WO1999021637A1

WO1999021637A1 - Fluid filter, more particularly for hydraulic drive systems

Info

Publication number: WO1999021637A1
Application number: PCT/NL1998/000604
Authority: WO
Inventors: Paul Ernest Staff; Geurt Jan Hendrik Vleemingh
Original assignee: Fairey Arlon B.V.
Priority date: 1997-10-24
Filing date: 1998-10-21
Publication date: 1999-05-06
Also published as: NL1007358C2; AU9766198A

Abstract

A fluid filter having an inlet and an outlet with an annular cylindrical filter element therebetween. The filter element is of the radially outward flow type. It simultaneously functions as a by-pass valve. The outlet is adapted for connection to a fluid reservoir via an outwardly opening and inwardly biased relief valve and an inwardly opening and outwardly biased suction valve.

Description

Fluid filter, more particularly for hydraulic drive systems.

The invention relates to a fluid filter, comprising a housing with a radial flow type filter element of an annular cylindrical shape placed therein, said filter element dividing the space within the housing into a space outside and around the filter element and a separate space within the element; a head that closes said housing at one end and comprises an inlet chamber for the liquid to be filtrated and an outlet chamber for filtrated liquid, the inlet chamber being connected to the space on the inlet side of the filter element, whereas the space on the outlet side of the filter element is connected to the outlet chamber, and wherein a by-pass connection is provided between the inlet chamber and the outlet chamber which by-pass connection is normally closed by a by-pass valve, an outwardly opening and inwardly biased relief valve and an inwardly opening and outwardly biased suction valve being provided at the end of the housing opposite from said head, said valves being connected with the space on the outlet side of the filter element.

Such a filter is known from patent document DE-42 06 420.

Such a filter element is more particularly adapted for use in a situation, in which a hydraulic liquid flow from a main system is used to feed one or more consumers in an auxiliary system, such as the hydraulic feed pump for the hydromotors of the wheel drive of a mobile hydraulic device. In such a situation the filter is placed with its end, in which said relief valve and said suction valve are provided, onto or in a reservoir for hydraulic liquid, while the filter head is connected with its inlet chamber to a supply conduit for liquid to be filtrated and connected with its outlet chamber to one or more consumers to be supplied.

In normal use the hydraulic liquid is supplied in excess to the inlet chamber of the filter head, while the encountered back pressure on the inlet side of the filter element is low and the liquid is flowing through the filter element to the outlet space of the housing and from there via the outlet chamber in the filter head to the consumer (s) ; the excess liquid results in an increase of pressure within the outlet space of the filter housing which causes the relief valve to open, so that the excess liquid can flow to the reservoir. In case of a too high back pressure at the inlet of the filter, which may be an indication that the filter is blocked up, the by-pass valve opens to allow the liquid to flow directly to the consumer. Furthermore, in case the supply of liquid is unsufficient liquid may be sucked directly from the reservoir.

The present invention aims at providing an improved filter of the type indicated hereinabove. According to the invention this aim is achieved in that the annular cylindrical filter element is of a type, with which the liquid is flowing radially outwardly from the interior of the filter element, said filter element fulfilling also the function of a by-pass valve, for which purpose the open annular end of the filter element bears under pretension on a seat ring that is positioned within the connecting opening between the inlet chamber and the outlet chamber of the filter head.

This means that a separate by-pass valve is not required any longer.

Filter elements of the type, with which the fluid to be filtered is flowing radially outwardly from the interior of the element and with which one end of the filter element is closed by a disc-shaped bottom, are well-known per se and have the advantage, that the separated contaminants are collected within the space confined by the annular cylindrical filter element so that these contami- nants will not remain in the filter housing when changing the filter element. The latter point may be considered of particular importance for a filter of the type referred to hereinbefore, with which under special circumstances (a blocked-up filter element) unfiltrated liquid may flow to the consumer.

The use of a filter element of the radially outward flow type means, that the annular space around the filter element constitutes the outlet space of the housing. This enables the filter to be further improved, which improvement consists therein, that an auxiliary wall is positioned in the annular space between the filter element and the wall of the filter housing, said auxiliary wall dividing the annular outlet space within the housing into an inner section and an outer section and being carried out as an auxiliary or coarse filter along at least part of its length. In this way the filter according to the invention has the advantage, that also in case of a blocked-up filter element a (be it coarsely) filtrated liquid flow is supplied to the consumer(s) .

A preferred embodiment is characterized in that the lower part of the auxiliary wall is performed as a coarsely filtrating auxiliary filter element of the radially outward flow type, which is coaxially placed below the (main) filter element within the housing and has its lower annular end sealingly bearing on the bottom of the filter housing, wherein the relief valve and the suction valve are positioned in the space within the annular auxiliary filter element. This embodiment, in which the auxiliary wall extends from a location adjacent the upper end of the filter housing along a substantial part of the length of the filter housing in the form of a circumferentially closed shell, has the additional advantage, that when placing the filter on a tank, such that the housing beco- mes partially immerged in the liquid supply within the tank, the space around the shell will be always filled by oil, so that there is no risk for sucking air from the outlet chamber of the filter head.

A particular embodiment of the invention is characterized in that the auxiliary filter element is simultaneously functioning as a second suction valve and is there- fore mounted for a sliding movement within the shell- shaped auxiliary wall, so as to be lifted from the bottom of the filter housing functioning as a seat in case of a differential pressure that is larger than the differential pressure causing the first suction valve to open. This special embodiment secures that also in the very special case, wherein the auxiliary filter element is blocked up as well, liquid may be sucked from the reservoir.

The invention also relates to a hydraulic circuit, comprising a filter having an inlet for hydraulic fluid to be filtrated and an outlet for filtrated hydraulic liquid, said outlet having, on one hand, an outlet branch for connection to the inlet of an hydraulic consumer and, on the other hand, an outlet branch with an overflow valve connected to a hydraulic reservoir, wherein a by-pass conduit comprising a by-pass valve is provided parallel to said filter, said by-pass conduit being connected to said outlet at a location upstream from said outlet branch and wherein a suction valve is provided parallel to the overflow valve in the outlet branch towards the reservoir, as is disclosed in patent document DE 42 06 420.

The circuit according the present invention is characterized in that an auxiliary filter is provided in series with the said filter and at a location downstream of the outlet branch to the reservoir.

Further features of the invention will be hereinafter further explained by way of example with reference to the drawings. Fig. 1 shows a vertical cross-section, according to the plane I-I in fig. 2, of the filter according to the invention, in the normal use position; fig. 2 is a plan view of the filter of fig. 1; fig. 3, 4 and 5 show three positions of use, in which a liquid excess is discharged to the reservoir or (additional) liquid is sucked from the reservoir respectively and fig. 6 shows the hydraulic circuit of the filter of the present invention.

1 is a filter head, within which there are a substantially cylindrical inlet chamber 2 and an outlet chamber 3 positioned as an arc around the former. 2a is a pair of inlet connections for liquid to be filtrated, and 3a is a pair of outlet connections for filtrated liquid.

The inlet chamber 2 has its upper end closed by a cover 4 and its lower end connected with the outlet chamber 3. A seat ring 5 is provided in the (reduced) connec- ting area between the inlet chamber 2 and the outlet chamber 3 and is held in place by the cover 4 via a bridge piece 6 and a spring 7. The head 1 has a laterally projecting mounting flange 8, by means of which the head may be mounted onto a reservoir for (hydraulic) liquid. The head also has a downwardly projecting connecting sleeve 9 in alignment with the cylindrical wall of the inlet chamber 2.

10 is a substantially cylindrical filter housing, which is formed e.g. of sheet material and the upper end portion of which sealingly engages the connecting sleeve 9. Within the housing 10 there is provided an annular cylindrical filter element 11; liquid may flow radially outwardly from the interior of said filter element. For that purpose the space 12 within the filter element is connected through the upper end of the filter element with the inlet chamber 2, whereas the lower end of the filter element is closed by a bottom 13. The filter element 11 is pressed with its annular upper end onto the seat ring 5. The required pressure is delivered by a pressure spring 14 on the lower end portion of a central support rod 15 that extends from the bridge piece 2 downwardly and sealingly projects through the bottom 13. The spring 14 is e.g. sized such, that the filter element 11 will be lifted from the seat ring 5 as soon as the pressure within the inlet chamber 2 and the space 12 exceeds a value of e.g. 2 bar.

An auxiliary jacket 16 is provided in the annular space between the filter element 11 and the circumferential wall of the filter housing 10. The auxiliary jacket 16 is clamped with its upper end portion between the seat ring 5 and the wall of the inlet chamber 2 and extends downwardly beyond the lower end of the filter element 11. An annular cylindrical auxiliary filter element 17 is positioned in coaxial relationship to the main filter element 11 and placed in the lower part of the housing 10; like the main filter element 11 the auxiliary filter element is adapted to have liquid flow radially outwardly from its interior. However, the filtering effect of the auxiliary filter element 17 is substantially coarser than that of the main filter element 11 and thus has a length, which is a fraction only of that of the main filter element 11. A sealing lip 17c is provided on the upper end portion 17a of the auxiliary filter element 17, by means of which the auxiliary filter element 17 sealingly and slidingly projects into the lower end portion of the auxiliary jacket 16, whereas the auxiliary element 17 sealingly bears with its lower edge portion 17b onto the bottom 19 of the housing 10 which bottom is provided with a central opening 18. For this purpose the upper and lower end portions 17a and 17b are provided or covered with a suitable sealing material.

The auxiliary filter element 17 has its lower end portion 17b attached to a seat ring 20 positioned within the cross-sectional area of the opening 18. The seat ring 20 is provided with a bridge piece 21. A pressure spring 22 acts upon the bridge piece 21 and bears onto the support rod 15. By means of the pressure spring 22 the auxi- liary filter element 17 is pressed with its lower end 17b onto the bottom 19.

The bridge piece 21 is also provided with a downward- ly extending central rod 23, carrying a saucer-like element 24 at its lower end. A helical spring 25 bears onto said saucer-like element. A ring-shaped valve body 26 cooperates with the seat ring 20 and supports on the upper end of the helical spring 25. The inner circumferential edge of the valve body 26 constitutes a seat for a valve body 28 that is slidably mounted onto the rod 23 and is downwardly biased by a spring 27.

The valve body 26 constitutes, in combination with the valve body 28, a relief valve which is spring loaded by the spring 25 in the upward direction and is adapted to be opened downwardly against the action of said spring, whereas the valve body 28 is adapted to function separately as an upwardly opening suction valve against the action of the spring 27 while valve body 26 is closed.

The operation of the above described filter will now be described also with reference to the condition of use shown in fig. 3, 4 and 5.

During normal use the (clean) main filter element 11 bears with its ring-shaped upper end sealingly onto the seat ring 5. The liquid entering at 2a flows from the space 12 in radial direction through the filter element 11 into the space between the filter element 11 and the auxiliary jacket 16. From there the liquid flows via the radially outwardly flow type auxiliary filter element 17 into the space outside the auxiliary jacket 16 and into the outlet chamber 3 connected therewith for suction therefrom by a pump feeding a consumer device. A certain overpressure builds up downstream of the filter element 11. As soon as this overpressure exceeds a certain value of e.g. 0.5 bar, this is an indication that the need for (hydraulic) liquid is less than the supply, due to which the closing force of the spring 24 is overcome, so that the relief valve 26, 28 will open and the excess liquid may flow to the reservoir. This condition of use is shown in fig. 3. When, however, on any moment there is an underpressure of e.g. 0.03 bar this means that the need for hydraulic liquid is larger than the offer. In that case valve 28 will open against the action of the closing spring 27 so that the shortage of hydraulic liquid is sucked from the reservoir. This condition of use is shown in fig. 1.

Fig. 5 shows the condition of use at the starting up of the hydraulic system, when the hydraulic fluid is still cold and thick and atmospheric pressure prevails within both the filter housing and the liquid reservoir, while the pump (not shown) feeding the consumer device "demands" liquid. This demand results in an underpressure within the outlet space 3 and therefore within the space around the auxiliary jacket 16 connected therewith as well as in the filter element 17. This underpressure results in an up- wardly directed force on the filter element 17 which will, in case of an underpressure value of e.g. 0.15 bar, overcome the closing force of the spring 22. In that case the filter element 17 is lifted from the bottom 19, so that liquid may flow from the reservoir through the opening 18 into the filter housing.

Finally fig. 6 shows the hydraulic circuit, which is integrated in the filter of fig. 1. In this circuit adapted symbols are used to designate the filter element 11 and the auxiliary filter element 17. For the rest the circuit speaks for itself.

Claims

C L A I M S

1. A liquid filter, comprising a housing (10) with a radial flow type filter element

(11) of an annular cylindrical shape placed therein, said filter element (11) dividing the space within the housing

(10) into a space outside and around the filter element

(11) and a separate space (12) within the element; a head (1) that closes said housing (10) at one end and comprises an inlet chamber (2) for the liquid to be filtrated and an outlet chamber (3) for filtrated liquid, the inlet chamber (2) being connected to the space (12) on the inlet side of the filter element (11) , whereas the space on the outlet side of the filter element is connected to the outlet chamber (3) , and wherein a by-pass connection is provided between the inlet chamber (2) and the outlet chamber (3) which by-pass connection is normally closed by a by-pass valve (11) , an outwardly opening and inwardly biased relief valve (26, 28) and an inwardly opening and outwardly biased suction valve (28) being provided at the end (19) of the housing (10) opposite from said head (11) , said valves (26, 28; 28) being connected with the space on the outlet side of the filter element (11) , characterized in that the annular cylindrical filter element (11) is of a type, with which the liquid is flowing radially outwardly from the interior

(12) of the filter element, said filter element (11) fulfilling also the function of a by-pass valve, for which purpose the open annular end of the filter element (11) bears under pretension on a seat ring (5) that is positio- ned within the connecting opening between the inlet chamber (2) and the outlet chamber (3) of the filter head (1) .

2. A fluid filter according to claim 1, characterized in that in the annular space between the filter element (11) and the wall of the filter housing (10) an auxiliary wall (16) is positioned, said auxiliary wall (16) dividing the annular outlet space within the housing (10) into an inner section and an outer section and being carried out as an auxiliary or coarse filter (17) along at least part of its length.

3. A fluid filter according to claim 2, characterized in that the lower part of the auxiliary wall (16) is perfor- med as a coarsely filtrating auxiliary filter element (17) of the radially outward flow type, which is coaxially placed below the (main) filter element (10) within the housing and has its lower annular end sealingly bearing on the bottom (19) of the filter housing (10) , wherein the relief valve (26, 28) and the suction valve (28) are positioned in the space within the annular auxiliary filter element (17) .

4. A fluid filter according to claim 3, characterized in that the auxiliary filter element (17) is simultaneously functioning as a second suction valve and is therefore mounted for a sliding movement within the shell-shaped auxiliary wall (16) , so as to be lifted from the bottom (19) of the filter housing (10) functioning as a seat in case of a differential pressure that is larger than the differential pressure causing the first suction valve (28) to open.

5. A fluid filter according to claim 4, characterized in that the auxiliary filter element (17) is attached with its lower ring-shaped edge (17b) to said seat ring (20) operating with said relief valve (26, 28) and is biased in the downward direction together with said seat ring (20) .

6. A fluid filter according to claim 5, characterized in that said seat ring (20) is provided with a bridge piece (21) , which is acted upon by a pressure spring (22) , that supports on the support (15) for the (main) filter element (11).

7. A hydraulic circuit, comprising a filter having an inlet for hydraulic fluid to be filtrated and an outlet for filtrated hydraulic liquid, said outlet having, on one hand, an outlet branch for connection to the inlet of an hydraulic consumer and, on the other hand, an outlet branch with an overflow valve connected to a hydraulic reservoir, wherein a by-pass conduit comprising a by-pass valve is provided parallel to said filter, said by-pass conduit being connected to said outlet at a location upstream from said outlet branch and wherein a suction valve is provided parallel to the overflow valve in the outlet branch towards the reservoir, characterized in that an auxiliary filter is provided in series with the said filter and at a location downstream of the outlet branch to the reservoir.

8. A hydraulic circuit according to claim 1, characterized in that the inlet side has a connection to the reservoir, in which connection an auxiliary suction valve is provided.