GB1568503A - Filter for liquids - Google Patents

Description

(54) A FILTER FOR LIQUIDS (71) We, ROBERT BOSCH GmbH, a German company of Postfach 50, 7000 Stuttgart 1, Germany., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the follow mg statement: The present invention is concerned with a filter for liquids and, more particularly, with a filter suitable for the filtration and cleaning of diesel fuel.

When diesel fuel is subjected to low temperatures, for example down to - 120 C.

the paraffin constituents of the fuel tend to precipitate and thus cause clogging and blockage of filters used for the cleaning of diesel fuel. With a view to solving this problem, a liquid filter has been proposed in which an annular filter insert is arranged concentrically with respect to a heating device. The heating device is constructed as a heat exchanger, the heating medium being hot air provided by the internal combustion engine with which the filter is associated.

The heat exchanger comprises a plurality of tubes through which the liquid, i.e. diesel fuel, is passed upstream of the filter insert.

This arrangement is necessarily relatively bulky so that the filter (containing within it the heat exchanger) is undesirably large and expensive and the efficiency of heat utilisation is undesirably low. Furthermore, there is little or no heating effect on start up of the engine with which the filter is associated.

We have now developed an improved filter for liquids. particularly diesel fuel. in which heating of the liquid is effected directly by the filter insert by using the latter as a resistance heating element. This filter can be relatively simply constructed and in a space-saving manner and it enables a liquid to be heated in the course of filtration with the most efficient use of energy.

According to the present invention, there is provided a filter for liquids, which comprises a housing having an inlet for liquid to be filtered and an outlet for filtered liquid and, within the housing, a filter insert consisting of a strip of electrical conductive filter paper spirally wound about an axial tube, the filter insert being arranged for axial flow of the liquid therethrough and being electrically connected to terminals on the housing so that the filter insert is adapted to constitute a resistance heating element.

In order that the invention may be more fullv understood a preferred embodiment thereof will now be described, by way of example. with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through a liquid filter.

Figures 2 and 3 show details, on a larger scale. of electrical connections to the filter insert of the filter shown in Figure 1, and Figure 4 is a side view of the contact clip shown in Figure 3.

Referring to Figure 1. a liquid filter 10 comprises a metal housing 11 consisting of a cup-like portion 12 and a cover 13. and, within the housing, an electrically nonconductive central tube 14, an apertured plate 16 engaging a shoulder 15 in the housing, and a filter insert 17 arranged between the inner wall of the housing 11, the central tube 14 and the apertured plate 16. Two unions 18, 19 are mounted on the cover 13. the centrally positioned union 18 serving as an outlet for filtered liquid and the other union. 19, serving as an inlet for liquid to be filtered. A positive terminal 21 is mounted on the cover 13. the contact pin 22 of the terminal passing into the interior of the housing through the cover 13 and being electrically insulated therefrom by a plastics sleeve 23.

The filter insert 17 consist of a strip 24 of filter material which is spirally wound around the central tube 14. The strip 24 has a conventional V-shaped cross section over its entire length and a sealing medium is resent between the free limbs of adjacent layers so that two spirally extending annular chambers are formed in the filter insert 17 open toward opposite ends. The ends 25, 26 of the strip 24 at the outer and inner periphery of the insert 17 are stuck to the adjacent layers. The strip 24 consists of a conventional filter paper which is made electrically conductive by the application of an appropriate coating thereto, which coating does not destroy its filtering properties.

As shown in Figure 1 and, on a larger scale, in Figure 2, a wire 27 leads from the contact pin 22 to a connector plate 28 which projects beyond one end surface of the filter insert 17 and which is rigidly connected to the outer end 25 of the strip 24 of filter material by means of a hollow rivet 29. As shown on a larger scale in Figure 3, a contact clip 31 engages the inner end 26 of the strip 24 of filter material, the lower end of the clip directly engaging the apertured plate 16 and thus producing an electrically conductive connection between the strip 24 and the apertured plate 16 and thus to the housing 11, which forms the negative terminal shown schematically at 32. The shape of the contact clip 31 can be seen in more detail in Figure 4. The filter insert 17 is sealed in the housing 11 by adhesive located at 33 and is separated from the inner wall of the cup-like portion 12 and from the apertured plate 16 by a cup-like insulating layer 34, the bottom portion of the layer 34 having openings 35 in the region of the apertured plate 16 so as to allow the filtered liquid to pass through. The terminals 21, 32 and the filter insert 17 thus form parts of an electrical heating device 36 in which the filter insert itself forms a heating resistance.

The method of operation of the liquid filter 10 is as follows, its function only being discussed insofar as is necessary for the understanding of the invention.

The diesel fuel to be cleaned flows through the inlet 19 into the housing 11, axially through the filter insert 17, upwards through the central tube 14 and out again through the outlet 18. If low temperatures prevail during operation, the paraffin tends to be precipitated out of the diesel fuel and to clog the pores of the strip 24 of filter material. The threshold of the ability to filter in respect of diesel fuel is established by DIN 51601; in accordance therewith, the temperature threshold for winter fuels at which the fuel must still be filterable, is - 120C. Such low temperatures can occur frequently with motor vehicles which left out of doors, that is not garaged. during winter. In order to facilitate filtration in these cases, a voltage is applied to the positive terminal 21 shortly before the engine is started, so that a current flows from the positive terminal 21, through the wire 27, the connector strip 28, from the end 25 to the end 26 of the strip 24 of filter material, through the contact clip 31, the apertured plate 16 and the housing 11 to the negative terminal 32. Heat is thus generated with the lowest possible electrical energy directly at the location at which it is also used, and the applied energy is used as efficiently as possible. Paraffin clogging the pores in the strip 24 of filter material is thereupon released and the diesel fuel can flow through the filter 17. It is a further advantage of this arrangement that it is only necessary to draw energy from the battery of the vehicle for a limited period.

Modifications may be made in the illustrated embodiment within the scope of the present invention. Thus, the construction of the filter and the arrangement of the electrical terminals may be varied.

WHAT WE CLAIM IS: 1. A filter for liquids, which comprises a housing having an inlet for liquid to be filtered and an outlet for filtered liquid and, within the housing, a filter insert consisting of a strip of electrical conductive filter paper spirally wound about an axial tube, the filter insert being arranged for axial flow of the liquid therethrough and being electrically connected to terminals on the housing so that the filter insert is adapted to constitute a resistance heating element.

2. A liquid filter according to claim 1, in which the housing is formed of metal, the axial tube of an electrically non-conductive material. the filter insert is separated from the housing by an electrically insulating layer and the inner and outer ends of the filter paper strip are electrically connected to the terminals.

3. A liquid filter according to claim 2, in which the housing comprises a cup portion and a cover and an apertured metal plate is located within the cup portion and serves to support the filter insert. and the outer end of the filter paper strip is electrically connected to a positive terminal mounted on the cover and inner end of the filter paper strip is electrically connected to the apertured metal plate, and thereby to the housing. through a contact clip.

4. A liquid filter according to claim 3, in which a connector strip is attached to the outer end of the filter paper strip by means of a hollow rivet.

5. A liquid filter substantially as herein

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. around the central tube 14. The strip 24 has a conventional V-shaped cross section over its entire length and a sealing medium is resent between the free limbs of adjacent layers so that two spirally extending annular chambers are formed in the filter insert 17 open toward opposite ends. The ends 25, 26 of the strip 24 at the outer and inner periphery of the insert 17 are stuck to the adjacent layers. The strip 24 consists of a conventional filter paper which is made electrically conductive by the application of an appropriate coating thereto, which coating does not destroy its filtering properties. As shown in Figure 1 and, on a larger scale, in Figure 2, a wire 27 leads from the contact pin 22 to a connector plate 28 which projects beyond one end surface of the filter insert 17 and which is rigidly connected to the outer end 25 of the strip 24 of filter material by means of a hollow rivet 29. As shown on a larger scale in Figure 3, a contact clip 31 engages the inner end 26 of the strip 24 of filter material, the lower end of the clip directly engaging the apertured plate 16 and thus producing an electrically conductive connection between the strip 24 and the apertured plate 16 and thus to the housing 11, which forms the negative terminal shown schematically at 32. The shape of the contact clip 31 can be seen in more detail in Figure 4. The filter insert 17 is sealed in the housing 11 by adhesive located at 33 and is separated from the inner wall of the cup-like portion 12 and from the apertured plate 16 by a cup-like insulating layer 34, the bottom portion of the layer 34 having openings 35 in the region of the apertured plate 16 so as to allow the filtered liquid to pass through. The terminals 21, 32 and the filter insert 17 thus form parts of an electrical heating device 36 in which the filter insert itself forms a heating resistance. The method of operation of the liquid filter 10 is as follows, its function only being discussed insofar as is necessary for the understanding of the invention. The diesel fuel to be cleaned flows through the inlet 19 into the housing 11, axially through the filter insert 17, upwards through the central tube 14 and out again through the outlet 18. If low temperatures prevail during operation, the paraffin tends to be precipitated out of the diesel fuel and to clog the pores of the strip 24 of filter material. The threshold of the ability to filter in respect of diesel fuel is established by DIN 51601; in accordance therewith, the temperature threshold for winter fuels at which the fuel must still be filterable, is - 120C. Such low temperatures can occur frequently with motor vehicles which left out of doors, that is not garaged. during winter. In order to facilitate filtration in these cases, a voltage is applied to the positive terminal 21 shortly before the engine is started, so that a current flows from the positive terminal 21, through the wire 27, the connector strip 28, from the end 25 to the end 26 of the strip 24 of filter material, through the contact clip 31, the apertured plate 16 and the housing 11 to the negative terminal 32. Heat is thus generated with the lowest possible electrical energy directly at the location at which it is also used, and the applied energy is used as efficiently as possible. Paraffin clogging the pores in the strip 24 of filter material is thereupon released and the diesel fuel can flow through the filter 17. It is a further advantage of this arrangement that it is only necessary to draw energy from the battery of the vehicle for a limited period. Modifications may be made in the illustrated embodiment within the scope of the present invention. Thus, the construction of the filter and the arrangement of the electrical terminals may be varied. WHAT WE CLAIM IS:

1. A filter for liquids, which comprises a housing having an inlet for liquid to be filtered and an outlet for filtered liquid and, within the housing, a filter insert consisting of a strip of electrical conductive filter paper spirally wound about an axial tube, the filter insert being arranged for axial flow of the liquid therethrough and being electrically connected to terminals on the housing so that the filter insert is adapted to constitute a resistance heating element.

2. A liquid filter according to claim 1, in which the housing is formed of metal, the axial tube of an electrically non-conductive material. the filter insert is separated from the housing by an electrically insulating layer and the inner and outer ends of the filter paper strip are electrically connected to the terminals.

3. A liquid filter according to claim 2, in which the housing comprises a cup portion and a cover and an apertured metal plate is located within the cup portion and serves to support the filter insert. and the outer end of the filter paper strip is electrically connected to a positive terminal mounted on the cover and inner end of the filter paper strip is electrically connected to the apertured metal plate, and thereby to the housing. through a contact clip.

4. A liquid filter according to claim 3, in which a connector strip is attached to the outer end of the filter paper strip by means of a hollow rivet.

5. A liquid filter substantially as herein

described with reference to the accompanying drawings.