the person skilled in the art, so that no detailed description of the structure and of the working method of the backwash filter is given here.

An aspect which is fundamental to the oil circuit according to the invention lies in the fact that here the backwash filter 11 in the supply loop 20 is in all operating modes and at all times connected upstream of the hydraulic power units and has therefore to ensure that the hydraulic oil fed to the hydraulic power units has that degree of purity which is defined by the specifications of these power units or of the engine manufacturer. In the preferred inventive embodiment of the oil circuit 10, a bypass for the backwash filter 11 is not provided. In the supply loop 20 of the oil circuit 10 according to the invention, the inlet 12 of the backwash filter 11 can be supplied, via two separate line sections 21, 22, with the oil flow pressurized and delivered by the main pump 3, wherein the selection of the active line section 21 or 22 is made via a switching valve 23, connected upstream of the said line section, in the supply loop 20. The switching valve 23 is preferably constituted by a multi-way valve with suitable switching member.

In the switch position in the flow chart according to FIG 1, the switching valve 23 shuts off the line section 22, which is therefore represented as a dashed line, and the oil supply to the backwash filter 15 is realized via the line section 21. The flow chart according to FIG 1 is in this case preferably employed in a start-up phase of a marine engine 1, thus, for instance, during the first 200 operating hours of a new or reconditioned marine engine 1. In this operating time, there is still an elevated impurities component in the oil, for example stemming from the manufacture, assembly, start-up or maintenance of the individual units of the marine engine 1, wherein in particular these operating hours can be responsible for the durability of the marine engine 1 as a whole. In order to eliminate this problem in the start-up phase, in which an elevated impurities component can be present, in the line section 21 is installed a filter which is non-backwashable and is therefore referred to as a simple filter 25 and the filter area 26 of which has a filter fineness which is preferably finer, by several factors, than the filter fineness of the filter area 13 of the backwash filter 11. The filter area 26 of the simple filter 25 is at the same time preferably 5 times to 15 times, preferably 6 times to 12 times larger, than the filter area 13 of the backwash filter 11, in order to obtain a long operating time of the simple filter 25 despite the absence of self-cleaning.

In the oil circuit 10 according to the invention, the simple filter 25 with its filter area 26 has at the same time the function of filtering the backwash fluid or scavenging oil which exits from the backwash outlet 15 on the backwash filter 11. To this end, starting from the backwash outlet 15, a line branch 24 for the scavenging oil is provided, which line branch opens out into a filter entrance 27 on the simple filter 25. In the illustrative embodiment of the oil circuit 10 in accordance with FIG 1 and 2, in the line branch 24 for the scavenging oil is arranged a scavenging oil pump 28, which subjects the scavenging oil to an appropriate pressure in order that it can flow via the filter inlet 27, including in the position of the switching valve 23 according to FIG 1, i.e. shut-off of the line section 22, together with the oil flowing in from the main pump 3, into the simple filter 25. One advantage to be gained is in this case that the volumetric flow delivered by the main pump 3 into the supply loop 20 remains fully available to the hydraulic power units. The second advantage is that the impurities in the scavenging oil do not make their way back into the oil circuit, in particular into the oil sump 2, so that the after-treatment of the scavenging oil with the filter area of the simple filter 25 continuously ensures an improvement of the oil quality of the oil which overall is present and circulates in the whole of the oil circuit 10. In the flow chart, the oil emanating from the main pump 3 passes via the switching valve 23 and the line connecting hereto, into the simple filter 25 via a filter entrance 27A, whilst the oil from the line branch 24 passes via a filter entrance 27 into the simple filter 25. The two filter entrances 27, 27A could also be formed by an individual entrance, through the merger, for instance, of the respective lines. The oil flow formed by the two partial volumetric flows then passes through the filter medium 26 of the simple filter, out of the simple filter 25 at the filter outlet 33, and into the inlet 12 of the backwash filter 11, so as there to be available again.

In the shown illustrative embodiment in FIG 1 and FIG 2, in the line branch 24 for the scavenging oil, in front of and behind the pump 28, are respectively arranged a shut-off member 29 and a shut-off member 30, which could consist of a simple switch tap, in order to be able, if need be, to perform repairs on the pump 28. Downstream of the shut-off member 30 disposed behind the pump 28, a manometer is further installed as a pressure indicator 31 in the line branch 24, in order to be able to draw from the pressure indicator 31 conclusions regarding the degree of contamination of the simple filter 25. According to one further modification, the line branch 24 for the scavenging oil could be provided, as shown in Fig. 1 and 2 in dotted lines, with a 3 -way valve 49 instead of a simple shut-off member 29, as well as with a return branch 44 connecting the additional outlet of the 3 -way valve 49 to the oil sump 2. This preferred modification avoids an unintended shut-off of the line branch 24 for the scavenging oil and enables to return the scavenging oil into the oil sump 2 if problems e.g. with the pump 28 should occur.

The flow chart in FIG 2 differs from that according to FIG 1 solely on the basis of the switch position of the switching valve 23 assigned to the separate line sections 21, 22. The flow chart in FIG 2 corresponds to the normal operation of the oil circuit 10 of a marine engine 1. In the flow chart according to FIG 2, the second line section 21 is shut off and oil passes from the main pump 3, directly via the first line section 22, into the inlet 12 of the backwash filter 11. The inactive line 37, located between the switching valve 23 and the simple filter 25, of the line section 21 is in FIG 2 therefore shown correspondingly in dashed representation, whereas the line in the line section 22, as an active line, is represented with a continuous line. Despite the altered switch position of the switching valve 23, the simple filter 25 additionally fulfils the object of treating the scavenging oil in the line branch 24 and filtering out its impurities entrained in the backwashing. As described with reference to FIG 1, the appropriately treated, filtered scavenging oil is fed to the inlet 12 of the backwash filter 11 parallel to the oil emanating directly from the main pump 3. Primarily for maintenance purposes, in the oil circuit 10, into the line between the filter outlet 33 of the simple filter 25 and the inlet 12 of the backwash filter 11 in the line section 21, is provided a further, preferably simple shut-off member 32, such as, for instance, a valve flap, or preferably a non-return valve, which works automatically and avoids wrong switching .

In FIG 3 and FIG 4, a slightly modified oil circuit 110 is represented in corresponding flow charts. The arrangement of the switching valve 23 connected upstream of the backwash filter 11, the structure of the backwash filter 11 with inlet 12, filter area 13, clean oil outlet 14, backwash outlet 15 and pressure indicator 16, as well as the activation of the backwash filter 11 via two separate line sections 21, 22 with a simple filter 125 in the second line section 21 in the case of the supply loop 120, is exactly the same as in the previous illustrative embodiment, so that the same reference symbols are used for these elements in the oil circuit 110 and reference is made to the above description. However, the line branch 124 for the scavenging oil is configured other than in the previous illustrative embodiment, since no pump is provided in the line branch 124. The line branch 124 therefore here has only one shut-off member 129, as well as a pressure indicator 131, but, as in the previous illustrative embodiment, opens out into a filter inlet 127 on the simple filter 125. This leads to a slightly different usage and function of the simple filter 125 both in the start-up phase, as represented with the flow chart in FIG 3, and in normal operation in accordance with the representation of the flow chart in FIG 4. In the start-up phase, when the switching valve 23 shuts off the line section 22, although the oil flows, as in the previous illustrative embodiment, firstly on the basis of the corresponding switch position of the switching valve 23, which switch position produces an active line section 21, via the line 137 to the simple filter 125 and is there filtered by means of the filter area 126 thereof before making its way to the inlet 12 of the backwash filter 11, in this operating phase, in the shown illustrative embodiment, the entire line branch 124 for the scavenging oil is shut off by means of the shut-off member 129, and hence, in the flow chart according to FIG 3, no backwash takes place in the start-up phase. The lines in the line branch 124 are therefore represented correspondingly in dashed lines. A backwash could then take place if, according to an alternative embodiment (not represented), the shut-off member in the line branch for the scavenging oil is realized, for instance, as a multi-way valve, and in the start-up phase the scavenging oil is fed via a further line section to a further filter or a separating device, before it is fed back into the oil pan, or else flows back unfiltered into the oil sump 2.

In the normal operation of the oil circuit 110 on the other hand, as represented in FIG 4, a backwash takes place and the shut-off member 129 is open. The switching valve 23 connected upstream of the backwash filter 11 shuts off the line section 21 and feeds the oil emanating from the main pump, via the line section 22, directly to the inlet 12 of the backwash filter. The scavenging oil generated in the backwash passes via the line in the line branch 124 at the filter inlet 127 into the simple filter 125 and is cleaned by means of its filter area 126, before it runs back via a return line 135, which can preferably be shut off by means of a shut-off member 136, in particular for the start-up phase according to FIG 3, appropriately cleaned of the impurities, into the oil sump 2. The return line 135 is hence active only in normal operation of the oil circuit 110, and therefore represented in FIG 4 with a continuous line and represented in FIG 3 as an inactive line with dashed line. The line branch 124 for the scavenging oil could be provided, as shown in Fig. 3 and 4 in dotted lines, with a 3 -way valve 149 instead of a simple shut-off member 129 as well as a connecting branch 145 to return line 135, connecting the additional outlet of the 3-way valve 149 to the oil sump 2. This preferred modification avoids an unintended shut-off of the line for the scavenging oil and enables to return the scavenging oil into the oil sump 2 if problems should occur.

In FIG 5 and FIG 6, a once again modified oil circuit 210 is represented in corresponding flow charts. The arrangement of the switching valve 23 connected upstream of the backwash filter 11, the structure of the backwash filter 11 with inlet 12, filter area 13, clean oil outlet 14, backwash outlet 15 and pressure indicator 16, as well as the activation of the backwash filter 11 via two separate line sections 21, 22 with a simple filter 225 in the line section 21 in the case of the supply loop 220, is exactly the same as in the two previous illustrative

embodiments, so that the same reference symbols are in turn used for these elements in the oil circuit 210 and reference is made to the above description. However, the line branch 224 for the scavenging oil is once again configured other than in the two previous illustrative embodiments, since, although in the line branch 224 a pump 228 is provided behind the backwash outlet 15 on the backwash filter 11, this pump 228, in the case of the oil circuit 210, is connected upstream of a centrifuge 251, in particular an impulse centrifuge, by means of which the scavenging oil in the associated line branch 224 is treated. The line branch 224 here has no shut-off member, but rather the centrifuge exit or exits of the centrifuge 251 lead to a collecting tank 253 arranged downstream of the centrifuge 251, such as, for instance, a catch pan with collecting tank. The volumetric flow of treated scavenging oil, which volumetric flow can once again be fed to the backwash filter 1 1 by means of a supply line 254 and a further pump 255, both during the start-up phase shown in FIG 5 and in normal operation according to FIG 6, when the switching valve 23 correspondingly switches over to the line section 22, or it is fed, according to an alternative design variant indicated in FIG 6 with the dash-dotted return line 261, directly to the oil sump 2 of the engine 1. In this variant, the collecting tank, if need be, could even be omitted. Through the provision of a further switching valve, both variants shown in Fig. 6 could also be realized simultaneously. And shut-off members , either e.g. switchable flap valves or non-return valves, could be provided in all or individual lines, in particular for maintenance purposes.

FIG 7 and FIG 8 show the associated flow charts relating to a fourth design variant for an oil circuit 310. The arrangement of the switching valve 23 connected upstream of the backwash filter 11, the structure of the backwash filter 11 with inlet 12, filter area 13, clean oil outlet 14, backwash outlet 15 and pressure indicator 16, as well as the activation of the backwash filter 11 via two separate line sections 21 and 22, wherein a simple filter 325 is arranged in the line section 21, is once again exactly the same as in the previous illustrative embodiments, so that reference is here too made to the above description. In the line branch 324 for the scavenging oil exiting from the backwash filter 11 at the backwash outlet 15 are arranged a pump 328 and a simple filter 377, connected downstream of the pump 328, which filter is having a filter exit 378. The scavenging oil treated with the separate, additional simple filter 377 is either, as indicated in the illustrative embodiment of FIG 7 for the start-up phase, in which the backwash filter 11 is fed via the line section 21 through the simple filter 325 provided in line section 21, by means of a supply line 354 connected up to the filter exit 378, once again fed to the entrance of the backwash filter 11, or, as indicated with the dash-dotted line 376 in FIG 8, it is fed directly to the oil sump 2 of the engine 1. Here too, through the provision of a further switching valve, both design variants could be realized simultaneously in one oil circuit, and shut-off members could be provided in all or individual lines, in particular for maintenance purposes. The different filter finenesses in the simple filter and in the backwash filter could, already be achieved for instance, by virtue of the fact that the filter area in the simple filter consists of a non-woven fabric, in particular a cellulose, synthetic or glass fibre non-woven fabric, whereas the filter area in the backwash filter consists of a woven fabric, such as a metal or synthetic fabric. The filter area in the backwash filter could also consist of a sintered non-woven fabric or an edge filter design. The filter area of the simple filter is preferably exchangeable. A considerably larger filter area of the simple filter relative to that of the backwash filter can achieve the effect that, despite the finer filtration in the simple filter, a long, maintenance-free service life is ensured.

For the person skilled in the art, numerous modifications which should fall within the scope of the appended claims emerge from the preceding description. The flow charts show only the basic structure, and further line branches or supply loops could be provided. In particular, the presence and/or the structure of a lubricating oil circuit are not vital to the invention. There can also be provided further lubricating oil circuits, which are not even connected up to the main lubricating oil filter. Oil circuits according to the invention could also be used in other engines, even though marine engines, in particular large diesel engines, pertain to the preferred field of application of the present invention. The arrangement of a pump in the line branch for the scavenging oil and the treatment of the scavenging oil with a filter, which scavenging oil is set with the pump to an elevated pressure, can also offer advantages when the scavenging oil is not fed to the automatic filter or backwash filter, but to other consuming units. Such and other modifications are intended to fall within the scope of the appended claims.