OIL SUMP, AN INTERNAL COMBUSTION ENGINE, A VEHICLE AND A METHOD

Abstract

An oil sump, an internal combustion engine, a vehicle and a method are disclosed. The oil sump comprises a container defining a volume for containing oil in which the volume comprises a primary volume for containing an oil outlet, a secondary volume and an intermediate volume. A first wall divides the primary volume from the intermediate volume. The first wall comprises a first restricted flow means configured to enable a restricted flow of oil from the intermediate volume to the primary volume. A second wall comprising a second restricted flow means is arranged to divide the secondary volume from the intermediate volume. A top-up arrangement is configured to direct returned oil to the secondary volume and enable excess returned oil to overflow into the intermediate volume. A first weir means is positioned to enable an overflow of returned oil into the primary volume.

Claims

1. An oil sump comprising: a container defining a volume for containing oil, the volume comprising a primary volume, a secondary volume and an intermediate volume; a first wall dividing the primary volume from the intermediate volume, the first wall comprising a first restricted flow means configured to enable a restricted flow of oil from the intermediate volume to the primary volume; a second wall dividing the secondary volume from the intermediate volume comprising a second restricted flow means configured to enable a restricted flow of oil from the secondary volume to the intermediate volume; a first weir means positioned to enable a first overflow of oil into the primary volume; a top-up arrangement configured to direct returned oil to the secondary volume and enable excess returned oil to overflow into the intermediate volume; and an oil outlet for pumping oil from the primary volume to an internal combustion engine.

2. The oil sump of claim 1, wherein the first weir means comprises a first weir wall for allowing the first overflow of oil to flow from the intermediate volume over the first weir wall into the primary volume.

3. The oil sump of claim 1, wherein the first weir means is configured to enable the first overflow of oil when oil within the intermediate volume is above a first height; the top-up arrangement is configured to enable the excess returned oil to overflow into the intermediate volume when oil within the secondary volume is above a second height; and the second height of oil is equal to or higher than the first height of oil.

4. The oil sump of claim 1, wherein the first restricted flow means comprises a trap door configured to move from a closed position to an open position at, or above, a threshold temperature.

5. The oil sump of claim 1, wherein one or both of the first restricted flow means and the second restricted flow means comprises a mesh.

6. The oil sump of claim 1, wherein the second restricted flow means comprises: a trap door configured to move from a closed position to an open position at, or above, a threshold temperature.

7. The oil sump of claim 1, further including a cover extending over a first portion of the intermediate volume and positioned to enable the excess returned oil from the top-up arrangement to fall onto the cover; wherein the cover defines at least one hole to enable oil to enter the first portion of the intermediate volume.

8. The oil sump of claim 7, wherein the at least one hole of the cover is dimensioned to provide a first resistance to flow of oil at an operational temperature; the first restricted flow means of the first wall is dimensioned to provide a second resistance to flow of oil at the operational temperature; and the second resistance is lower than the first resistance.

9. The oil sump of claim 1, wherein the secondary volume contains a deflection means configured to deflect returned oil entering the secondary volume away from the second restricted flow means of the second wall.

10. The oil sump of claim 1, wherein the first wall surrounds the primary volume and the second wall surrounds the intermediate volume and the first wall.

11. The oil sump of claim 1, wherein: the container comprises an outer wall and a plurality of baffles configured to direct flow of oil within the container, the plurality of baffles defining a pickup chamber for containing an oil outlet and a plurality of outer chambers surrounding the pickup chamber.

12. The oil sump of claim 11, wherein at least a portion of each one of the plurality of baffles extends from a respective first position adjacent to the outer wall to a respective second position adjacent to the pickup chamber.

13. The oil sump of claim 12, wherein the plurality of baffles extend from the respective second positions around the pickup chamber in the same rotational direction.

14. The oil sump of claim 1, wherein the top-up arrangement comprises: a second weir means positioned to enable the excess returned oil to overflow from the top-up arrangement into the intermediate volume; and a first cover wall positioned to cover the secondary volume, the first cover wall having an outer surface configured to enable oil falling on the outer surface to flow towards the intermediate volume via the second weir means.

15. The oil sump of claim 14, wherein the first cover wall defines at least one opening to enable oil to flow from the outer surface into the secondary volume.

16. The oil sump of claim 14, wherein the second weir means comprises a second weir wall for allowing the excess returned oil to flow over the second weir wall into the intermediate volume.

17. The oil sump of claim 14, wherein the oil sump comprises a second cover wall positioned over the primary volume, the second cover wall being arranged to direct oil falling on the second cover wall onto the first cover wall.

18. The oil sump of claim 14, wherein the first cover wall comprises a trough, and an opening extends through a tube extending from the trough.

19. A vehicle comprising the oil sump of claim 1.

20. A method of circulating oil through a sump of an internal combustion engine, the sump comprising a first wall dividing a primary volume from an intermediate volume and a second wall dividing a secondary volume from the intermediate volume, the method comprising: pumping oil from the primary volume of the sump; allowing oil returned from the internal combustion engine to flow into the secondary volume of the sump; in dependence on the secondary volume being full, allowing returned oil to overflow into the intermediate volume of the sump to fill the intermediate volume; allowing oil to overflow into the primary volume wherein a first rate of oil leakage through the first wall depends on a temperature of oil neighboring the first wall and a second rate of oil leakage through the second wall depends on a difference in fluid pressure across the second wall; and at temperatures of the oil neighboring the first wall that are below a threshold temperature, allowing oil to flow into the intermediate volume at a rate that maintains a volume of oil in the intermediate volume sufficient to resist leakage of oil through the second wall.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0048] FIG. 1 shows a vehicle comprising an internal combustion engine that has an oil sump embodying the present invention;

[0049] FIG. 2 shows a plan view of the oil sump;

[0050] FIG. 3 shows a cross-sectional view of the sump;

[0051] FIG. 4 shows an equal level of oil in each of three volumes of the sump;

[0052] FIG. 5 shows the sump shortly after starting the engine, when secondary volume and an intermediate volume have filled with oil;

[0053] FIG. 6 shows the sump when oil in the intermediate volume has warmed up and the levels of oil in the intermediate volume and secondary volume have started to fall;

[0054] FIG. 7 shows a perspective view of an alternative oil sump that embodies the present invention;

[0055] FIG. 8 shows a cross-sectional view of the alternative oil sump of FIG. 7;

[0056] FIG. 9 shows the sump of FIG. 8 with a trap door in a closed position and the same level of oil in each of the three volumes;

[0057] FIG. 10 shows the oil sump of FIG. 8 with the secondary volume and the intermediate volume full of oil and excess oil flowing over a second weir wall and a first weir wall into a primary volume;

[0058] FIG. 11 shows the sump of FIG. 8 with a trap door open, the level in the intermediate volume reduced approximately the same as that in the primary volume and all returned oil flowing into the secondary volume;

[0059] FIG. 12 shows the sump of FIG. 8 when the engine has been turned off and oil in the three volumes is able to equalize;

[0060] FIG. 13 shows another alternative sump embodying the present invention;

[0061] FIG. 14 shows an embodiment of the engine of FIG. 1 comprising an alternative oil sump 103A;

[0062] FIG. 15 shows a plan view of the sump of FIG. 14 with an upper sump wall in place;

[0063] FIG. 16 shows a plan view of the sump of FIG. 14 with the upper sump wall removed;

[0064] FIGS. 17 and 18 show flows, at different times, around the baffles in the vicinity of a pickup chamber of the sump of FIG. 14;

[0065] FIG. 19 shows a cross-sectional view of the sump of FIG. 14;

[0066] FIG. 20 shows the same level of oil in each of three volumes within the sump of FIG. 14;

[0067] FIG. 21 shows the sump of FIG. 14 shortly after starting the engine, when a secondary volume and an intermediate volume are filled with oil;

[0068] FIG. 22 shows the oil sump when the level of oil in the intermediate volume has dropped and the level of oil in the secondary volume has begun to drop; and

[0069] FIG. 23 shows a plan view of another alternative sump embodying the present invention.

DETAILED DESCRIPTION

[0070] A vehicle 101 is shown in FIG. 1. The vehicle 101 comprises an internal combustion engine 102, which has an oil sump 103. The internal combustion engine 102 (referred to below simply as the engine 102) may have a construction that is generally known in the art, except for the oil sump 103, which will be described in detail below.

[0071] In the present embodiment the vehicle 101 is a car, but in alternative embodiments, the vehicle 101 may be another type of road vehicle or a vehicle other than a road vehicle that comprises an internal combustion engine.

[0072] FIG. 2 shows a plan view of the oil sump 103, and FIG. 3 shows a cross-sectional view of the sump 103 through the plane 201 shown in FIG. 2. The oil sump 103 comprises a container 202 having a lower wall 203 and an outer wall 204 extending upwards from the lower wall 203. The lower wall 203 and the outer wall 204 of the container 202 define a volume 205 for containing oil (not shown in FIGS. 2 and 3). The volume 205 comprises three volumes: a primary volume 206; a secondary volume 207; and an intermediate volume 208. The primary volume 206 is suitable for containing an oil outlet 209 on a pickup tube 210, or an oil pump, to enable oil to be pumped from the sump 103 during use.

[0073] A first wall 211 divides the primary volume 206 from the intermediate volume 208, and a second wall 212 divides the secondary volume 207 from the intermediate volume 208. A portion 213 of the first wall 211 may be impervious to oil, but the first wall 211 comprises a first restricted flow means 214 configured to enable a restricted flow of oil from the intermediate volume 208 to the primary volume 206. The first restricted flow means 214 is configured to provide a passageway for a flow of oil from the intermediate volume 208 to the primary volume 206 when oil adjacent to the first restricted flow means 214 is above a first threshold temperature. The first restricted flow means 214 may be configured to allow a slower flow of oil for temperatures below the first threshold temperature.

[0074] Similarly a portion 215 of the second wall 212 may be impervious to oil, but the second wall 212 comprises a second restricted flow means 216 configured to enable a restricted flow of oil from the secondary volume 207 to the intermediate volume 208. The second restricted flow means 216 is configured to provide a passageway for a flow of oil from the secondary volume 207 to the intermediate volume 208 when oil adjacent to the second restricted flow means 216 is above a second threshold temperature. The second restricted flow means 216 may be configured to allow a slower flow of oil for temperatures below the second threshold temperature. The second threshold temperature may be equal to the first threshold temperature.

[0075] In the present embodiment, the first restricted flow means 214 and second restricted flow means 216 each comprise a mesh 214A and 216A respectively. Consequently, motor oil is able to leak through the first and second restricted flow means 214 and 216 when the oil is hot and has relatively low viscosity and also when it is cold and has relatively high viscosity. However, it will be understood that the hot oil is able to flow more easily through the mesh 214A and 216A when the oil is hot.

[0076] In the present embodiment, the holes in the mesh 214A and 216A have dimensions of about 0.2 mm but in alternative embodiments the holes may have dimensions of between 0.1 mm and 0.5 mm.

[0077] In alternative embodiments, the first and/or second restricted flow means 214 and 216 may each comprise an opening in the respective wall 211 and 212 and a trap door actuated by a bimetallic strip configured to maintain the trap door in a closed position for temperatures below a threshold temperature and to open the trap door above the threshold temperature. The trap doors may allow a relatively small flow of oil to leak through the respective opening when they are in the closed positions. (An embodiment that includes a trap door will be described later below with regard to FIGS. 7 to 12.)

[0078] The oil sump 103 also comprises a first weir means 217 that is positioned to enable a first overflow of oil from the intermediate volume 208 into the primary volume 206 when oil within the intermediate volume 208 is above a predefined height. The first weir means 217 comprises a first weir wall 218 for allowing the first overflow of oil to flow from the intermediate volume 208 over the first weir wall 218 into the primary volume 206. The first weir wall 218 may be provided by the first wall 211, which is configured to allow an overflow of oil over the top of the first wall 211 or through an aperture formed in the first wall 211. In an alternative embodiment, the first weir wall 218 comprises a wall of a duct extending between the intermediate volume 208 and the primary volume 206. For example, the duct may be provided by an overflow pipe. In the embodiment of FIGS. 2 and 3, the first weir wall 218 comprises an element attached to the first wall 211 that extends upwards from the top of the first wall 211.

[0079] During operation of the engine 102, oil is pumped from the sump 103 via the outlet 209 to various parts of the engine 102 as is known. Returned oil falls back down into the sump 103 to be reused, and at least a portion of the returned oil falls towards the secondary volume, as indicated by arrows 221. However, the oil sump 103 also comprises a top-up arrangement 219 configured to direct returned oil to a top-up port 220 of the secondary volume 207 and also enable excess returned oil to overflow into the intermediate volume 208. As used herein, the expression excess returned oil means oil returned from the engine 102 and available to fill the secondary volume but which cannot be accommodated by the secondary volume 207 due to it being full.

[0080] The top-up arrangement 219 comprises a second weir means 222 positioned to enable the excess returned oil to overflow into the intermediate volume 208. The top-up arrangement 219 also comprises a first cover wall 223, which is positioned over the secondary volume 207. The first cover wall 223 has an outer surface 224 that is sloped to direct oil falling on the outer surface 224 towards the top-up port 220 and towards the intermediate volume 208 via the second weir means 222.

[0081] In the embodiment of FIGS. 2 and 3, the first cover wall 223 defines an aperture 220 which provides the top-up port 220, to enable oil to flow from the outer surface 224 into the secondary volume 207.

[0082] The second weir means 222 comprises a second weir wall 225 for allowing excess returned oil to flow over the second weir wall 225 into the intermediate volume 208. I.e., the second weir wall 225 is arranged to allow oil to overflow into the intermediate volume 208 when the level of oil in the secondary volume 207 is at or above a second height. In the present embodiment the second height is substantially level with the first height of the first weir wall 218 but in other embodiments the first height may be higher than the second height, so that when the intermediate volume is full of oil the levels of oil in the intermediate volume 208 and the secondary volume 207 are equal.

[0083] In the embodiment of FIGS. 2 and 3, the second weir wall 225 is provided by an end portion of the first cover wall 223 that is disposed above the second wall 212.

[0084] In an alternative embodiment the second wall 212 may provide the second weir wall 225, which is configured to allow an overflow of oil over the top of the second wall 212 or through an aperture formed in the second wall 212. Alternatively, the second weir wall 225 may comprise a wall of a duct extending between the secondary volume 207 and the intermediate volume 208. For example, the duct may be provided by an overflow pipe.

[0085] The first cover wall 223 may be contoured to direct oil from the whole of its width 226 towards the top-up port 220, and/or as shown in FIGS. 2 and 3, a barrier wall 227, that is higher than the second weir wall 225, may be provided to prevent oil from running off the outer surface 224 at positions that are distant from the top-up port 220. Consequently, all oil flowing down the outer surface 224 must pass through the top-up port 220, or over or adjacent to the top-up port 220 before flowing over the second weir wall 225.

[0086] The sump 103 may comprise a second cover wall 228 that slopes from an upper end, downwards over the primary volume 206, the intermediate volume 208 and a part of the first cover wall 223, to a lower end over the first cover wall 223. Thus, during use, oil falling towards the primary volume 206 and the intermediate volume 208 falls onto the second cover wall 228 and runs down the second cover wall 228 onto the first cover wall 223. In this way, all oil that is returned to the sump 103 may be directed towards the top-up port 220. In other embodiments, alternative means of directing all returned all to the first cover wall 223 may be provided.

[0087] Various stages of the operation of the oil sump 103 during operation of the engine 102 are illustrated in the cross-sectional views of FIGS. 4, 5 and 6. In each of the FIGS. 4, 5 and 6 the sump contains motor oil 401. In FIG. 4, the oil 401 has the same level in each of the three volumes 206, 207 and 208. This situation exists when the engine 102 has been switched off for a period of time, so that the oil levels in each of the three volumes has been able to equalize by flowing through the restricted flow means 214 and 216.

[0088] When the engine 102 is first started and oil 401 is pumped out of the primary volume 206, the oil level in the primary volume 206 falls. At this stage, the oil 401 is cold and relatively viscous, and the flow through the meshes 214A and 216A is limited to a relatively low rate of flow compared to the rate at which oil 401 is pumped from the primary volume 206. Oil 401 pumped from the primary volume 206 lubricates the engine 102 but eventually falls back down towards the sump 103, where at least a portion of the returning oil falls on the first cover wall 223.

[0089] The returned oil 401 runs down the outer surface 224 of the first cover wall 223 towards the intermediate volume 208. However, initially the returned oil drops through the top-up port 220 and begins to fill the secondary volume 207. When the secondary volume 207 is full and the level of oil 401 has reached the top of the second weir wall 225, the oil overflows the second weir wall 225 and begins to fill the intermediate volume 208. When the intermediate volume is full and the level of oil 401 in the intermediate volume 208 has reached the top of the first weir wall 218, the oil overflows the first weir wall 218 and returns to the primary volume 206. This situation is shown in FIG. 5.

[0090] Thus, in FIG. 5 the secondary volume 207 and the intermediate volume 208 are full of oil 401 and the level of oil in the primary volume 206 has dropped in comparison to the initial level shown in FIG. 4. A first portion 501 (shown in dotted outline) of the oil 401 lost from the primary volume 206 represents the oil that has been used to top up the secondary volume 207 and the intermediate volume 208. A second portion 502 (shown in dotted outline) of the oil 401 lost from the primary volume 206 represents oil that is stuck around the wetted areas of the engine 102.

[0091] Typically, the state shown in FIG. 5 is achieved within 15 to 40 seconds of the engine 102 being started, while the oil 401 is still relatively cool. From that time onwards, additional returned oil falling on the first cover wall 223 generally flows over the second weir wall 225 and the first weir wall 218 back to the primary volume 206. As the engine 102 is run, the oil 401 circulated around the engine 102 and returned to the primary volume 206 is heated up by the engine 102, but the oil 401 in the secondary volume 207 and the intermediate volume 208 remains relatively stagnant and cool. Because only the relatively small volume of oil 401 in the primary volume 206 is being repeatedly circulated around the engine 103 at this stage, the oil 401 in the primary volume 206 reaches higher temperatures more quickly than it would do if all of the oil 401 were being circulated around the engine 103. Consequently, the viscosity of the oil 401 used to lubricate the engine 102 reduces more rapidly than it would if all of the oil 401 were being circulated, and so the efficiency of the engine 102 similarly increases more rapidly.

[0092] Because the first weir wall 218 and the second weir wall 225 extend up to about the same height, the levels of oil 401 in the secondary volume 207 and the intermediate volume 208 are substantially equal, and there is no difference in pressure of the oil from one side of the second flow restriction means 216 to the other side. Consequently, there is no leakage of oil 401 from the secondary volume 207 to the intermediate volume 208 through the second flow restriction means 216.

[0093] When the intermediate volume 208 is first filled with oil 401, the oil in the intermediate volume 208 is relatively cold and has a high viscosity. Consequently, oil only leaks slowly through the first mesh 214A, and so only a relatively small amount of cold oil from the intermediate volume 208 is mixed into the relatively hot oil in the primary volume 206. It may be noted that, while almost all oil 401 that flows over the second weir wall 225 also flows over the first weir wall 218 into the primary volume 206, a portion of the oil flowing over the second weir wall 225 tops up the intermediate volume 208 to maintain its oil at the same level as that of the secondary volume 207.

[0094] The temperature of oil in the intermediate volume 208 rises slowly due to conduction through the first wall 211 and the first flow restricting means 214 and also due to the small quantities of hot oil used to top up the intermediate volume 208. As its temperature rises, the viscosity of oil 401 in the intermediate volume 208 reduces and the rate of leakage of oil through the mesh 214A increases. Consequently, the portion of oil flowing over the second weir wall 225 that is used to top up the intermediate volume 208 increases while the portion flowing over the first weir wall 218 decreases, until the rate of oil flowing through the first mesh 214A is greater than the rate of oil flowing over the second weir wall 225. When this happens, the level of oil 401 in the intermediate volume 208 begins to drop and oil no longer flows over the first weir wall 218.

[0095] In an alternative embodiment, a baffle or cover 503 (shown in dashed outline in FIG. 5) is provided that extends over a lower first portion 504 of the intermediate volume 208. A hole 506 provides a passageway between a second portion 505 of the intermediate volume 208, which is above the cover 503 of the first portion 504. The hole 506 is provided to enable oil to run down from the second portion 505 of the intermediate volume 208 past the cover 503 to allow the initial filling of the intermediate volume 208. The hole 506 may be formed in the cover 503 or may be provided between the cover 503 and the first wall 211, as shown in FIG. 5, or may be provided between the cover 503 and the second wall 212.

[0096] When the intermediate volume 208 is full, as shown in FIG. 5, the cover 503 resists mixing of the hot oil 401 that flows over the second weir wall 225 with the relatively cold oil 401 in the first portion 504 of intermediate volume 208. Consequently, oil 401 in the relatively small second portion 505 of the intermediate volume 208 may be warmed while oil in the first portion 504 adjacent to the mesh 214A, warms up more slowly. Consequently, the presence of the baffle or cover 503 may increase the period of time from the engine 102 being started until the level in the intermediate volume 208 begins to fall.

[0097] When the level of oil 401 in the intermediate volume 208 drops to below the level in the secondary volume 207 a difference in pressure is produced across the second mesh 216A that causes the oil 401 to begin flowing from the secondary volume 207 through the second mesh 216A into the intermediate volume 208. Oil in the secondary volume 207 is topped-up with hot oil flowing down the first cover wall 223 and through the top-up port 220.

[0098] When the rate of flow of oil 401 through the second mesh 216A becomes greater than the rate at which oil is topping up the secondary volume 207, the level of oil 401 in the secondary volume 207 begins to drop. FIG. 6 shows the oil sump 103 at this stage, in which the level of oil 401 in the intermediate volume 208 has dropped and consequently the level of oil 401 in the secondary volume 207 has begun to drop. From this time onwards substantially all of the oil 401 returned to the first cover wall 223 falls through the top-up port 220 into the secondary volume 207, and oil 401 flows through the second mesh 216A and the first mesh 214A to the primary volume 206, where it is recirculated via the outlet 209. Thus, all of the oil 401 in the oil sump 103 is then used to lubricate the engine 102.

[0099] When the engine 102 is stopped, oil 401 drains back down into the sump 103 and the levels of oil in the three volumes 206, 207 and 208 equalize, so that the sump 103 is once again as shown in FIG. 4.

[0100] It should be understood from the above description that: the operation of the sump 103 enables a relatively small portion of the oil 401 to lubricate the engine 102 when the engine 102 is first switched on, so that the oil 401 used at this stage reaches higher temperatures more quickly and the efficiency of the engine is improved; all oil is eventually used and circulated around the engine 102; and the portion of oil 401 present in the primary volume 206 at the end of use is not the same portion of oil that was present in the primary volume 206 at the start of use.

[0101] An alternative oil sump 103 for the engine 102 is shown in a perspective view in FIG. 7 and a cross-sectional view in FIG. 8. The oil sump 103 of FIGS. 7 and 8 has many of the same features as the oil sump 103 of FIGS. 2 to 6, and features that are common to both sumps 103 have been labelled in the same way. Thus, the oil sump of FIGS. 7 and 8 comprises a container 202 that defines a volume 205 for containing oil (not shown in FIGS. 2 and 3). The volume 205 comprises three volumes: a primary volume 206; a secondary volume 207; and an intermediate volume 208. The primary volume 206 is suitable for containing an oil outlet 209 (shown in FIG. 8) on a pickup tube 210, or an oil pump, to enable oil to be pumped from the sump 103 during use.

[0102] A first wall 211 divides the primary volume 206 from the intermediate volume 208, and a second wall 212 divides the secondary volume 207 from the intermediate volume 208. The first wall 211 comprises a first restricted flow means 214 configured to enable a restricted flow of oil from the intermediate volume 208 to the primary volume 206. The first restricted flow means 214 differs from that of FIGS. 2 and 3 in that it comprises a trap door 214B rather than a mesh. The trap door 214B comprises actuation means configured to cause the door to remain closed for temperatures up to a first threshold temperature and to open as the temperature rises above the first threshold temperature. In the present embodiment the trap door 214B is actuated by a bimetallic strip. The bimetallic strip may be of a type that is typically produced for electrical safety cut-outs or thermostats.

[0103] The trap door 214B may be configured to allow some leakage of oil when it is closed but allow a much greater flow when it is open.

[0104] The second wall 212 comprises a second restricted flow means 216 configured to enable a restricted flow of oil from the secondary volume 207 to the intermediate volume 208. The second restricted flow means 216 is configured to provide a passageway for a flow of oil from the secondary volume 207 to the intermediate volume 208 when oil adjacent to the second restricted flow means 216 is above a second threshold temperature. The second restricted flow means 216 may be configured to allow a slower flow of oil for temperatures below the second threshold temperature. The second threshold temperature may be equal to the first threshold temperature. In the present embodiment, the second restricted flow means 216 comprises a mesh 216A, like that of FIGS. 2 and 3.

[0105] The oil sump 103 also comprises a first weir means 217 that is positioned to enable a first overflow of oil from the intermediate volume 208 into the primary volume 206 when oil within the intermediate volume is above a predefined height. In the present embodiment, the first wall 211 provides the function of the first weir means 217. I.e. when the intermediate volume 208 is full, oil is able to overflow the first wall 211 into the primary volume 206.

[0106] The oil sump 103 of FIGS. 7 and 8 also comprises a top-up arrangement 219 configured to direct returned oil to two top-up ports 220 of the secondary volume 207 and also to enable excess returned oil to overflow into the intermediate volume 208. The top-up arrangement 219 comprises a second weir means 222 positioned to enable excess returned oil to overflow into the intermediate volume 208. The top-up arrangement 219 also comprises a first cover wall 223, which is positioned over the secondary volume 207, and which has an outer surface 224 that is sloped to direct oil falling on the outer surface 224 towards the intermediate volume 208 via the second weir means 222.

[0107] In the embodiment of FIGS. 7 and 8, a trough 802 is positioned towards the lower end of the first cover wall 223 and the top-up ports 220 each comprise a bore of a tube 803 that extends downwards from the bottom of the trough 802. A deflection means 804, comprising a baffle, is positioned below the ends of the tubes 803 and is configured to deflect oil flowing from the tubes 803 away from the mesh 216A.

[0108] The second weir means 222 comprises a second weir wall 225 for allowing excess returned oil to flow over the second weir wall 225 into the intermediate volume 208. In the embodiment of FIGS. 7 and 8, the second weir wall 225 is provided by a side wall of the trough 802.

[0109] The first cover wall 223 is provided with an upwardly extending breather tube 805 that has a breather aperture 806 near to its uppermost end. The breather tube 805 is provided to ensure air can escape from the secondary volume 207 during filling with oil.

[0110] The oil sump 103 of FIGS. 7 and 8 also comprises a cover 801 which covers a first portion 504 of the intermediate volume 208. The cover 801 defines two holes 807 which extend from an second portion 505 of the intermediate volume 208, which is above the cover 801, to the first portion 504. The holes 807 are dimensioned to limit the rate of flow of oil into the first portion 504 of the intermediate volume 208 such that the holes 807 provide a higher resistance to flow of oil than the first flow restriction means 214 for temperatures above the threshold temperature. I.e. when the trap door 214B is open, it is configured to provide less resistance to flow of oil into the primary volume 206 than the resistance to flow provided by the holes 807.

[0111] The oil sump 103 of FIGS. 7 and 8 may be provided with a second cover wall, like the second cover wall 228 described above with regard to FIG. 3.

[0112] Various stages of the operation of the oil sump 103 of FIGS. 7 and 8 during operation of the engine 102 are illustrated in the cross-sectional views of FIGS. 9, 10, 11 and 12. In each of the FIGS. 9, 10, 11 and 12 the sump 103 contains motor oil 401. In FIG. 9, the trap door 214B is in the closed position and the oil 401 has the same level in each of the three volumes 206, 207 and 208. This situation exists when the engine 102 has been switched off for a period of time, so that the oil levels in each of the three volumes 206, 207 and 208 have been able to equalize by flowing through the trap door 214B and the mesh 216A. The equalization may occur while the oil 401 is hot and the trap door 214B is open. Alternatively, for example when the engine 102 was only previous used for a very brief period of time and the trap door 214B did not open, the equalization may occur by leakage of oil past the trap door 214B in its closed position.

[0113] When the engine 102 is first started, oil 401 is pumped out of the primary volume 206 via the pickup tube 210 to lubricate the engine 102. Returned oil 401 falling on the first cover wall 223 flows down the first cover wall 223 and into the second volume 207, via the trough 802 and the top-up ports 220, until the secondary volume 207 is full. When the second volume 207 is full, the top-up ports 220 (i.e., the bores of the tubes 803) and the trough 802 also contain oil 401. With the secondary volume 207 full, oil 401 begins to overflow the second weir wall 225 onto the cover 801 disposed in the intermediate volume 208 and begins filling the intermediate volume 208. When the intermediate volume 208 is full, the oil 401 then overflows the first weir wall 218 into the primary volume 206.

[0114] From then onwards, most of the oil 401 that is pumped from the primary volume 206 around the engine 102 and returned to the first cover wall 223 returns to the primary volume 206 via the first and second weir walls 218 and 225. Consequently the relatively small volume of oil 401 that is pumped around the engine 102 heats up quickly while the oil 401 in the secondary volume 207 and intermediate volume 208 remains cold and stagnant.

[0115] The oil sump 103 is shown in FIG. 10 with the secondary volume 207 and the intermediate volume 208 full of oil 401 and excess oil flowing over the second weir wall 225 and the first weir wall 218 into the primary volume 206. The level of oil 401 in the secondary volume 207 is substantially equal to the level in the intermediate volume 208. Therefore there is substantially no pressure difference from one side of the mesh 216A to its other side and no flow of oil through the mesh 216A.

[0116] Due to the closed trap door 214B not providing a perfect seal, when the intermediate volume 208 is full, some oil 401 may leak from the intermediate volume 208 past the trap door 214B into the primary volume 206. However, the intermediate volume 208 is topped-up by a portion of the oil 401 overflowing the second weir wall 225. The holes 807 in the cover 801 are sufficiently large to enable a rate of flow that is at least equal to the rate at which oil leaks past the closed trap door 214B, and so the intermediate volume 208 is kept topped up.

[0117] With the sump 103 in the state as shown in FIG. 10, hot oil returning to the sump 103 may mix with the small quantities of oil in the trough 802 and the second portion 505 of the intermediate volume 208. The larger quantity of oil in the secondary volume 207 remains cold and relatively undisturbed by the returning oil. Also, only a relatively small quantity of warmed oil passes through the holes 807 in the cover 801 to the first portion 504 of the intermediate volume 208 to compensate for the oil leaking past the closed trap door 214B. In contrast, oil in the primary volume 206 of the sump 103 is repeatedly pumped through the pickup tube 210 and used to lubricate the engine 102 as the engine warms up. Consequently the oil 401 in the primary volume 206, which is used to lubricate the engine 102, warms up relatively quickly, and similarly its viscosity falls relatively quickly.

[0118] When the engine 102 and the oil 401 in the primary volume 206 becomes sufficiently hot, the trap door 214B reaches a threshold temperature at which it is moved into its open position. This results in an increased rate of flow of oil from the intermediate volume 208 through the trap door 214B into the primary volume 206. The holes 807 in the cover 801 are dimensioned to provide a greater resistance to the rate of flow of oil than the open trap door 214B and so the quantity of oil in the intermediate volume 208 begins to fall. As the quantity of oil in the intermediate volume 208 reduces, a pressure difference appears across the mesh 216A, which causes the cold oil in the secondary volume 207 to flow through the mesh 216A into the intermediate volume 208. The flow through the mesh 216A causes the level in the secondary volume 207 to fall and so hot oil returning to the first cover wall 223 flows into the secondary volume 207 rather than flowing over the second weir wall 225.

[0119] In an alternative embodiment the cover 801 may be provided with one or more breather tubes that extend upwards from the general level of the cover 801 to height above the level that is locally attained by the oil 401. The breather tubes enable air to escape from the second volume 207 as oil 401 flows into the second volume.

[0120] The sump 103 is shown in FIG. 11 with the trap door 214B open, the level in the intermediate volume 208 reduced to be approximately the same as that in the primary volume 206 and all returned oil 401 flowing into the secondary volume 207. From then onwards, returned oil flows through the secondary volume 207, the mesh 216A to the intermediate volume 208 and the trap door 214B to the primary volume 206, and therefore all of the oil 401 is used to lubricate the engine 102.

[0121] When the engine 102 is turned off, oil in the three volumes 206, 207 and 208 is able to equalize as shown in FIG. 12. When the oil 401 has cooled sufficiently, the trap door 214B closes and the sump returns to the state shown in FIG. 9.

[0122] Another alternative sump 103 embodying the present invention is shown in use in FIG. 13. The sump 103 of FIG. 13 is identical to that described with reference to FIGS. 7 to 12, except the trap door 214B is replaced by a mesh 214A, which provides a restricted flow means 214 between the intermediate volume 208 and the primary volume 206. In this embodiment, when the oil 401 is relatively cold, the holes 807 in the cover 801 are sufficiently large to enable oil 401 to flow through them at a rate that is equal to the flow through the mesh 214A, and so the intermediate volume 208 may be kept topped up, as shown in FIG. 13. However, when the oil 401 adjacent to the mesh 214A reaches a threshold temperature, the rate of flow through the mesh 214A becomes greater than that allowed by the holes 807 in the cover 801, and so the level of oil 401 in the intermediate volume 208 drops

[0123] In the above described embodiments, the oil 401 returned to the first cover wall 223 is directed to the intermediate volume 208 and oil overflows from the intermediate volume into the primary volume 207. However, in an alternative embodiment, oil 401 is permanently prevented from overflowing from the intermediate volume 208 into the primary volume 206 by a relatively high wall. A first weir wall is provided between the first cover wall 223 and the primary volume 206, and a second weir wall 225 is provided between the first cover wall 223 and the intermediate volume 208. The first weir wall is higher than the second weir wall 225, and so the intermediate volume 208 and the secondary volume 207 are topped up to the height of the first weir wall and then surplus oil overflows into the primary volume 206.

[0124] An embodiment of the engine 102 comprising an alternative oil sump 103A is shown in the somewhat schematic view of FIG. 14. In the present embodiment, the engine 102 comprises four cylinders 1402, each containing a respective piston 1403. Thus, cylinder 1402A contains a piston 1403A, cylinder 1402B contains a piston 1403B, cylinder 1402C contains a piston 1403C, and cylinder 1402D contains a piston 1403D. Each cylinder 1402 in combination with its respective piston 1403 defines a combustion chamber.

[0125] Each of the pistons 1403 is connected to a crankshaft 1404 by a respective connecting rod 1405. The crankshaft 1404 is located within a crankcase 1401 and it is supported by front and rear main bearings and also by intermediate bearings located within internal walls 1406, which divide space within the crankcase 1401 into four separate bays 1407. During operation of the engine 102, the bays 1407 contain air that is contaminated with blow-by gases escaping from the combustion chambers and droplets of oil used to lubricate moving parts of the engine 102. For the purposes of the present specification the mixture of air, blow-by gases and oil droplets will simply be referred to as air.

[0126] The interior of the sump 103A is separated from the bays 1407 by an upper sump wall 1420 of the sump 103A, which provides an end wall of the bays 1407.

[0127] During operation of the engine 102, the reciprocating motion of the pistons 1402 causes the volume of each of the bays 1407 to repeatedly change. To avoid compression of the air within the bays 1407, passageways may be provided between neighboring bays 1407 through the internal walls 1406. However, in the present embodiment, bay-to-bay breathing is provided via the oil sump 103A by slots 1408 formed in the upper sump wall 1420 of the sump 103A. One or more slots 1408 are provided in the upper sump wall 1420 at the lower end of each one of the bays 1407. I.e., in the present embodiment, in which the engine has four bays 1407, one or more slots 1408A are positioned at the end of a first bay 1407A, one or more slots 1408B are positioned at the end of a second bay 1407B, one or more slots 1408C are positioned at the end of a third bay 1407C, and one or more slots 1408D are positioned at the end of a fourth bay 1407D.

[0128] During operation, the pistons 1403A and 1403D are lowered, decreasing the volume of the first bay 1407A and the fourth bay 1407D, and the pistons 1403B and 1403C are simultaneously raised, increasing the volume of the second bay 1407B and the third bay 1407C. This causes air to be forced through the first slot(s) 1408A and the fourth slot(s) 1408D allowing air to escape from the first and fourth bays, 1407A and 1407D, into the sump 103A and out through the second slot(s) 1408B and the third slot(s) 1408C into the second and third bays, 1407B and 1407C. Subsequently, as the pistons 1403B and 1403C are lowered, decreasing the volume of the second bay 1407B and the third bay 1407C, and the pistons 1403A and 1403D are simultaneously raised, increasing the volume of the first bay 1407A and the fourth bay 1407D, air is forced through the second slot(s) 1408B and the third slot(s) 1408C allowing air to escape from the second and third bays, 1407B and 1407C, into the sump 103A and out through the first slot(s) 1408A and fourth slot(s) 1408D into the first and fourth bays, 1407A and 1407D.

[0129] In this manner air is pumped between the bays 1407 backwards and forwards through the sump 103A. The sump 103A comprises baffles 1421 and 1422 (illustrated schematically in FIG. 14) configured to cause the air pumped through the sump 103A to take a circuitous route that causes separation of the oil droplets from the air in which they are supported.

[0130] A plan view of the sump 103A with the upper sump wall 1420 in place is shown in FIG. 15, and a plan view of the sump 103A with the upper sump wall 1420 removed is shown in FIG. 16. For the sake of clarity, some features within the sump 103A have been omitted from the plan view of FIG. 15. The positions of the interior walls 1406 of the engine 102 are illustrated by dotted lines in FIG. 15.

[0131] In the embodiment of FIG. 15, one slot 1408 is provided in the upper sump wall 1420 at the lower end of each of the four bays 1407. In alternative embodiments, several slots 1408 are provided for each of the bays 1407.

[0132] The oil sump 103A comprises a first plurality of baffles 1421 which define a corresponding number of outer chambers 1501. A first baffle 1421A separates a first outer chamber 1501A of the sump 103A from a fourth outer chamber 1501D of the sump 103A; a second baffle 1421B separates the first outer chamber 1501A from a second outer chamber 1501B of the sump 103A; a third baffle 1421C separates the second outer chamber 1501B from a third outer chamber 1501C of the sump 103A; and a fourth baffle 1421D separates the third outer chamber 1501C from the fourth outer chamber 1501D.

[0133] Each of the baffles 1421 extend inwards from a respective first position 1502 adjacent to the outer wall 204 of the sump 103A to a second position 1503 adjacent to a pickup chamber 1504 containing an oil outlet 1505 of a pickup tube 1506. A gap 1507 is provided between the second positions 1503 of neighboring ones of the baffles 1421 enable flow of oil from the outer chambers 1501 to the pickup chamber 1504 during use.

[0134] In the embodiment of FIG. 15, the oil sump 103A also comprises a second plurality of baffles 1422 that are different to the first plurality of baffles 1421. The second plurality of baffles 1422 are in the form of a ring of louvres which reside on a curve extending across the gaps 1507 between the second positions 1503 of the first baffles 1421 to provide walls of the pickup chamber 1504. The second plurality of baffles 1422 divide up each of the gaps 1507 into several (in this embodiment 6) slots. The baffles 1422 are angled to the curve on which they reside so that the width of the louvre extends from an outer edge to an inner edge in the same rotational direction around the pickup chamber 1504. Thus, in use, the baffles 1422 cause fluid flowing from each one of the outer chambers 1501 into the pickup chamber 1504 to flow in the same rotational direction around the pickup chamber 1504.

[0135] In the present embodiment, the second plurality of baffles 1422 comprises 24 baffles arranged to divide each of the four gaps 1507 into six slots. However, other quantities of baffles 1422 are provided in alternative embodiments. For example, in alternative embodiments, just one baffle 1422 is positioned within each of the gaps between neighboring ones of the first plurality of baffles 1421. For example, in an embodiment the sump has four of the first baffles 1421 and four of the second baffles 1422.

[0136] In the embodiment of FIG. 15, each outer chamber 1501 is able to receive a flow of air (containing oil droplets) from the bays 1407 of the engine 102 via a respective slot 1408. The slots 1408 are positioned within the upper sump wall 1420 so that each outer chamber 1501 receives air from a respective one of the bays 1407. In the present embodiment, the second outer chamber 1501B receives air via the first slots 1408A from the first bay 1407A; the third outer chamber 1501C receives air via the second slots 1408B from the second bay 1407B; the first outer chamber 1501A receives air via the third slots 1408C from the third bay 1407C; and the fourth outer chamber 1501D receives air via the fourth slots 1408D from the fourth bay 1407D.

[0137] During operation of the engine 102, oil is pumped out of the sump 103A through the pickup tube 1506 via the outlet 1505 in the pickup chamber 1504. Consequently, oil flows from the outer chambers 1501 through the gaps 1507 into the pickup chamber 1504. The second plurality of baffles 1422 cause oil entering the pickup chamber 1504 to flow in a clockwise direction around the pickup chamber 1504, which causes a continuous clockwise motion of oil within the pickup chamber 1504.

[0138] A portion of the oil entering the pickup chamber 1504 may be in the form of foam floating on the top of the bulk of the oil. The clockwise flow of the oil within the pickup chamber 1504 has a centrifugal-type effect, in that the denser component of the foam, i.e. the oil, is forced towards the outside of the flow where it coalesces with the bulk of the oil, and the lighter component, i.e. air, is forced inwards towards the middle of the pickup chamber 1504. Thus, the circular flow of oil within the pickup chamber 1504 assists the removal of air from the oil before it is pumped around the engine 102.

[0139] When the pistons 1403A and 1403D (shown in FIG. 14) are lowered, air is forced out of the bays 1407A and 1407D through slots 1408A and 1408D into the outer chambers 1501B and 205D of the oil sump 103A. Simultaneously, air is drawn into the bays 1407B and 1407C from the outer chambers 1501C and 205A. Consequently, air is pumped through the pickup chamber 1504 as illustrated in FIG. 17, which shows flows around the baffles 1421 and 1422 in the vicinity of the pickup chamber 1504. Specifically, air containing oil droplets is forced into the pickup chamber 1504 from the outer chamber 1501B through the slots between the baffles 1422 that are between the baffles 1421B and 1421C and air is also forced into the pickup chamber 1504 from the outer chamber 1501D between the baffles 1421A and 1421D.

[0140] Simultaneously, air is drawn out of the pickup chamber 1504 into the outer chambers 1501A and 1501C. The flows of air entering the pickup chamber 1504 from outer chambers 1501B and 1501D are relatively focused and have a direction that is substantially in a clockwise direction around the pickup chamber 1504. In contrast, the air entering the outer chambers 1501A and 1501C is drawn from the pickup chamber 1504 over a wider range of angles. Consequently, the net flow of mass of air within the pickup chamber 1504 is clockwise as in indicated by circular arrows 1701.

[0141] In addition, the relatively high inertia of oil droplets suspended in the air in the pickup chamber 1504, tends to cause the oil droplets to continue on a path past the slots between the baffles 1422 and to remain within the pickup chamber 1504. Consequently, the air drawn out of the pickup chamber 1504 into outer chambers 1501 and 1501C is relatively free of oil when compared to the air entering the pickup chamber 1504 from outer chambers 1501B and 1501D.

[0142] Similarly, when the pistons 1403B and 1403C (shown in FIG. 14) are lowered, air is forced out of the bays 1407B and 1407C through slots 1408B and 1408C into the outer chambers 1501C and 1501A (shown in FIG. 15) of the oil sump 103A. Simultaneously, air is drawn into the bays 1407A and 1407D from the outer chambers 1501B and 1501D as the pistons 1403A and 1403D are raised. Consequently, air is pumped through the pickup chamber 1504 as shown in FIG. 18. Specifically, air containing oil droplets is forced into the pickup chamber 1504 from the outer chamber 1501A through the slots between baffles 1422 that are between the baffles 1421A and 1421B and air is also forced into the pickup chamber 1504 from the outer chamber 1501C between the baffles 1421C and 1421D.

[0143] Simultaneously, air is drawn out of the pickup chamber 1504 into the outer chambers 1501B and 1501D. The flows of air entering the pickup chamber 1504 from outer chambers 1501A and 1501C are relatively focused and have a direction that is substantially in a clockwise direction around the pickup chamber 1504. In contrast, the air entering the outer chambers 1501B and 1501D is drawn from the pickup chamber 1504 over a wider range of angles. Consequently, the net flow of mass of air within the pickup chamber 1504 is clockwise as in indicated by circular arrows 1701.

[0144] Because the net airflow within the pickup chamber 1504 is clockwise for both upward strokes and downward strokes of each piston 1403, the oil droplets suspended in the air circulating within the pickup chamber 1504 are able to attain high speeds and their momentum tends to force them outwards towards the surrounding wall of the pickup chamber 1504, which is provided by the baffles 1422. Oil droplets colliding with the baffles 1422, other oil droplets or the bulk of the oil within the pickup chamber 1504 are able to coalesce with other droplets or the bulk of the oil. Also, because the oil droplets are forced outwards and removed from the circulating air, the air towards the middle of the pickup chamber 1504 becomes relatively free of oil droplets.

[0145] Another feature of the oil sump 103A is illustrated in FIG. 16. Like the oil sumps 103 of FIGS. 2 to 13, the oil sump 103A of FIGS. 15 and 16 comprises a first wall 211 dividing a primary volume 206 from an intermediate volume 208, and a second wall 212 dividing a secondary volume 207 from the intermediate volume 208. However, in the present embodiment, the first wall 211 extends around the periphery of the primary volume 206, which contains the baffles 1422 and the pickup chamber 1504. Similarly, the second wall 212 extends around the outside of the intermediate volume 208, which extends around the primary volume 206. The secondary volume 207 extends around the outside of the second wall 212.

[0146] The first wall 211 and the second wall 212 are divided into four sections by the baffles 1421. The baffles 1421 also divide the secondary volume 207 into four parts and divide the intermediate volume 208 into four parts. Consequently, each of the outer chambers 1501 is divided by the first wall 211 and the second wall 212 into a first part, which forms part of the primary chamber 206, a second part which forms a part of the intermediate volume 208 and a third part which forms a part of the secondary volume 207.

[0147] A somewhat schematic cross-sectional view of the sump 103A is shown in FIG. 19, which shows the first wall 211 and the second wall 212 within the outer regions 1501 and 1501C. In the present embodiment, the whole of the first wall 211 and the second wall 212 are formed of a mesh material. The second wall 212 comprises two layers 1901 and 1902 of mesh with a second intermediate volume 1903 between the two layers. The secondary volume 207 has a first cover wall 1904 which is also formed of a mesh. The first cover wall 1904 has a concaved outer surface 1905 which extends up to a high portion 1906 to form a second weir means 222. The first cover wall 1904 and the second weir means 222 provides a top-up arrangement 219 configured to enable returned oil to flow through the holes in the mesh forming the first cover wall 1904 into the secondary volume 207 and also enable excess returned oil to overflow into the intermediate volume 208.

[0148] A cover 1907 is provided over a lower first portion 1908 of the intermediate volume 208. The cover 1907 is also formed of a mesh, and the cover has a concave outer surface 1909 which slopes upwards to a high portion 1910 that forms a first weir means 217. The concave outer surface 1909 of the cover 1907 defines an second portion 1911 of the intermediate volume 208 which temporarily contains oil during use, as will be described below.

[0149] In the embodiment of FIG. 19, the first wall 211, both layers 1901 and 1902 of the second wall 212, the first cover wall 1904 and the cover 1907 in each of the outer chambers 1501 is formed of a single sheet of mesh material that is pressed into a shape to provide those features 211, 212, 1904 and 1907. During use of the oil sump 103A, oil is able to flow between the secondary volume 207 and the intermediate volume 208, and between the intermediate volume 208 and the primary volume 206 through the apertures formed in the mesh material. Thus, the mesh material forming the first wall 211 and the mesh material forming the second wall 212 provides a first restricted flow means 214 and a second restricted flow means 216 respectively.

[0150] It should be understood that the first wall 211, the second wall 212, the first cover wall 1904 and the cover 1907 in the outer chamber 1501A extend from the first baffle 1421A to the second baffle 1421B. Similarly the first wall 211, both layers 1901 and 1902 of the second wall 212, the first cover wall 1904 and the cover 1907 in the other outer chambers 1501 extend between the two baffles 1421 that define those outer chambers 1501.

[0151] The mesh material providing the features 211, 212, 1904 and 1907 may be formed of woven metal wires that are sufficiently stiff to maintain the shape illustrated in FIGS. 16 and 19. Alternatively the mesh material may be formed of polymer fibres. In some embodiments, the mesh material may be supported by a polymer frame that is molded onto the mesh material in the required shape, so that the mesh material extends between sections of the frame. In alternative embodiments, instead of the first cover wall 1904 and the cover 1907 comprising mesh material, each of the outer chambers 1501 contains a structure similar to that illustrated and described with reference to FIGS. 2 to 6 or 7 to 13.

[0152] The baffles 1421 may be formed as an integral part of the container 202. For example, the container 202 and the baffles 1421 may be formed from a composite material or a metal alloy in a single molding process.

[0153] As described above, air blown into, and drawn out of, the sump 103A via the slots 1408 in the upper sump wall 1420, causes air to be blown from the outer chambers 1501 into the pickup chamber 1504 and to be drawn out of the pickup chamber 1504 into the outer chambers 1501.

[0154] Due to the presence of the first cover wall 1904 and the cover 1907, the air generally enters the pickup chamber 1504 from an elevated position above the first weir means 217.

[0155] In the present embodiment, the sump 103A comprises an air deflection means 1912 that extends downwards from the upper sump wall 1420 adjacent to the second plurality of baffles 1422. The air deflection means 1912 may form a part of the upper sump wall 1420 or a part of an element comprising the ring of louvres, i.e. baffles 1422. The air deflection means 1912 comprises a curved surface 1913 configured to deflect air downwards as it flows from the outer chambers 1501 into the pickup chamber 1504. Consequently, during operation of the engine 102, airborne oil droplets carried into the pickup chamber 1504 are projected downwards towards the bulk of the oil in the pickup chamber 1504. In contrast, when air is drawn from the pickup chamber 1505 into an outer chamber 1501, the air is drawn from a range of heights of the pickup chamber 1504, including the upper end of the pickup chamber 1504 where the concentration of airborne oil droplets is relatively low. This therefore provides another mechanism to cause air drawn from the pickup chamber 1504 to be cleaner than the air blown into it.

[0156] The oil sump 103A is illustrated in use in FIGS. 20, 21 and 22. In each of the FIGS. 20 to 22 the sump contains engine oil 401. In FIG. 20, the oil 401 has the same level in each of the three volumes 206, 207 and 208. This situation exists when the engine 102 has been switched off for a period of time, so that the oil levels in each of the three volumes has been able to equalize by flowing through the first wall 211 and the second wall 212.

[0157] When the engine 102 is first started and oil 401 is pumped out of the primary volume 206, via the outlet 1505 and the pickup tube 1506, the oil level in the primary volume 206 falls. At this stage, the oil 401 is cold and relatively viscous, and the flow through the first wall 211 and second wall 212 is limited to a relatively low rate of flow compared to the rate at which oil 401 is pumped from the primary volume 206. Oil 401 pumped from the primary volume 206 lubricates the engine 102 but eventually falls back down towards the sump 103A, where at least a portion of the returning oil passes through the slots 1408 and lands on the first cover wall 1904.

[0158] At this stage, the returned oil 401 passes through the apertures of the mesh forming the first cover wall 1904 and begins to fill the secondary volume 207. When the secondary volume 207 is full and the level of oil 401 has reached the top of the high portion 1906 of the first cover wall 1904, which provides the second weir means 222, the oil overflows the second weir means 222 and falls onto the cover 1907. At this stage, the oil 401 falling on the cover 1907 passes through the holes in the mesh forming the cover 1907 and begins to fill the intermediate volume 208.

[0159] During filling of the secondary volume 207 and the intermediate volume 208 the relatively small second intermediate volume 1903 in the second wall 212 also fills with oil 401.

[0160] When the intermediate volume 208 is full and the level of oil 401 in the intermediate volume 208 has reached the top of the high portion 1910 of the cover 1907, which forms the first weir means 217, the oil overflows the first weir means 217 and returns to the primary volume 206. This situation is shown in FIG. 21.

[0161] In FIG. 21 the secondary volume 207 and the intermediate volume 208 are full of oil 401 and the level of oil in the primary volume 206 has dropped in comparison to the initial level shown in FIG. 20. From the moment when the oil 401 begins to overflow the first weir means 217, additional returned oil falling towards the first cover wall 1904 lands on oil residing above the first cover wall 1904 and overflows into the intermediate volume 208. The oil residing above the first cover wall 1904 may therefore warm up but the oil below the first cover wall 1904 is undisturbed and remains cold. The oil overflowing into the intermediate volume 208 flows over the cover 1907 and into the primary chamber 206, where it may be recirculated around the engine 102 via the pickup tube 1506.

[0162] As the engine 102 is run, the oil 401 circulated around the engine 102 and returned to the primary volume 206 is heated up by the engine 102, but the oil 401 in the secondary volume 207 and the intermediate volume 208 remains relatively stagnant and cool. Because only the relatively small volume of oil 401 in the primary volume 206 is being repeatedly circulated around the engine 103 at this stage, the oil 401 in the primary volume 206 reaches higher temperatures more quickly than it would do if all of the oil 401 were being circulated around the engine 103. Consequently, the viscosity of the oil 401 used to lubricate the engine 102 reduces more rapidly than it would if all of the oil 401 were being circulated, and so the efficiency of the engine 102 increases more rapidly.

[0163] Because the first weir means 217 and the second weir means 222 extend up to about the same height, the levels of oil 401 in the secondary volume 207 and the intermediate volume 208 are substantially equal, and there is no difference in pressure of the oil from one side of the second wall 212 to the other side. Consequently, there is no leakage of oil 401 from the secondary volume 207 to the intermediate volume 208 through the layers of mesh 1901 and 1902 forming the second wall 212.

[0164] When the intermediate volume 208 is first filled with oil 401, the oil in the intermediate volume 208 is relatively cold and has a high viscosity. Consequently, oil may leak through the first wall 211 but only slowly. Almost all oil 401 that flows over the second weir means 222 also flows over the first weir means 217 into the primary volume 206, but a smaller portion of the oil flowing over the second weir means 222 tops up the intermediate volume 208 to maintain its oil at the same level as that of the secondary volume 207.

[0165] While the oil sump 103A is in this state, if the engine 102 is temporarily stopped, for example for a minute at a traffic junction, oil will continue to leak slowly through the first wall 211 and as a result the level of oil in the intermediate volume 208 may begin to fall. A pressure difference will therefore be produced across the first layer 1901 of the second wall 212 and oil will begin to leak though the first layer 1901 as a result. This in turn will cause a pressure difference to appear across the second layer 1902 of the second wall 212 and oil will begin to leak from the secondary volume 207 into the second intermediate volume 1903 in the second wall 212. However, due to the high viscosity of the cold oil in the secondary volume 207 only a relatively slow rate of leakage results. It will also be appreciated that the pressure differences across each layer 1901 and 1902 of the second wall will be reduced when compared to a similar arrangement that has only one layer of mesh.

[0166] During operation of the engine 102, the temperature of oil in the intermediate volume 208 slowly rises due to conduction through the first wall 211 and also due to the small quantities of hot oil used to top up the intermediate volume 208. As its temperature rises, the viscosity of oil 401 in the intermediate volume 208 reduces and the rate of leakage of oil through the first wall 211 increases. Consequently, the portion of oil flowing over the second weir means 222 that is used to top up the intermediate volume 208 increases while the portion flowing over the first weir means 217 decreases.

[0167] The mesh forming the cover 1907 limits the rate at which oil 401 is able to flow into the first portion 1908 of the intermediate volume 208. When the rate of oil flowing through the first wall 211 becomes greater than the rate of oil flowing through the cover 1907, the level of oil 401 in the first portion 1908 of the intermediate volume 208 begins to drop. This causes a difference in pressure across the second wall 212 that causes the oil 401 to begin flowing from the secondary volume 207 through the second wall 212 into the intermediate volume 208. Oil in the secondary volume 207 is then topped-up with hot oil flowing through the mesh forming the first cover wall 1904.

[0168] When the rate of flow of oil 401 through the second wall 212 becomes greater than the rate at which oil is topping up the secondary volume 207, the level of oil 401 in the secondary volume 207 begins to drop. FIG. 22 shows the oil sump 103A at this stage, in which the level of oil 401 in the intermediate volume 208 has dropped and consequently the level of oil 401 in the secondary volume 207 has begun to drop. From this time onwards most of the oil 401 returned to the first cover wall 1904 falls through the mesh forming the first cover wall 1904 into the secondary volume 207, and oil 401 flows through the second wall 212 and the first wall 211 to the primary volume 206, where it is recirculated via the outlet 209. Thus, all of the oil 401 in the oil sump 103A is then used to lubricate the engine 102.

[0169] When the engine 102 is stopped for a prolonged period, oil 401 drains back down into the sump 103A and the levels of oil in the three volumes 206, 207 and 208 equalize, so that the sump 103A is once again in the state shown in FIG. 20.

[0170] In an alternative embodiment, the oil sump has a first wall surrounding a primary volume and a second wall surrounding the first wall, so that the intermediate volume surrounds the primary volume and the secondary volume surrounds the intermediate volume, in a similar manner to the oil sump 103 of FIGS. 15 to 22. However in the alternative embodiment, the sump is not provided with baffles 1421 and 1422 as described with reference to FIGS. 15 to 22.

[0171] Another alternative sump 103A, embodying the present invention is shown in the plan view of FIG. 23. The sump 103A of FIG. 23 is similar to that of FIGS. 15 to 22, except in the configuration of its baffles 1421 and by the absence of the baffles 1422 in the form of louvres surrounding the pickup chamber 206.

[0172] The sump 103A of FIG. 23 has four baffles 1421 which extend inwards from a respective first position 1502, next to the outer wall 204 of the sump 103A, to a respective second position 1503, next to a pickup chamber 206. A gap 2302 is provided between each baffle 1421 and an end 2303 of a neighbouring baffle 1421. Each of the gaps 2302 enable a flow of oil from a respective outer chamber 1501 to the pickup chamber 1504 alongside a baffle 1421 that extends past the gap 2302. For example, oil is able to flow from the outer chamber 1501D, through the gap 2302 between the baffle 1421D and the end 2303 of the baffle 1421A, and into the pickup chamber 1504 alongside the baffle 1421D. Each of the baffles 1421 has an end portion 2301 that extends from its second position 1503 around the pickup chamber 206, which causes oil entering the pickup chamber 206 to circulate within the pickup chamber 206 during use. In the present embodiment the end portions 2301 extend along a curve, but in an alternative embodiment the end portions are straight.

[0173] The end portions 2301 of the baffles 1421 all extend in the same rotational direction from the second positions 1503 around the pickup chamber 1504. In the present example, the end portions 2301 all extend clockwise around the pickup chamber 1504 to an end 2303 of the baffle 1421. Consequently, the baffles 1421 cause oil flowing into the pickup chamber 1504 from each of the outer chambers 1501 to flow in the same rotational direction (i.e. clockwise in this embodiment) around the pickup chamber 1504. In addition, air pumped through the sump 103A by bay-to-bay breathing, as described with reference to FIGS. 14 to 18, is caused to circulate in the same rotational direction (i.e. clockwise in this embodiment.)

[0174] The sump 103A of FIG. 23 has a first wall 211, a second wall 212, a first cover wall 1904 and a cover 1907 like those described above in regard to the sump 103A of FIGS. 15 to 22.

[0175] In the above described embodiments of FIGS. 15 to 23, the sump 103A comprises: four baffles 1421 that extend inwards from the outer wall 204 to the pickup chamber 206; and a corresponding number (i.e. four) outer chambers 1501. However, in some alternative embodiments the sump 103A comprises just three such baffles 1421, while in other embodiments the sump comprises more than four of such baffles 1421. For example, in one embodiment, in which the engine 102 has six cylinders, the sump has six baffles 1421 defining six outer regions.

[0176] Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

[0177] Features described in the preceding description may be used in combinations other than the combinations explicitly described.

[0178] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0179] Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

[0180] Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.