In general, oil filters are employed in engines and transmissions to purify the oil used to lubricate the engine or transmission. Originally, oil filtration in an engine or transmission has been effected using filters arranged separately outside and inside the oil pan. In general, the filter medium required for filtra- tion is arranged in the filter housing in various ways. The space available in an engine/transmission compartment is highly limited and as a result, the ten- dency recently has been to avoid bulky constructions in new developments of engines and transmissions and to optimize space economy by integration.

As a result, oil filters are now being used which are integrated in the oil pan of engines or transmissions. This allows rational utilization of the space available in the oil pan, because the latter is intended to receive oil not being used in the engine or transmission circulation. Such arrangements of oil filter inserts in an oil pan have been described in DE A1 197 35 444. 0, for example.

For trouble-free function of the oil filter in the oil pan, it is indispensable that tightness of the joint between filter unit and oil pan is constantly ensured even over ranges of high temperature and stress. One should keep in mind that the temperatures in the motor vehicle may range between-40 and +160°C, de- pending on the user's geographic location and temperature of the oil. As a re- sult of such massive stress caused by temperature, the filter unit frequently undergoes deformation after being used for some time. Regardless of tight- ness, this may give rise to problems with the functionality of the filter unit, es- pecially with respect to a possibly impaired joint between oil filter and engine or transmission.

In particular, the use of different materials for oil pan and filter insert, e. g. metal for oil pans and plastic for filter inserts, frequently gives rise to problems during assembly as a result of the dissimilar physical properties of these mate- rials, particularly problems with respect to tightness. Due to the long cure

times of the adhesive, bonding of the two half-shells of the oil pan required to date delays delivery of the complete oil filter system as would be preferred by the customer.

In particular, efforts are now being made to reduce the overall height of the oil filter units so as to allow an oil filter intake position as low as possible. How- ever, this implies significantly increased constructional requirements.

The technical object of the present invention was therefore to provide an oil pan for engines or transmissions having the oil filter unit integrated therein, which oil pan avoids the above-mentioned drawbacks, specifically enabling long-term and trouble-free oil filtration, and also has sufficient and permanent tightness even under major temperature fluctuations.

The above technical object is accomplished by means of an oil pan having an integrated oil filter unit, wherein part of the oil pan forms the bottom of the oil filter unit in such a way that the oil filter unit is fastened on the oil pan at least by means of an adhesive component and one or more punch rivets.

In a preferred embodiment, a sealing element is situated between oil filter unit and oil pan.

The construction can be of such a design that either a seal merely is inserted or contact-extruded, followed by riveting, or, an adhesive is applied instead of the seal, assuming the function of the seal and simultaneously joining the components.

Both the oil pan and filter unit can be made of any conceivable material suit- able in punch riveting. These materials include metallic or non-metallic materi- als or composite materials, such as metals, alloys, steels, or plastics which, in addition, can be coated with inorganic or organic substances. In a preferred embodiment, an oil pan made of metal, particularly sheet metal, die-cast alu- minum, or steel, and a filter unit made of plastic are used.

The actual filter unit comprises one or more filter media, such as segment screens, paper filters, as well as polyester filter felts which, depending on the material, can be disc-shaped or bag-shaped or folded, and a frame bordering

the filter medium, as well as a cover advantageously attached to the frame, which cover can be welded, for example. In a preferred fashion, the frame of the filter unit is formed by extruding around the filter medium.

In a preferred embodiment, the filter unit has a fastening area useful in fas- tening the filter unit to the oil pan. Said fastening area represents part of the filter unit frame, is of a design so as to extend-at least partially-parallel to the oil pan bottom, not unlike a foot, and advantageously has a groove on its underside which makes contact with the oil pan. The thus-designed frame of the filter unit allows fastening of the filter unit to the bottom of the oil pan by introducing an adhesive component in the groove described above. In addi- tion, the fastening area extending parallel to the bottom of the oil pan should be of a thickness so as to allow fitting of the oil pan with the aid of punch riv- ets.

Fastening of the filter unit within the oil pan is facilitated when the oil pan in the fastening area likewise has a groove which, in optimal fashion, is somewhat wider than the fastening area of the frame of the filter unit extending parallel to the bottom of the oil pan. This enables mating fixture of the filter unit on the bottom of the oil pan and prevents deformation of the filter unit after fixture as a result of drastic conditions of use.

A permanent and tight joint between frame and oil pan should be provided to permit trouble-free oil filtration. To this end, a seal element is preferably intro- duced in the groove situated in the fastening area of the frame of the filter unit.

The use of a seal simultaneously having adhesive properties was found to be particularly advantageous. Conventional materials, such as acrylate rubber (ACM), ethylene acrylate elastomer (AEM), or fluororubber (FPM), can be used as sealing element, while two-component or silicone adhesives represent examples of an adhesive sealing material.

Primarily due to the massive temperature fluctuations, fixture of the filter unit on the oil pan merely using seal and adhesive, as has been the case up to now, has resulted in leakages after some time and in deformation of sealant or adhesive and therefore, in the oil pan according to the invention, fixture of the frame on the oil pan is effected by means of joining using punch rivets, par- ticularly semi-tubular rivets.

Joining two or more joining parts using semi-tubular rivets has been known for some years and is already being used. In the automotive industry, for exam- ple, the aluminum body-in-white of motor vehicles meanwhile is worked using punch riveting. As has been described in DE 44 31 769 and DE 197 01 150, for example, punch riveting using semi-tubular rivets is based on the use of plastically deformable auxiliary joining parts and is characterized by indirect non-removable joining of two or more joining parts, especially sheet metal parts, without any prepunch operation, using an auxiliary joining part simula- neously functioning as clipping punch. The punch rivet designed as semi- tubular rivet, with a countersink bore designed as cutting edge, punches through the upper n-1 of n joining parts to undergo plastic deformation in the lowermost joining part by widening. The strength of the riveted joint particularly depends on the undercut SH achieved during widening.

This method is advantageous in that no preparatory works such as punching the joining parts are necessary, no deformation occurs-as contrasted by thermal processes, and that the lowermost joining part, not being punched through itself, represents a non-damaged protective layer and thus, a largely tight joint. Moreover, operation and maintenance costs for the punch rivet pro- cess are rated low.

Another benefit of this method can be seen in the potential of joining materials in an easy and liquid-tight fashion which are completely different in their physi- cal and surface properties. A device for performing the punch-riveting process has been described in the laid-open document DE 199 05 527, for example.

In an optimal fashion, punch riveting in the present oil pan according to the invention is used in the critical areas only, particularly in the corners, but is not basically limited with respect to the number of punch rivets used. The inventive combination of sealing element/adhesive and punch rivets achieves a perma- nent and tight joint between frame and oil pan with lowest-possible input and without the risk of filter unit deformation during use. In particular, by using a sealing adhesive, a significant reduction in the number of rivets is possible, with tightness being ensured at the same time. In this case, the rivets merely represent a fixture of the components during the drying phase of the adhesive and therefore, complete drying and curing of the adhesive prior to delivering to

the customer is no longer required. The oil pan therefore can be delivered to the customer directly after joining.

This not only enables system delivery, even within short terms, but also pur- poseful utilization of the space occupied during drying which to date has been used in the premises of the production site due to necessary drying prior to delivery.

Essentially, the material of the semi-tubular rivets to be used is determined by the hardness of the parts to be joined. It is preferred to use rivets made of stainless steel.

The present invention is also directed to a method of fastening an oil filter unit on an oil pan, said method comprising the following steps: - introducing a seal and an adhesive between the oil filter means and the oil pan; - joining the oil pan and the filter means, including the layer therebetween, by means of punch rivets.

In a preferred embodiment, the seal is introduced by inserting between the oil filter unit and the oil pan, the seal itself or the oil filter unit and/or oil pan addi- tionally being provided with an adhesive. Conventional substances such as one-or two-component silicone or polyurethane adhesives are used as adhe- sives. Common materials, such as those made of acrylate rubber (ACM), eth- ylene acrylate elastomers (AEM), or fluororubber (FPM) may find use as seals.

In another preferred embodiment, the seal initially is fixed on the filter unit and placed together with the latter on the oil pan. In a particularly preferred fash- ion, the seal is fixed by extrusion on the filter unit. Advantageously, materials e. g. those made of acrylate rubber (ACM), ethylene acrylate elastomers (AEM), or fluororubber (FPM) are used.

In a third preferred embodiment, the seal is introduced by injecting between filter unit and oil pan. To this end, it is advantageous to use sealing adhesives, such as silicone adhesives or two-component adhesives. It is convenient to

inject into the groove situated on the fastening area of the frame extending parallel to the oil pan. The oil pan of the invention will be described in detail with reference to the following figures which, however, are not intended to be limiting to the invention.

Fig. 1 shows the schematic arrangement of a preferred embodiment of the oil pan according to the invention in oblique top view. 1 represents the actual oil pan, simultaneously forming the bottom of the oil filter unit. The filter unit is comprised of frame 2 of the filter unit, which also has a fastening area 10 ex- tending at least partially parallel to the bottom of the oil pan, filter medium 9 and cover 3 of the filter unit. Frame 2 of the filter unit is formed by extruding around the filter medium 9. Conveniently, the cover 3 of the filter unit is welded on the frame 2 component during the production process.

The oil pan 1 preferably has a groove 8 corresponding in shape to the filter unit. Advantageously, the seal 4 which is situated between oil pan 1 and frame 2 of the filter unit is introduced in said groove 8. The adhesive component in- tended to fix frame 2 of the filter unit on the oil pan is omitted in this illustration.

Punch rivets 6 are used for additional fixture of the filter unit.

In regular operation, the oil passes from the engine or transmission circulation into the oil pan 1, flows through the inlet opening 7 into the interior of the filter unit beneath the filter medium 9, is drawn through filter medium 9 by means of a suction pump, and eventually passes back into the circulation via outlet opening 5. The outlet opening 5 is provided with a seal ring 11.

Fig. 2 illustrates a longitudinal section of the preferred embodiment of the oil pan according to the invention.

Fig. 3 shows an enlarged view taken from Fig. 2, which is a longitudinal sec- tion through fastening area 10 extending largely parallel to the oil pan 1. As elaborated therein, the oil pan 1 as well as the fastening area 10 of the filter unit have a groove 8, the shape of groove 8 of oil pan 1 being designed so as to enclose the fastening area 10 of the filter unit.

Fig. 4 corresponds to the section of Fig. 3, but unlike therein, the latter ex- tends through punch rivet 6. Fig. 4 sketches the joining site subsequent to

joining. The undercut formed during widening of the semi-tubular rivet in the course of the punch process is designated SH. Said undercut has an influence on the strength and tightness of the joint. As elaborated in Fig. 4, said joining comprises the oil pan 1, the fastening area 10 of the filter unit, as well as the seal 4.

Reference list 1 Oil pan 2 Frame of filter unit 3 Cover of filter unit 4 Seal or adhesive 5 Outlet opening 6 Rivet joint 7 Inlet opening 8 Groove 9 Filter medium 10 Fastening area of the filter unit frame 11 Seal ring