The present invention relates to an expansion tank according to the preamble of patent claim 1. A cooling system with a circulating coolant for cooling of a combustion engine normally comprises an expansion tank that accommodates the coolant's volume change when it is heated and expands. The expansion tank usually comprises a lid that can be opened, and an inlet opening for refilling the coolant in the cooling system When the combustion engine is in operation, the coolant is thus heated and expands, so that an overpressure is created in the cooling system. The overpressure means that the coolant, without starting to boil, may circulate in the cooling system at a somewhat increased temperature in comparison with the temperature at atmospheric pressure.

On occasions where the level of the coolant sinks below a minimum level in the expansion tank, the lid must be opened for purposes of refilling coolant. If the coolant has been heated before the lid is opened, the overpressure created in the cooling system is eliminated. Following refilling with coolant, a certain amount of time is required before the desired overpressure is created in the cooling system. There is thus a risk of local boiling of the coolant in the cooling system, which may result in damaging the combustion engine and other components cooled by the coolant.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide an expansion tank, which makes it possible to open a lid in the expansion tank for refilling with coolant without eliminating an existing overpressure in the cooling system.

This objective is achieved with the arrangement of the type specified at the beginning, which is characterised by the features specified in the characteristics of patent claim 1. The expansion tank thus comprises a second chamber which is connected with the first chamber via a passage. The passage is sealable with a valve element. The expansion tank comprises a control mechanism which puts the valve element in an open position when the lid is in a fixed position. The lid is normally in a fixed position on the expansion tank on all occasions, except when the cooling system should be refilled with coolant. The first chamber and the second chamber are thus connected with each other when the cooling system is in operation. Thus the same overpressure is created in both chambers when the coolant is heated and expands in the cooling system. The control mechanism places the valve element in a closed position as soon as the lid is moved from the fixed position on the expansion tank. The passage between the chambers is thus closed when the lid is opened. The overpressure in the second chamber may thus be maintained when the lid has been taken off and the opening for refilling with coolant is exposed.

When the coolant has been refilled and the lid has been fastened in the fixed position again, the control mechanism opens the valve element and thus the passage between the first chamber and the second chamber. Thus, air may flow from the second chamber to the first chamber so that an overpressure is restored in the first chamber and the cooling system. With a suitable dimensioning of the chambers, an overpressure which is not significantly lower than the overpressure which prevailed in the cooling system before the lid was opened, may be restored in the first chamber and in the cooling system. The control mechanism for the valve element may be of any type. It may comprise suitably designed mechanical components which open and close the valve element depending on the position of the lid. The control mechanism may, alternatively, comprise a sensor which determines the position of the lid and a valve element controlled by signals from the said sensor regarding whether or not the lid is in the said fixed position.

According to one embodiment of the invention, the control mechanism comprises a sealing element in the form of a spring element, which is adapted to move the valve element to the closed position with a spring force. A suitably designed spring element normally provides a very secure closing function for a valve element. The control mechanism may comprise an opening element which is adapted to move the valve element from the closed position to the open position, against the action of the said spring element. With a suitably dimensioned spring element, the opening element may displace the valve element from the closed position to an open position with a relatively small force. According to one embodiment of the invention, the opening element is fixed on the lid and comprises an end portion which is adapted to come into contact with and move the valve element from the closed position to the open position, when the lid reaches the said fixed position. The opening element may be elongated and extends from the lid to the valve element when the lid is in the said fixed position. The force required to displace the valve element from the closed position to the open position is here achieved by the person who places the lid in the fixed position on the expansion tank.

According to one embodiment of the invention the expansion tank comprises a sealing element, which is adapted to prevent the first chamber from being connected with surrounding air for as long as the valve element is in the open position. It is necessary for the valve element to close the passage to the second chamber entirely before the first chamber is connected with air at the surrounding pressure. In order to ensure that this occurs, a sealing element may be arranged in a suitable place in connection with the inlet opening. The sealing element may provide a seal of the inlet opening during an initial stage when the cover is released from the fixed position.

According to one embodiment of the invention, the opening element extends from the lid to the valve element, via the inlet opening, when the lid is in the fixed position, whereby the said sealing element is adapted to seal a gap between an exterior surface of the opening element and an inner surface of the inlet opening. The sealing element may consist of an O-ring which is arranged around the opening element. The O-ring seals a gap between an exterior surface of the opening element and an interior surface in the inlet opening. As long as the O-ring is in the inlet opening, the overpressure in the first chamber may be maintained.

According to one embodiment of the invention, the lid is detachably arranged on a filling pipe which defines the inlet opening with screw threads. The lid is screwed on to the filling pipe until it reaches the said fixing position. With the help of the screw threads, the lid may be screwed into the fixed position with a suitable force which ensures that the lid is maintained in the fixed position during the operation of the cooling system.

According to one embodiment of the invention, the first chamber has markings for a minimum level and a maximum level for coolant. If the coolant level sinks below the minimal level in the expansion tank, the coolant must be refilled. Coolant is normally filled up to the maximum level in the expansion tank. The said passage between the first chamber and the second chamber is preferably located at a height level above the coolant's maximum level in the first chamber. This ensures that air may only be transferred from the first chamber to the second chamber. The passage may also have a design which makes it more difficult for liquid than for air to pass through the passage. The second chamber's volume above the maximum level for the coolant is preferably larger than the first chamber's volume above the maximum level for the coolant. Air occupies the volume located above the level of the coolant in the first chamber.. After the coolant has been refilled in the first chamber, there usually is coolant up to the maximum level in the expansion tank. With a maximum coolant level, the volume of air in the first chamber is relatively small. When the passage between the chambers is opened, the pressured air flows from the second chamber into the first chamber. The greater the volume of the second chamber in relation to the air volume in the first chamber, the greater an overpressure may be restored in the first chamber and in the cooling system when the lid is applied in the fixed position.

BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description, as an example, of a preferred embodiment of the invention with reference to the enclosed drawings, on which:

Fig. 1 shows an expansion tank according to the present invention, with a lid for refilling of coolant in a fixed position on the expansion tank,

Fig. 2 shows the lid in a first stage after it has been loosened from the fixed position and

Fig. 3 shows the lid in a second stage after it has been loosened from the fixed position.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1-3 show an expansion tank 1 for receipt of coolant which circulates in a cooling system which cools a combustion engine in a vehicle. The expansion tank 1 comprises a first chamber 2 for the receipt of coolant. The first chamber 2 comprises a marking for a maximum coolant level and a marking for a minimum coolant level. The coolant level in the expansion tank 1 must thus be between the minimum level and the maximum level. The expansion tank 1 comprises a filling pipe 3, on an upper side section. The filling pipe 3 has an interior inlet opening 4 for filling of coolant in the first chamber 2. A lid 5 with an interior screw thread 5a is adapted to be screwed on to an exterior screw thread 3a on the filling pipe 3.

The expansion tank 1 comprises a second chamber 6 which is arranged in connection with the first chamber 2. A passage 7 which links the first chamber 2 to the second chamber 6. The second chamber 6 otherwise consists of a sealed space. A valve element 8 is arranged to be moveable between a closed position where it seals the passage 7 and an open position where it opens the passage 7. The passage 7 is defined by a valve seat 7a which is arranged in the second chamber 6. The valve element 8 is pivoted between the closed position and the open position around a joint 8a.. A spring element 9 is arranged inside the second chamber 6. The spring element 9 is pretensioned around a joint 9a with the help of a first spring part 9b which abuts the interior wall surface in the second chamber 6, and a second spring part 9c which abuts the valve element 8 with a spring force. The second part 9c in the spring element 9 moves the valve element 8 toward the closed position.

The lid 5 is equipped with an elongated opening element 5b. The elongated opening element 5b is, at a fist end section 5b| , fixed to a central interior surface of the lid 5. The elongated opening element 5b thus constitutes an integrated part of the lid 5. When the lid 5 is in a fixed position on the filling pipe 3, the elongated opening element 5 b extends through the inlet opening 4, the first chamber 2 and the inlet opening 7. The elongated opening element 5b has a second end section 5b ₂ which is adapted to come into contact with the valve element 8 and move it into an open position against the action of the spring element 9, when the lid 5 is in the fixed position. The second end section 5b ₂ has a smaller cross sectional area than the opening element 5b otherwise has. It may therefore be led through the passage 7 more easily and reach the valve element 8. The elongated opening element 5b is equipped with protruding positioning element 5b ₃ for a sealing element in the form of an O-ring 10. The O-ring 10 is adapted to create an airtight seal between the elongated opening element 5b and an interior wall surface in the inlet opening 4. The O-ring 10 creates a sealing closure between the first chamber 2 and the surrounding air. Fig. 1 shows the lid 5 in the said fixed position on the expansion tank 1. Here, the elongated opening element 5b has displaced the valve element 8 in the open position. Thus, a similar pressure is obtained in the second chamber 6 as in the first chamber 2. The O-ring 10 on the elongated opening element 5b prevents the air in the first chamber 2 from leaking out into the surrounding areas. The screw threads 3a, 5a may also have a construction preventing such a leakage. During the operation of the combustion engine, the coolant circulating in the cooling system gets heated during cooling the combustion engine. The change in volume of the coolant, occasioned by its change of temperature, is absorbed by the expansion tank 1. The coolant's volume change and heating creates an overpressure in the cooling system. The overpressure means that the coolant may circulate in the cooling system without boiling, even when it has a temperature slightly higher than 100°C. The air which is located above the coolant in the first chamber 2 obtains an overpressure similar to the coolants. Since the valve element 8 is in the open position, a similar overpressure is obtained in the air in the second chamber 6. The O-ring 10 ensures that the air in chambers 2 and 6 does not leak into the surrounding areas via the inlet opening 4 and the lid 5.

Fig. 1 shows a coolant level A which is below the marked minimum level. The cooling system therefore has to be filled up with coolant.. Here, the coolant is warm and there is an overpressure in chambers 2 and 6 in relation to the surrounding pressure. The lid 5 is first unscrewed from the fixed position via the screw thread sections 3a and 5a. The lid 5 and the elongated opening element 5b are thus displaced somewhat to the left in the Figure. When this happens, the spring element 9 may swing the valve element 8 around the joint 8a to the closed position. The valve element 8 has an essentially flat surface, which in the closed position is pressed against the valve seat 7a of the spring element 9. When the valve element 8 reaches the closed position, the lid 5 is displaced from the fixed position.

Fig. 2 shows the valve element after it has reached the closed position. The valve element 8 here closes the passage 7 between the first chamber 2 and the second chamber 6. When this happens, the O-ring 10 still remains in the inlet opening 4, thus retaining the overpressure in the first chamber 2. Since the valve element 8 has now sealed the second chamber 6, the prevailing overpressure will be maintained in the otherwise sealed chamber 6, until the valve element 8 is moved into the open position next time. If one continues to loosen the lid 5 in the unscrewing direction, the O-ring 10 is successively moved to the left inside the inlet opening 4. As long as the O-ring 10 is located inside the inlet opening 4, the overpressure in the first chamber 2 is maintained. As soon as the lid has reached a position where the O-ring 10 leaves the inlet opening 4, the first chamber 2 is connected with the surrounding air. The pressure in the first chamber 2 is thereby reduced to the same pressure as the surrounding air. The air pressure in the first chamber 2 may be reduced while the threaded sections 3a and 5a are still engaged with each other, or after they have ceased to be engaged with each other.

Fig. 3 shows the valve element after the O-ring 10 has left the inlet opening 4. It is now possible to loosen the lid 5 and the elongated opening element 5b entirely from the expansion tank 1. The inlet opening 4 is now entirely exposed and coolant may be added to the first chamber 2 via the inlet opening 4. Coolant is now refilled up to a level B which corresponds to the maximum level. The elongated opening element 5b is then inserted into the inlet opening 4. The O-ring is also displaced into the inlet opening 4, creating a tight closure between the air in the first chamber 2 and the surrounding air. The air in the first chamber 2 as well as the pressure in the cooling system remain, however, at the pressure of the surrounding air. The screw threads of the lid 5a reach the filling pipe's screw threads 3a. The lid 5 is then screwed on to the filling pipe 3. The lid's 5 screwing movements displace the elongated opening element 5b successively to the right, until the second end section 5b ₂ reaches the valve element 8. Since the elongated element 5b is centrally arranged on the lid 5, it produces a clean rotation movement around a central shaft, without being displaced in a radial direction. The second end section 5b ₂ will eventually come into contact with the valve element 8. The second end section 5b ₂ then displaces the valve element 8 to an open position, against the action of the spring element 9. As soon as the valve element 8 has reached an open position, the lid has reached its fixed position. With the help of the screw threads, the lid 5 may be screwed on into the fixed position with a force that maintains the valve element in the open position.

In the open position, the passage 7 is exposed and air from the pressured second chamber 6 flows over to the first chamber 2. Thus, the same overpressure is created in both chambers 2 and 6. Thanks to the stored overpressure in the second chamber, an overpressure may again be created in the first chamber 2, and in the cooling system, when the lid 5 reaches the said fixed position. The overpressure created in the cooling system, however, is somewhat lower than the overpressure which prevailed in the cooling system before the lid 5 was opened. The extent to which the overpressure is lower is determined by the relationship between the volume above the coolant level B in the second chamber 6 and the first chamber's volume above the coolant level B. Preferably, the volume above the coolant level B in the second chamber 6 is significantly greater than the volume above the coolant level B in the first chamber 2, which normally corresponds to the maximum level after coolant has been refilled. With such a relationship between the volumes of chambers 2 and 6, a large part of the overpressure which prevailed in the cooling system before the lid 4 was opened may be recreated when the lid is screwed on. Thus, local boiling of the coolant in the cooling system and potential damage to the combustion engine or other components in the cooling system may be avoided. The invention is in no way limited to the embodiment described in the drawing, but may be varied freely within the framework of the patent claims.