FIELD OF THE INVENTION AND PRIOR ART The present invention relates to an expansion tank according to the preamble of claim 1 which is intended to form part of a cooling system of a motor vehicle.

A combustion engine of a vehicle is cooled by means of coolant which is circulated in a cooling system. When the engine is in operation it gives off heat to the coolant, which is thereby warmed and expands. The resulting total volume increase of the coolant in the vehicle's cooling system may amount to several litres and depends on the original coolant volume and the respective temperature increase. To prevent too much pressure increase in it, the cooling system is provided with an expansion tank which can accommodate the coolant surplus arising from the expansion. The coolant's boiling point rises with increasing pressure, which makes it desirable to maintain a certain positive pressure in the cooling system when the engine is in operation, and thereby prevent boiling. To make this possible and at the same time prevent dangerously high coolant pressure, the expansion tank is provided with an overpressure valve which ensures that the pressure in the tank cannot exceed a predetermined level. When the coolant expands through warming, the air present in the expansion tank is compressed, increasing the pressure in the tank and the rest of the cooling system. Another important function of an expansion tank of the type indicated above is that it should be possible for the coolant received in the tank to be vented in it before passing on in the cooling system. The air which is absorbed by the coolant circulating through the cooling circuits of the cooling system and which therefore accompanies the coolant to the expansion tank is intended to rise to the surface of the coolant volume accommodated in the expansion tank in order to accumulate in an air-filled space above the level of the liquid in the tank. The coolant in the expansion tank thus undergoes venting. Various measures have been adopted with a view to improving the venting characteristics of expansion tanks but there is still need for an expansion tank which affords good venting characteristics while maintaining a relatively space-saving configuration.

An expansion tank according to the preamble of claim 1 is known from DE 10050852 A1.

OBJECT OF THE INVENTION

The object of the invention is to propose an expansion tank with a novel and relatively simple and space-saving configuration and good venting characteristics. SUMMARY OF THE INVENTION

The present invention achieves said object by means of an expansion tank presenting the features defined in claim 1. The expansion tank according to the invention comprises - an outer casing ,

- an expansion chamber enclosed i n the casing and intended to accommodate coolant,

- an inlet aperture situated in the casing and intended to be connected to one or more venting li nes of said cooling system in order to allow inflow of coolant and air to the expansion chamber via th is apertu re,

- an outlet aperture situated in the casing and intended to be connected to a coolant line of said cooling system in order to allow outflow of coolant from the expansion chamber to th is coolant line via this aperture , and

- a divid ing wall situated in the casing and dividi ng the expansion chamber into an upper space above the divid ing wal l and the lower space below the divid ing wal l, said i nlet aperture being situated in the upper space and said outlet aperture i n the lower space.

The expansion tank according to the i nvention is characterised

- in that the dividing wall extends from a first sidewal l of the casing towards an opposite second sidewall of the casing ,

- that the u pper side of the dividing wall forms a downward- curving guide path adapted to gu iding a flow of coolant from the upper space to the lower space, wh ich gu ide path has an u pper end faci ng towards the first sidewal l and a lower end facing towards the second sidewall ,

- that the upper space is connected to the lower space via a gap between the lower end of the guide path and the second sidewall , and

- that an inlet basin is provided in the upper space such that the upper end of the gu ide path serves as an upper edge of the inlet basin and the inlet aperture leads into the inlet basin at a level below said upper edge so that the coolant flowing into the expansion chamber via the inlet aperture is caused to rise upwards in the inlet basin and then reach the guide path via said upper edge.

The coolant flowing into the expansion tank initially accumulates in the inlet basin and spreads out in it before overflowing to the guide path. In the inlet basin an initial venting of the coolant is effected by air bubbles rising to the surface of the coolant accommodated in the inlet basin to join the air in the air-filled upper part of the expansion chamber. From the inlet basin the coolant overflows to the guide path constituted by the dividing wall. With suitable dimensioning of the expansion tank relative to the coolant flow through it, the layer of coolant formed on the guide path will be so thin that the air bubbles which accompany the coolant flowing along the guide path can very easily join the air above the guide path. A further venting of the coolant thus takes place during its passage along the guide path. The guide path curving downwards means that the coolant can be caused to slip down in a relatively gentle way, without any sudden jerking, into the coolant accumulated in the lower part of the expansion chamber, thus limiting the amount of air in the form of bubbles which is drawn down into the coolant leaving the guide path. Their ability to rise will also cause the greater part of these air bubbles to rise immediately back up to the air. Having the coolant enter the expansion tank via the aforesaid inlet basin and the guide path makes it possible to achieve effective initial venting of the inflowing coolant in a space-saving way. This initial venting makes it easier to achieve a fu lly vented coolant outflow from the expansion chamber.

In one embodiment of the i nvention the gu ide path comprises a gently sloping and straight, or at least su bstantially straight, first section , a cu rved second section and a sharply sloping and straight, or at least substantially straight, third section , such that said first section extends from the upper end of the gu ide path to an upper end of the second section , the second section extends in an arc between the first and third sections, and the third section extends from the lower end of the second section to the lower end of the gu ide path. The gu ide path being provided with a gently sloping initial section and a sharply sloping final section makes it possible for the initial section to be so arranged that it extends across a relatively large part of the length of the expansion chamber while at the same time the flow velocity of the coolant along the initial section is lim ited, which is advantageous with regard to venting effect. According to another embodiment of the invention the d ivid ing wall comprises a portion wh ich extends from the first sidewall to the u pper end of the gu ide path such that the inlet basin is del ineated from the lower space by th is portion of the dividing wall . This makes it constructionally easy to provide the in let basin in the expansion chamber.

According to another embodiment of the invention the upper part of the lower space is connected to the u pper part of the upper space by an air duct wh ich extends through the d ividing wall and which allows air to flow from the lower space to the u pper space. According to another embodiment of the invention the air duct takes the form of a pipe fastened to , and protrud ing vertically upwards from, the d ividing wall . Th is is a constructionally simple way of providi ng the respective air duct.

According to another embodiment of the invention a labyrinthine flow duct is provided for the rad iator liqu id in the lower space and extends between said gap and the outlet aperture . The coolant in the lower space is thus provided with a relatively long flowpath , so the air bu bbles which remain in the coolant flowing into the lower space have time to rise to the surface of the coolant volu me accom modated in the lower space and accu mulate in the air pocket above the liqu id level in the lower space, thus allowing effective final venti ng of the coolant before it leaves the expansion chamber.

According to another embodiment of the invention a plurality of intermediate walls are provided in the lower space to form said labyrinthine flowduct. This is a constructionally simple way of creating the labyri nth ine flowduct. The intermediate walls extend with advantage vertically between a bottom surface in the lower space and the u nderside of the d ividi ng wall . According to another embodiment of the invention said in let aperture takes the form of an elongate horizontal gap resu lting in an initial spreadi ng of the coolant enteri ng the in let basin . Other advantageous features of the expansion tank according to the invention are indicated by the dependent claims and the description set out below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below in more detail on the basis of embodiment examples with reference to the attached drawings, in which

Fig. 1 depicts a side view of an expansion tank according to a first embodiment of the present invention,

Fig.2 depicts a perspective view of the expansion tank according to Fig.1 ,

Fig.3 depicts a perspective view corresponding to Fig. 2 but with the addition of a schematically depicted flow of coolant through the expansion tank,

Fig.4 depicts a cross-section along the line IV-IV in Fig.1,

Fig.5 depicts a perspective view of an expansion tank according to a second embodiment of the present invention, and

Fig.6 depicts a schematic diagram of a cooling system provided with an expansion tank according to the present invention. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Figs. 1-4 illustrate an expansion tank 1 according to an embodiment of the present invention which is intended to form part of a cooling system of a motor vehicle, e.g. a cooling system 50 of the type depicted in Fig. 6. The tank comprises an outer casing 2 of rigid material, e.g. a plastic, and an expansion chamber 3 delineated by the casing. In the example illustrated the casing comprises a base element 2a fitted with a sideplate 2b (see Fig. 4) which forms a longside wall of the casing. The sideplate is adapted to being fastened to a flange 4 of the base element 2a, e.g. by threaded connections. Figs. 1-3 show the expansion tank with the sideplate removed.

The casing 2 is provided with an outlet aperture 5 (see Fig. 2) which is intended to be connected to a coolant line of a cooling system in order to allow coolant exchange between the expansion chamber 3 and other parts of the cooling system via this aperture. The aperture 5 is situated in the bottom of the expansion chamber. A pipe stub 6 connected to the aperture 5 protrudes from the underside of the casing. Said coolant line is intended to be connected to this pipe stub. The casing 2 is provided with two inlet apertures 7 (see Fig. 2) each intended to be connected to its respective venting line of said cooling system in order to allow inflow of coolant and air from the venting lines to the expansion chamber 3 via these inlet apertures. The apertures 7 are situated in a sidewall 8 of the casing. Each aperture 7 is connected to a pipe stub 9 which protrudes from the casing's sidewall 8. Said venting lines are intended to be connected to these pipe stubs 9. The casing might alternatively be provided with only one inlet aperture 7 for connecting to a venting line of the cooling system. As a further alternative, the casing might be provided with more than two inlet apertures.

The casing 2 is also provided with a closable filling aperture 10 via which coolant can be introduced into the expansion chamber to replenish said cooling system. This filling aperture may be closed by means of a removable cover (not depicted).

An overpressure valve 11 for limiting the pressure in the expansion chamber 3, and a return valve 12, are situated on a wall 13 of the casing 2. These valves 11, 12 are depicted schematically in Figs. 1-3. In the embodiment illustrated said wall 13 is an upper wall of the casing's base element 2a. In the example illustrated said valves 11, 12 are situated at a distance from one another in their respective apertures in said wall, but might alternatively be close to one another in a common valve unit situated in a larger aperture in said wall. The overpressure valve 11 allows air and coolant to flow out from the upper part of the expansion chamber 3 when coolant volume increase results in a higher positive pressure in the expansion chamber than a level set by the overpressure valve. The return valve 12 allows air to flow into the upper part of the expansion chamber from the surroundings when coolant volume decrease results in a lower negative pressure in the expansion chamber than a level set by the return valve. A dividing wall 1 6 situated within the casi ng 2 divides the expansion chamber 3 into an u pper space 3a above the d ivid ing wall and a lower space 3b below the divid ing wall. The in let apertures 7 are situated in the upper space 3a and the outlet aperture 5 is situated in the lower space 3b. The dividi ng wall extends from a first sidewall 8 of the casing towards an opposite second sidewall 1 7 of the casing . The dividing wal l has a width corresponding to the distance between the sideplate 2b and the opposite sidewall 8 of the casing . The d ivid ing wall has a first longitudinal edge 1 9a (see Fig . 2) wh ich abuts seal ingly against the sideplate 2b, and an opposite second longitudinal edge 1 9b which abuts sealingly against the sidewall 8.

The upper side of the dividing wal l forms a downward-curving gu ide path adapted to gu iding a flow of coolant from the upper space 3a to the lower space 3b. This gu ide path has an upper end 21 facing towards the first sidewall 8 and a lower end 22 facing towards the second sidewall 1 7. The divid ing wall's lower end 22 is situated at a distance from the second sidewall 1 7 in such a way as to leave between them a gap 23 which serves as a flow connection between the upper space 3a and the lower space 3b.

An inlet basin 25 is provided in the u pper space 3a. The upper end 21 of the gu ide path serves as an upper edge 26 of the gu ide path and the inlet apertures 7 lead into the inlet basin at a level below said upper edge 26 so that the coolant flowing into the expansion chamber 3 via the apertures 7 is caused to rise i n the inlet basin and thereafter reach the gu ide path 20 via said u pper edge 26. The gu ide path 20 comprises a gently sloping but straight, or at least su bstantially straight, first section 20a, a curved second section 20b and a sharply sloping but straight, or at least substantially straight, third section 20c. The first section 20a extends from the upper end 21 of the guide path to an upper end 27 of the second section 20b and slopes gently downwards from the upper end 21 of the gu ide path to the upper end 27 of the second section , towards the second sidewal l 1 7 at an angle a of 5-1 5 ^Q relative to the horizontal plane . The second section 20b itself extends in an arc from a lower end 28 of the first section 20a to an upper end 29 of the th ird section 20c. The third section extends from a lower end 30 of the second section 20b to the lower end of the gu ide path and slopes sharply downwards from the lower end 30 of the second section to the lower end 22 of the gu ide path , towards the second sidewal l 1 7 at an ang le β of 5-1 5 ^Q relative to the vertical plane . The third section 20c of the guide path delineates in conju nction with the second sidewall 1 7 a wedge-shaped space 3c within the expansion chamber 3.

In the embod iment illustrated the d ividing wall 1 6 comprises a portion 31 which extends from the first sidewal l 8 to the upper end 21 of the gu ide path , such that the inlet basin 25 is del ineated from the lower space 3b by th is portion 31 of the dividing wall .

The upper part of the lower space 3b is connected to the upper part of the u pper space 3a by an air duct 32 which in the example illustrated extends through the divid ing wall 1 6 near the upper end 21 of the gu ide path . The air duct takes with advantage the form of a pipe 33 which is fastened to, and extends vertically upwards from, the dividing wall 16, as depicted in Figs. 1-3. The pipe 33 is open at both ends and has at its lower end an inlet aperture connected to a hole which runs through the dividing wall. At its upper end the pipe has an outlet aperture leading into the upper part of the upper space 3a.

In the lower space 3b there is a labyrinthine flowduct 35 for the radiator liquid between the aforesaid gap 23 and the outlet aperture 5. In the embodiment illustrated this flowduct is bounded by a number of intermediate walls 37, 38 situated in the lower space 3b. Each of the intermediate walls extends vertically between a bottom surface 39 in the lower space 3b and the underside 40 of the dividing wall. Every second intermediate wall 37 has a first longitudinal edge 41a (see Fig.4) which abuts sealingly against the sidewall 18, and an opposite second longitudinal edge 41b situated at a distance from the sideplate 2b, resulting in, between the second longitudinal edge and the sideplate, a gap which serves as a flow passage for the coolant. The other intermediate walls 38 each have a first longitudinal edge 43a which abuts sealingly against the sideplate 2b, and an opposite second longitudinal edge 43b at a distance from the sidewall 18, resulting in, between the second longitudinal edge and the sidewall, a gap which serves as a flow passage for the coolant. In the example illustrated there are five intermediate walls, 37, 38 in the lower space 3b, but their number may of course be larger or smaller. It is of course also possible for the labyrinthine flowduct 35 in the lower space to be configured in some other way than as herein described. Fig. 3 illustrates the flow of coolant through the expansion chamber 3. Coolant and accompanying air bubbles are led into the inlet basin 25 from one or more venting lines via the inlet apertures 7. In the inlet basin an initial venting of the coolant is effected by air bubbles rising to the surface of the coolant accommodated in the inlet basin and joining the air above the liquid surface. From the inlet basin the coolant runs over to the guide path 20 via the upper edge 26 of the inlet basin. The inlet basin provides assurance that the coolant will flow along the guide path in a well-distributed flow so that a thin layer of coolant is formed on the first and second sections 20a, 20b of the guide path. As it passes along these first and second sections, the coolant undergoes further venting in that air bubbles accompanying it come into contact with and join the air above the layer of liquid on the guide path. The coolant then leaves the guide path via the curved second section 20b and slips down into the liquid volume accumulated in the wedge- shaped space 3c between the third section 20c of the guide path and the second sidewall 17. When it leaves the guide path 20 and reaches the surface of the coolant volume in the wedge- shaped space 3c, the coolant will carry down with it into the liquid a small amount of air in the form of bubbles. Some of these bubbles will immediately rise to the surface of the coolant volume in the wedge-shaped space and join the air above the liquid surface, while others will cling to the surface of the third section 20c of the guide path before becoming detached and rising to and joining the air above the surface of the coolant volume in the wedge-shaped space. The coolant will then flow further into the space 3b below the dividing wall 16 via the gap 23. In said space 3b the coolant is led through the labyrinthine flowduct 35 before finally leaving the expansion chamber 3 via the outlet aperture 5. During its passage through the labyrinthine flowduct, the coolant undergoes a final venting in that remaining air bubbles will rise to the surface of the coolant volume in the labyrinthine flowduct and join the air above the liquid surface. The air volume accumulated above the liquid surface in the space 3b below the dividing wall 16 is in communication via the air duct 32 with the air volume accumulated in the space 3a above the dividing wall so that air can flow freely between these air volumes.

Fig.5 illustrates an alternative embodiment in which the casing 2 of the expansion tank is provided with an inlet aperture 7' in the form of an elongate horizontal gap. This embodiment corresponds otherwise to that illustrated in Figs. 1-4 and described above.

Fig. 6 illustrates schematically a cooling system intended for a motor vehicle, comprising a cooling circuit 51 for cooling a combustion engine 52 of the vehicle by means of a coolant flowing in the cooling circuit, preferably in the form of water possibly with freezing point additives such as glycol. A coolant pump 53 is provided in the cooling circuit to circulate the coolant in the circuit. In addition, a radiator 54, e.g. in the form of a conventional coolant radiator, is provided in the circuit to cool said coolant. This radiator has a coolant inlet 55a connected to a coolant outlet 56b of the engine 52 via a first line 57 of the circuit, and a coolant outlet 55b connected to a coolant inlet 56a of the engine via a second line 58 of the circuit. In the example illustrated the coolant pump 53 is situated in the second line 58. The first line 57 is connected to the second line 58 via a th ird line 59 of the circu it to allow coolant to be led back from the eng ine's coolant outlet 56b to the eng ine's coolant inlet 56a without passing through said radiator 54. The th ird line 59 thus serves as a bypass line via wh ich coolant circu lati ng in the cooling circu it 51 can be led past the radiator 54 on its way between the coolant outlet 56b and the coolant in let 56a of the eng ine . The coolant is circu lated between the eng ine's coolant inlet and coolant outlet through coolant ducts (not depicted) withi n the engine, thereby absorbing heat from the engine . A thermostat 60 is provided at the ju nction point between the first line 57 and the third line 59. Depending on the temperature of the coolant, the thermostat will either lead the coolant flowing out of the engine to the rad iator 54 for cooling therein before being led back to the eng ine 52, or wil l lead it back directly to the eng ine via the third line 59 without passing through the radiator.

The coolant flowing through the rad iator 54 is cooled by air wh ich is blown towards the radiator when the vehicle is in motion . The cooling system 50 may also comprise a fan (not depicted) to generate an air flow throug h the rad iator. Th is fan may be connected to , in order to be driven by, the engine 52.

The cooling system 50 is provided with an expansion tank of the type described above . The tank's outlet aperture 5 is connected to the aforesaid second line 58 via a fourth line 61 of the cool ing system . This fourth line is connected to the second line 58 at a poi nt situated between the radiator 54 and the coolant pu mp 53. The tank's in let apertu res 7 are connected to the radiator 54 via a first venting line 62 and to the coolant ducts in the engine 52 via a second venting l ine 63. Coolant is led into the expansion chamber 3 with in the expansion tank 1 via the venting lines 62, 63 and is led back from the expansion chamber to the cooling circuit 51 via the aforesaid fourth line 61 after venti ng in the expansion chamber.

The expansion tank accord ing to the invention is particu larly intended for use in a heavy motor vehicle , e.g . a bus, a tractor vehicle or a truck.

The invention is of course in no way restricted to the embod iments described above , since nu merous possibi lities for mod ifications thereof are likely to be obvious to one skilled in the art, without thereby deviating from the invention's basic concept such as defined in the attached claims.