Patent Publication Number: US-2010108444-A1

Title: Vehicle Sump

Description:
FIELD OF THE INVENTION 
     The present invention relates to a sump for use in a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     The term “sump” is used herein to refer to the lower part of any liquid filled casing in a motor vehicle. As examples, the casing may be an engine crankcase or it may be the housing of gearbox, a transfer box or a differential. In the example of a crankcase, the sump is often formed as separate cover, pan or tray that is bolted on to the engine block. In other examples, the casing may itself be of a clamshell construction whereupon the lower part of the casing may serve as the sump. 
     The liquid in the examples given above is the oil used for lubricating the mechanical components housed within the casing. The lubricant needs to be drained and replaced from time to time and for this reason sumps are normally fitted with a drainage plug at the lowest point where the oil can collect. 
     Conventionally, the drainage plug is screwed into an internally threaded boss that projects downwards from the outer surface of the sump. The sump is often a low point on the underside of the vehicle and the projecting drainage plug therefore reduces the vehicle ground clearance. 
     OBJECT OF THE INVENTION 
     The present invention seeks to provide a sump design that that provides a low drainage point on the sump while reducing the downwards projection of the drainage plug. 
     SUMMARY OF THE INVENTION 
     A sump has a drainage hole and an internally screw-threaded boss surrounding the drainage hole for receiving a drainage plug, characterised in that the boss projects upwards into the sump and has at least one circumferential discontinuity to allow liquid within the sump to flow out of the drainage hole after removal of the drainage plug. 
     Conveniently, each discontinuity is formed as a radial groove in the part of the boss projecting above the inner surface of the sump. 
     In the preferred embodiment of the invention, the sump is formed as a casting and the boss is formed integrally with the sump during the casting process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a plan view from above of a sump of the invention, and 
         FIG. 2  is a section along the line II-II in  FIG. 1  also showing the drainage plug. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
       FIG. 1  shows a plan view of sump  10 . The sump is in the shape of a generally rectangular pan with a retaining flange  12  surrounding its upper end. The retaining flange  12  has holes  14  for receiving bolts that secure the sump  10  to a casing, which may for example be an engine crankcase or a gearbox housing. A gasket or sealing compound is used between the flange  12  and the casing to form a sealed chamber which can retain oil for lubrication. The sump need not of course be rectangular and the bottom of the sump need not be flat. 
     To enable the oil to be drained and replaced, a drainage hole  16  is provided, which in normal use is closed off by a removable screw-threaded drainage plug. To minimise the oil and sludge that can remain in the sump when it is drained, the hole  16  is normally located at the lowest point in the sump at which oil can collect. 
     Conventionally, an internally screw-threaded socket in which the drainage plug engages is arranged below the mouth of the hole  16 . This however results in the plug projecting downwards and reducing the ground clearance of the vehicle. 
     In the present invention, the drainage plug screws into a boss  18  that projects upwards into the oil chamber of the sump. A continuous boss would however have the effect of raising the mouth of the drainage hole  16  and preventing the sump from being drained completely. To prevent this from happening, the boss  16  is rendered circumferentially discontinuous by three radial grooves  20  arranged at 120° to one another. As can be seen from the section of  FIG. 2 , which also shows the drainage plug  22  and its sealing washer  24 , the grooves  20  extend down as far as the upper surface of the sump  10  and therefore permit total drainage of the sump. The grooves need not necessarily reach down to this extent and in practice, as it is important to maintain a minimum wall thickness in the sump, it may be necessary to reach a compromise between the amount of oil retained in the sump and the extent to which the plug projects beneath the profile of the sump. 
     Because of the provision of the projecting boss  18  on the inside of the sump  10 , its outer surface can also be recessed as shown in  FIG. 2  to receive the head of the drainage plug  22  thereby avoiding the need for any projection from the underside of the sump. 
     The boss  18  of the illustrated preferred embodiment of the invention has a conically tapering side wall. This allows oil to flow more smoothly during drainage and avoids sharp corners in which sludge can collect. 
     The sump in the drawings is formed as a casting and this enables the boss  18  to be formed as an integral part of the sump during the casting process. This reduces manufacturing costs by avoiding the need to attach a separately formed component to the sump and also reducing the numbering of machining steps involved. 
     The drainage plug illustrated in  FIG. 2  is essentially a bolt with a sealing washer. It should be stressed however that the type of plug used and the manner in which it is sealed is not of fundamental importance to the present invention. Hence, in place of the sealing washer, it is alternatively possible to use an O-ring seal or a conical seat seal between the plug and the sump. Furthermore, in place of a hexagonal head, the plug may have a non-circular blind hole or recess to be gripped for example by a hex key (also known as an Allen key). In this case, a much flatter head may be used having only sufficient thickness to ensure that enough torque can be applied to the plug to establish a seal and prevent the plug from working loose.