FORM 2
THE PATENT ACT 1970 (39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See Section 10, and rule 13)
1. TITLE OF INVENTION
OIL RESERVOIR COMPRISING AN OIL FILTER
2. APPLICANT(S)
a) Name : ZF FRIEDRICHSHAFEN AG
b) Nationality : GERMAN Company
c) Address : 88038 FRIEDRICHSHAFEN,
GERMANY
AND
a) Name : ROBERT BOSCH GMBH
b) Nationality : GERMAN Company
c) Address : 70469 STUTTGART,
GERMANY
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed: -

The invention relates to an oil reservoir for a hydraulic system, comprising reservoir housing and an oil filter integrated in the reservoir housing, the reservoir housing preferably being composed of plastic.
Oil reservoirs serve, for example in automotive engineering, for storing the oil, conveyed in a circuit via the reservoir, of a hydrostatic fan system for cooling the engine. According to the prior art, such oil reservoirs are often not equipped with an oil filter. Since, however, it is essential to filter out abraded material or any impurities from the oil in order to protect the components of a hydraulic system, it is necessary, when using an oil reservoir without integrated oil filter, to arrange a corresponding oil filter at another place in the system.
However, oil reservoirs with an integrated oil filter arranged inside the oil reservoir have also already been disclosed. Such an oil reservoir is described, for example, by DE 199 25 635 Al. In the case of the oil reservoir described in the document, the oil filter accommodated in the oil reservoir is additionally encapsulated in separate filter housing inside the oil reservoir housing. The special construction enables the oil filter to be arranged completely below the oil level irrespective of the filling level otherwise existing in the oil reservoir, so that during the filtering process the oil cannot take up any air which may lead to impairment of the operability of the cooling system and thus possibly to failure of assemblies of the motor vehicle. Although an oil reservoir designed in accordance with the document obviates the need for the separate arrangement of an oil filter in the hydraulic system outside the oil reservoir and, moreover, effectively prevents impairments of the system by air contained in the oil, the solution is relatively complex with regard to the encapsulation, required therefore, of the oil filter inside the oil reservoir.
Another possibility of avoiding impairment of the cooling system by air contained in the oil in the form of air bubbles consists in arranging, in the oil reservoir, guiding devices for directed oil guidance. By means of such guiding devices, the otherwise relatively short path between the oil inlet connecting piece and the oil outlet

Connecting piece(s) is extended, so that separation of any air contained in the oil is promoted on this longer path, the effectiveness of this measure being decisively determined, moreover, by the geometry of the guiding devices and of the guiding path provided by them for the oil. In this regard, cyclone systems in particular have proved successful for the separation of the air, such as, for example, those described by EP 1 669 119 Al and US 6,348,087 Bl. By means of such cyclone systems, the oil with any air bubbles contained therein is set into a rotational movement on a circular path and as a result the air is separated from the oil owing to the centrifugal force occurring during this and the different densities of hydraulic oil and air. Although in this connection EP 1 669119 Al in particular also relates to the formation of a corresponding cyclone arrangement inside or as part of an oil reservoir, the oil reservoir according to the document is a reservoir without integrated oil filter. The solution known from the US document is likewise obviously not provided, when used inside an oil reservoir, for a combination with an oil filter.
The object of the invention is to provide an oil reservoir which has an oil filter and with which, despite a simple construction, the passage, with the oil sucked in from the reservoir, of air bubbles into the circuit of a hydraulic system is avoided. The object is achieved by an oil reservoir having the features of the main claim. Advantageous embodiments and developments of the invention are provided by the subclaims.
The oil reservoir for a hydraulic system proposed to achieve the object comprises a reservoir housing having a housing bottom part and a reservoir top cover, materially or positively connected to the housing bottom part, and comprises an oil filter arranged in the reservoir housing. There is formed on the reservoir housing, which is preferably composed of plastic, an oil inlet connecting piece and at least one oil outlet connecting piece for connecting the oil reservoir to at least one oil circuit or a circuit of a hydraulic system, the oil stored by the oil reservoir, when the latter is incorporated into a corresponding hydraulic circuit, being sucked out of the

reservoir by means of an oil pump. Furthermore, an oil filler neck closable by means of a cap is provided on the oil reservoir.
According to the invention, there is further arranged in the reservoir housing at least one guiding element which is fastened to at least one inner wall of the reservoir housing and which forms a circular guiding path for the oil. By passing through this circular guiding path, the oil, after flowing through the oil filter and before leaving the oil reservoir via the oil outlet connecting piece (s), is forced into a rotational movement to separate any air contained in it. Owing to the centrifugal force thereby acting on the oil with any air included, the air is separated from the oil and can leave the oil reservoir via an air outlet opening arranged in the wall of the reservoir top cover or in the cap of the oil filler neck.
The oil reservoir according to the invention accordingly has an integrated oil filter which, however, does not have to be separately encapsulated, owing to the guiding path formed for the oil in the reservoir and the possibility provided thereby of effectively separating any air present in the oil. As a result, a simple construction for the oil reservoir is achieved, which nevertheless simultaneously acts as an oil filter and at the same time also takes account of the requirement to prevent the entrainment of air, in the form of air bubbles contained in the oil, into the hydraulic circuit.
According to a preferred embodiment of the invention, the guiding element(s) is(are) arranged around the oil filter. A hollow-cylindrical space surrounding the preferably cylindrical oil filter is formed by the guiding element(s). The inner walls of this hollow-cylindrical space form the circular guiding path, opening in this case in the direction of the at least one oil outlet connecting piece, for the oil. This embodiment is advantageously developed in that the circular guiding path is guided around the oil filter in more than one complete revolution in a spiral-shaped course. As a result, a long guiding path is formed and a strong turbulence of the oil, advantageous with regard to the separation of the air, is achieved.

In a particularly advantageous embodiment of the oil reservoir according to the invention, the oil filter is equipped with a filter safety valve. By this filter safety valve, the oil filter is protected from destruction by any occurring pressure spikes of the oil entering the oil reservoir from the oil circuit via the oil inlet connecting piece and supplied to the oil filter. For this purpose, a bypass is opened by the filter safety valve when corresponding pressure spikes occur, via which bypass some of the oil passes into the guiding path and via the latter to the oil outlet connecting piece (s) without passing through the oil filter. In this regard, it is acceptable, in order to protect the oil filter from destruction, that a small part of the oil passes unfiltered back into the circuit in the rare instances of sporadic pressure spikes.
In accordance with a practical embodiment having a cylindrical reservoir housing, the oil inlet connecting piece and the at least one oil outlet connecting piece are formed on the reservoir bottom of the oil reservoir. In this case, the oil inlet connecting piece, arranged centrally on the reservoir bottom, opens directly into the oil filter, which is formed as a hollow cylinder, projects vertically from the inside of the reservoir bottom and is closed at its top side. The oil outlet connecting piece(s) are arranged laterally beside the oil filter and outside the hollow-cylindrical space surrounding the latter and formed by the at least one guiding element fastened to the reservoir bottom. This embodiment described can be further developed in that a baffle plate is arranged in the reservoir housing above the hollow-cylindrical space. This baffle plate prevents the oil forced into a rotational movement from moving upwards in the outer reservoir regions and a funnel-shaped vortex being formed in the oil filter, which would reduce the amount of oil passing through the filter in each case. Preferably, in this case, the housing bottom part and the housing top cover are connected to one another by a welded connection, by means of which the baffle plate extending horizontally between the housing bottom part and the housing top cover is also fastened to the reservoir housing.
In the above-described embodiment having the oil filter projecting vertically from the housing bottom and the oil inlet connecting piece opening into the oil filter, a

filter safety valve is realised in accordance with a preferred development in that the oil filter is spring-mounted in the oil reservoir. For this purpose, in a corresponding embodiment, the oil filter is spring-mounted, on a bar arranged to form an abutment in the oil filler neck, via a tappet arranged at its top side, a shoulder formed on the tappet and a helical spring resting on the shoulder. The oil filter is pressed upwards owing to its spring-mounting in the event of an excess pressure of the oil flowing into the filter, so that some of the oil can flow unfiltered beneath the oil filter, along the outside of the oil inlet connecting piece projecting into the oil filter, into the oil reservoir.
One possible embodiment of the oil reservoir according to the invention, which is designed for incorporation into hydraulic circuits of a motor vehicle, has two oil outlet connecting pieces and is at the same time part of two independent hydraulic circuits. Such an oil reservoir could possibly be both part of a hydrostatic fan circuit and part of steering hydraulics in a motor vehicle. Furthermore, an additional inlet connecting piece for the entry of leakage oil collecting at the working assemblies of a hydraulic system and returned to the oil reservoir can also be provided on the oil reservoir according to the invention.
The invention will be described and explained again in detail with reference to an exemplary embodiment. In the associated drawings:
Fig. 1: shows one possible embodiment of the oil reservoir according to the invention in a three-dimensional representation with a section taken
axially;
Fig. 2: shows the oil reservoir according to Fig. 1 in plan view and without the reservoir top cover.
One possible embodiment of the oil reservoir according to the invention is shown in Fig. 1. The illustration shows the three-dimensionally represented oil reservoir in an

axial section, i.e. in a representation with a section taken longitudinally through the reservoir or parallel to the longitidina axis, 21.
The oil container consists essentially of the reservoir housing 1 and the oil filter 2 arranged therein, the reservoir housing 1 being formed by a housing bottom part 3 and a housing top cover 4 connected to the housing bottom part 3 by a welded connection. At the bottom 5 of the housing bottom part, the reservoir 3 has connecting pieces 6, 7, 18, namely an oil inlet connecting piece 6, an oil outlet connecting piece 7 and an additional inlet connecting piece 18 for leakage oil. The oil reservoir is connected to a hydraulic system (not shown in the figure) via the oil inlet connecting piece 6 and the oil outlet connecting piece 7 and is thus a constituent part of an oil circuit. The hydraulic oil which is returned from the hydraulic system enters the oil reservoir 'via the oil inlet connecting piece 6 and after it has been filtered is sucked back out of the oil reservoir into the circuit again via the oil outlet connecting piece 7 by a hydraulic pump (not shown).
The oil inlet connecting piece 6 opens, as can be seen from the figure, directly into the hollow-cylindrical oil filter 2 seated on the end of the oil inlet connecting piece 6. The oil filter 2, the construction of which is known from the prior art and which will therefore not be explained in detail here, filters abraded material and impurities coming from the system out of the oil, before the purified oil finally reaches the oil outlet connecting piece 7. According to the invention, a guiding element 10 is arranged around the oil filter 2, by which element oil exiting the oil filter 2 after filtering is guided on a circular guiding path 11 and thus forced into a rotational movement. The guiding element 10 prevents oil with any air bubbles included therein from passing on a direct path to the oil outlet connecting piece 7 and thus into the following hydraulic system. This simple measure helps to separate from the oil, if necessary, any air present in the oil on the longer path to the oil outlet connecting piece. Through the special shaping of the guiding element 10, which forms around the oil filter 2 a hollow-cylindrical space 12 which the oil, after passing through the oil filter 2, first enters on its path to the oil outlet connecting piece 7, the

oil as already stated, is set into a rotational movement. Owing to the centrifugal force acting during this on the oil and any air contained, the air, which has a lower density than the oil, is separated during the movement of the oil and air mixture along the circular guiding path 11 formed by the guiding element 10. The separated air can exit the oil reservoir via an air outlet opening (not visible in the representation) in the region of the oil filler neck 8 or the cap 9 closing the latter.
As is further evident from the figure, in the exemplary embodiment shown, a horizontally extending baffle plate 17 is arranged between the housing bottom part 3 and the reservoir top cover 4, which plate is welded together with the housing bottom part 3 and the reservoir top cover 4 at the edge of the oil reservoir. This baffle plate 17 prevents the oil set into a rotational movement from moving upwards in the outer region of the. oil reservoir and in the centre thereof,, ie, in. the region, of the oil filter 2, forming a downwardly directed vortex. Such a vortex would be undesirable because the capacity of the oil filter would thereby not be properly utilised.
In the represented exemplary embodiment of the oil reservoir according to the invention, the oil filter 2 is additionally equipped with a filter protection valve 13,14, 15. This valve is realised by the oil filter 2 being supported, via the tappet 13 arranged at its closed top side and a spring 15 resting on a shoulder 14 of this tappet, on a bar 16 arranged in the oil filler neck 8. If oil at too high a pressure passes into the oil filter 2 via the oil inlet connecting piece 6, the spring-mounted oil filter 2 is pressed upwards against the spring force of the spring 15, so that beneath the oil filter a kind of bypass is freed for the oil, via which some of the oil can flow along the outside of the oil inlet connecting piece 6, beneath the oil filter 2 into the oil reservoir. In this way, the oil filter 2 is protected from destruction by temporarily occurring excess pressures. Such excess pressures may arise, for example, if the oil reservoir is incorporated into a hydraulic system having an assembly, at first cold on start-up, in the oil which is then still relatively firm or viscous. The further inlet connecting piece 18 additionally arranged on the reservoir housing 1 serves for

returning, to the oil reservoir, leakage oil which escapes at assemblies of the hydraulic system.
Fig. 2 shows the oil reservoir according to Fig. 1 again, in a plan view, the reservoir top cover 4 and the baffle plate 17 having been removed. Here, the hollow-cylindrical space 12 formed by the guiding element 10 and the course of the guiding path 11 for the oil can be seen particularly clearly. It is evident that the oil is guided around the oil filter 2 in a circular movement, the oil moving in more than one revolution around the oil filter 2 owing to the spiral-shaped course of the guiding path 11. As can be seen, the guiding path 11 runs out in the vicinity of the oil outlet connecting piece 7. The oil freed from the air owing to the centrifugal force passes finally back into the hydraulic system again via the oil outlet connecting piece 7. On the outer wall, the oil reservoir has a fastening plate 19, by means of which it can be fastened, via holes 20 made therein, in the engine compartment of a motor vehicle.

List of reference symbols
1 reservoir housing
2 oil filter
3 housing bottom part
4 housing top cover
5 housing bottom
6 oil inlet connecting piece
7 oil outlet connecting piece
8 oil filler neck
9 cap

10 guiding element
11 guiding path
12 hollow-cylindrical space
13 tappet
14 shoulder
15 spring
16 bar
17 baffle plate
18 inlet connecting piece
19 fastening plate
20 hole
21 longitudinal axis

WE CLAIM:
1. Oil reservoir for a hydraulic system, comprising a reservoir housing (1)
having a housing bottom part (3) and a reservoir top cover (4), materially or
positively connected to the housing bottom part (3), and comprising an oil
filter (2) arranged in the reservoir housing (l), there being formed on the
reservoir housing (1) an oil inlet connecting pie£e (6) and at least one oil outlet
connecting piece (7) for connecting the oil reservoir to at least one circuit of a
hydraulic system, and an oil filler neck (8) closable by means of a cap (9),
characterised in that there is arranged in the reservoir housing (1), fastened to
at least one inner wall of the reservoir housing (1), at least one guiding
element (10) which forms a circular guiding path (11) for the oil, by which the oil, after passing through the oil filter (2) and before leaving the oil reservoir via the oil outlet connecting piece(s) (7), is forced into a rotational movement to separate air contained in it, the separated air leaving the oil reservoir via an air outlet opening arranged in the wall of the reservoir top cover (4) or in the cap (9) of the oil filler neck (8).
2. Oil reservoir according to Claim 1, characterised in that the guiding element(s) (10) is(are) arranged around the oil filter (2).
3. Oil reservoir according to Claim 2, characterised in that a hollow-cylindrical space (12) surrounding the cylindrical oil filtef (2) is formed by the guiding elements) (10) the inner waYis or which space forrn tne circular guiding path (11) opening in the direction of the at least one oil outlet connecting piece (7).
4. Oil reservoir according to Claim 3, characterised in that the circular guiding path (11) is guided around the oil filter (2) in more than one complete revolution in a spiral-shaped course.

5. Oil reservoir according to one of Claims 1 to 4, characterised in that the oil filter (2) is equipped with a filter safety valve (13, 14, 15), by which the oil filter (2) is protected from destruction by pressure spikes of the oil entering the oil reservoir from the oil circuit via the oil inlet connecting piece (6) by the filter safety valve (13, 14, 15) opening a bypass when such pressure spikes occur, via which bypass some of the oil passes to the oil outlet connecting piece(s) (7) without passing through the oil filter (2) via the guiding path (11).
6. Oil reservoir according to one of Claims 3 to 5 having a cylindrical reservoir housing (1), characterised in that the oil inlet connecting piece (6) and the at least one oil outlet connecting piece (7) are formed on the reservoir bottom (5) of the oil reservoir, the oil inlet connecting piece (6), arranged centrally on the reservoir bottom (5), opening directly into the oil filter (2), which is formed as a hollow cylinder, projects vertically from the inside of the reservoir bottom (5) and is closed at its top side, and the at least one oil outlet connecting piece (7) being arranged laterally beside the oil filter (2) and outside the hollow-cylindrical space (12) surrounding the latter and formed by the at least one guiding element (10) fastened to the reservoir bottom.
7. Oil reservoir according to Claim 6, characterised in that a baffle plate (17) is arranged above the hollow-cylindrical space (12).
8. Oil reservoir according to Claim 7, characterised in that the housing bottom part (3) and the housing top cover (4) are connected to one another by a welded connection, by means of which the baffle plate (17) extending horizontally between the housing bottom part (3) and the housing top cover (4) is also fastened to the reservoir housing (1).
9. Oil reservoir according to one of Claims 6 to 8 having a filter safety valve (13, 14,15), characterised in that the filter safety valve (13,14,15) is realised by a spring-mounting of the oil filter (2) by the latter being spring-mounted, on a

bar (16) arranged to form an abutment in the oil filler neck (8), via a tappet (13) arranged at its top side, a shoulder (14) formed on the tappet (13) and a helical spring (15) resting on the shoulder, and by the oil filter (2) being pressed upwards owing to the spring-mounting in the event of an excess pressure of the oil flowing into the oil filter (2), so that some of the oil can flow unfiltered beneath the oil filter (2), along the outside of the oil inlet connecting piece (6) projecting into the oil filter (2), into the oil reservoir.
10. Oil reservoir according to one of Claims 1 to 9 for incorporation into hydraulic circuits of a motor vehicle, characterised in that this oil reservoir has two oil outlet connecting pieces (7) and is thus part of two separate hydraulic circuits.
11. Oil reservoir according to one of Claims 1 to 10, characterised in that this oil reservoir has an inlet connecting piece (18) for the entry of leakage oil collecting at the working assemblies of a hydraulic system and returned to the oil reservoir.