GB2452070A - Cooling System Expansion Tank - Google Patents

Abstract

An expansion tank 21 for an engine cooling system comprises a housing 20 formed by a lower moulding 24 and an upper moulding 25 joined at a joint plane 31. The external walls of lower moulding 24 include a deep side wall 43, a small bottom wall 46, an inclined wall 36 and a short near-vertical wall 37 which form a relatively deep tank portion. Parallel webs 44, 45 form a passageway 47 which is intersected by an array of intersecting webs 48 arranged in a parallel formation, the intersecting webs 48 being formed alternately on one side and the other of the passageway 47 and extending alternately from the deep side wall 43 and a transverse web 38. Each of the intersecting webs 48 has a side edge which extends substantially perpendicularly from the joint plane 31 towards the external wall and intersects the external wall at an obtuse angle which is achieved by giving each side edge a curved portion 49 where it intersects the external wall, the curved portion having a radius of at least 10mm and more preferably 20mm. Similar webs have similar curved portions, these allowing the stresses induced by the internal pressure of the cooling system (approximately 1 bar) to be spread over an area of the adjoining external wall which is considerably greater than the normal cross-section of the web where it meets the joint plane 31.

Description

Cooling System Expansion Tank This invention relates to expansion tanks for the cooling systems of liquid cooled internal combustion engines.

A typical cooling system expansion tank is a closed vessel which, when the engine is at rest, is only partially filled with liquid coolant, the remainder of the space above the liquid being available for the volumetric expansion of the coolant due to heat. Coolant discharged from the engine flows into the tank above the level of liquid coolant and returns from the bottom of the tank to join the flow of coolant returned to the engine. Such an expansion tank also serves as a means of enabling gases dissolved or trapped in the coolant to rise to the liquid surface and escape. Furthermore, air above the liquid surface becomes heated by the incoming coolant, thereby further helping to pressurise the cooling system and prevent cavitation in a circulation pump.

Known expansion tanks can have several drawbacks in terms of their ability to dissipate trapped air, to pressurise rapidly and to enable manufacture without expensive tooling.

An object of the present invention is provide an expansion tank which can incorporate features which address some or all of these problems.

According to the present invention there is provided an expansion tank for the cooling system of a liquid-cooled internal combustion engine, the tank comprising a housing having external walls and a plurality of internal walls or baffles which define chambers or passages in the housing, the housing being moulded from a plastics material as first and second components each defining at least a respective one of the external walls and a peripheral rim defining a respective joint face, the baffles being moulded integrally with the external walls, said components being joined together at a joint plane defined by the joint faces, the baffles in the first component including structural walls which extend to the joint plane and are joined at the joint plane to corresponding baffles in the second component, wherein at least some of the structural walls each has a side edge which extends substantially perpendicularly from the joint plane towards one of the external walls and intersects the external wall at an obtuse angle.

Preferably the side edge has a curved portion where it intersects the external wall.

The curved portion may have a radius of at least 10mm and, more preferably, at least 20mm.

In use of tank, the joint plane is preferably substantially horizontal and the first component is below the second component. In such a case, a passageway may be defined between a first wall and a second wall of the first component, the first wall comprising one of the external walls or one of the structural walls and the second wall comprising another of the external walls or another of the structural walls, the passageway being intersected by an array of the structural walls arranged in a parallel formation, the structural walls of the array being formed alternately on one side and the other of the passageway and extending alternately from the first wall and the second wall.

The invention will now be described by way of example and with reference to the accompanying drawings, of which:-Fig.1 is a diagrammatic representation of the cooling system of a liquid cooled internal combustion engine incorporating an expansion tank according to the invention; Fig.2 is a partially cross-sectioned side elevation of the expansion tank shown in Fig.1; Fig.3 is a cross-sectional plan view on the line Ill-Ill in Fig.2; and Fig.4 is an enlarged view of the area within the circle A in Fig.2 Referring to Fig.1, an internal combustion engine 11 has a pump 12 which can deliver liquid coolant (e.g., a water/antifreeze mix) through the engine 11 to an engine delivery hose 13 and a heat exchanger in the form of a conventional air cooled radiator 14. Flow from the radiator 14 back to the pump 12 passes through a radiator return hose 15, a thermostatically controlled bypass valve 17, and a pump return hose 16. The control valve 17 operates to control flow in the radiator return hose 15 and in a bypass hose 18 such that until the coolant reaches higher temperatures most of the flow of coolant from the engine 11 is through the bypass hose 18 and there is no flow through the radiator 14. At higher coolant temperatures, most of the flow passes through the radiator 14.

An expansion tank 21 has a tank feed hose 22 connected to the radiator 14 (or to any convenient point in the engine delivery hose 13) and a tank return hose 23 connected to the pump return hose 16. A heater matrix 19 for the heating a vehicle passenger compartment is also connected between the engine delivery hose 13 and the pump return hose 16.

With further reference to Figs. 2 and 3, it can be seen that the expansion tank 21 comprises a housing 20 having external walls and a plurality of internal walls or baffles which define chambers or passages in the housing. The tank 21 is formed from two generally dish-shaped moulded components 24, 25 each defining at least a respective one of the external walls and having a peripheral rim defining a respective joint face 26, 27.

The peripheral rims are joined together at a substantially horizontal joint plane defined by the joint faces 26 and 27 to give a hollow body of a generally rectangular cross-section.

The moulded components, more conveniently referred to as the lower moulding 24 and the upper moulding 25, are made of a suitable engineering plastics material, e.g. polyamide, glass reinforced polypropylene, polycarbonate, etc. and are welded or otherwise joined and sealed together by any suitable technique, for example hot plate welding. Mounting brackets (not shown) are formed integrally with the mouldings 24 & 25 on their external surfaces.

At one end of the upper moulding 25 there is a filler neck for closure by a filler cap 34 and at the other end an inlet port 35 for connection to the tank feed hose 22. The filler cap 34 incorporates the usual pressure control valve and anti-vacuum valve. In the lowest region of the lower moulding 24 there is an outlet port 40 for connection to the return hose 23.

The interior of the housing 20 is subdivided into passageways and chambers by internal divider walls or baffles which are formed from webs shown generally at 28 and which are moulded integrally with each moulding 24, 25. Most, but not all of the webs 28 which form the internal divider walls in one moulding form structural walls which are matched by a corresponding web in the other moulding and are joined together at the horizontal joint plane 31. However, there may be other webs 28 which are not matched in this way. The webs 28 thus help to reinforce the tank by interconnecting the external walls of the housing 20.

The inlet port 35 is in the upper moulding 25 above an inlet chamber 29 defined by webs 32, 31 in the lower moulding 24 and, as shown ghosted in Fig.3, has an inlet orifice 36 which lies tangential to a deflector 41 in the form of a vertical tubular cylinder which is open at its lower end. The deflector 41 extends below the horizontal joint plane to a level approximately midway between maximum and minimum cold fill levels of the tank 21. The deflector is arranged so that liquid coolant flowing into the enclosed chamber through the inlet orifice impinges upon the deflector tangentially or at an oblique angle as described in GB2403 1 63A.

In the example shown in Figs. 1 to 3, the external walls of lower moulding 24 are arranged so that there is a large bottom wall 41 and a low side wall 42 which form a relatively shallow tank portion in a region adjacent the inlet chamber 29 while a deep side wall 42, a small bottom wall 46, an inclined wall 36 and a short near-vertical wall 37 form a relatively deep tank portion in a region adjacent the outlet port 40. Substantially in line with the near-vertical external wall 37 is a transverse web 38 which extends across the lower moulding 24 but has deep U-shaped slots 39 which extend almost to the small bottom wall 46.

Parallel to the transverse web 38 are two parallel webs 44, 45, also with deep U-shaped slots 39, the parallel webs 44, 45 extending towards a level chamber 51 where a hollow pillar 52 extends from the small bottom wall 46 to guide a float (not shown). The float carries a magnet to operate a reed switch inside the pillar 52 for a low coolant level warning circuit. The level chamber 51 is directly below the filler cap 34 which allows for replacement of the float if required.

The parallel webs 44, 45 and the deep side wall 43 form a passageway 47 which is intersected by an array of intersecting webs 48 arranged in a parallel formation, the intersecting webs 48 being formed alternately on one side and the other of the passageway 47 and extending alternately from the deep side wall 43 and the transverse web 38. This is best seen in Fig.2 where the sectioned portion is on the line li-Il in Fig.3 and where one intersecting web 48 is shown extending from the external wall and another intersecting web 48 web is shown extending from the inclined wall 36, the short near-vertical wall 43 and transverse web 38.

Each of these intersecting webs 48 has a side edge which extends substantially perpendicularly from the joint plane towards the external wall and intersects the external wall at an obtuse angle B of approximately 150 degrees as particularly shown in Fig.4.

This angle of intersection B is achieved by giving each side edge a curved portion 49 where it intersects the external wall, the curved portion having a radius of at least 10mm and more preferably 20mm. Indeed, all of the webs 28 have similar curved portions, these allowing the stresses induced by the internal pressure of the cooling system (approximately 1 bar) to be spread over an area of the adjoining external wall which is considerably greater than the normal cross-section of the web (e.g. where it meets the joint plane 31).

To further reduce stresses, the external walls are slightly domed away from the webs where the webs adjoin the external wall, giving a quilted appearance. Nevertheless, in the case of the top moulding where there is a top waIl 54 which is immediately visible when the engine 11 is in a motor vehicle and an engine compartment lid or bonnet is lifted, transverse grooves 55 are moulded where the transverse web, the parallel webs 44 45 and other webs parallel to these adjoin the top wall. Other webs in the upper moulding 25 which adjoin the top waIl 54 are made thinner to avoid or minimise sink marks arising as a part of the moulding process.

In use, warm coolant from the engine 11 is pumped by the pump 12 into the delivery hose 13 through the tank feed hose 22 and into the expansion tank 21 through the inlet port 35 and into the inlet chamber 29. From the inlet chamber 29 the coolant can flow through the relatively shallow tank portion above the large bottom wall 41 towards the transverse web 38 where it flows through the slots 39 and into the passageway 47. At relatively low engine speeds when the coolant flow is low, coolant can take the more direct route between the inlet chamber 29 and the outlet port 40 so that most flow is through the slots 39 closest to the outlet port. However, at higher engine speeds, there is a greater flow which causes more flow in the passageway 47. The arrangement of intersecting webs 48 induces a longer and more tortuous path for the coolant which allows for a lower velocity and more time for air and trapped vapour to escape to the surface. The curved portions 49 of the intersecting webs 48 also help to lower the velocity of the coolant.

Claims (7)

1. An expansion tank for the cooling system of a liquid-cooled internal combustion engine, the tank comprising a housing having external walls and a plurality of internal walls or baffles which define chambers or passages in the housing, the housing being moulded from a plastics material as first and second components each defining at least a respective one of the external walls and a peripheral rim defining a respective joint face, the baffles being moulded integrally with the external walls, said components being joined together at a joint plane defined by the joint faces, the baffles in the first component including structural walls which extend to the joint plane and are joined at the joint plane to corresponding baffles in the second component, wherein at least some of the structural walls each has a side edge which extends substantially perpendicularly from the joint plane towards one of the external walls and intersects the external wall at an obtuse angle.

2. A tank according to claim 1 wherein the side edge has a curved portion where it intersects the external wall

3. A tank according to claim 2 wherein the curved portion has a radius of at least 10mm.

4. A tank according to claim 2 wherein the curved portion has a radius of at least 20mm.

5. A tank according to any preceding claim wherein, in use of tank, the joint plane is substantially horizontal and the first component is below the second component.

6. A tank according to claim 5 wherein a passageway is defined between a first wall and a second wall of the first component, the first wall comprising one of the external walls or one of the structural walls and the second wall comprising another of the external walls or another of the structural walls, the passageway being intersected by an array of the structural walls arranged in a parallel formation, the structural walls of the array being formed alternately on one side and the other of the passageway and extending alternately from the first wall and the second wall.

7. An expansion tank for the cooling system of a liquid-cooled internal combustion engine substantially as described herein with reference to the accompanying drawings.