GB2286675A

GB2286675A - Case for thermostat

Info

Publication number: GB2286675A
Application number: GB9502323A
Authority: GB
Inventors: Alain Bernard Armand Bouloy; Jean-Pierre Chamot
Original assignee: Vernet SA
Current assignee: Vernet SA
Priority date: 1994-02-18
Filing date: 1995-02-07
Publication date: 1995-08-23
Anticipated expiration: 2015-02-07
Also published as: IT1275226B; GB9502323D0; ITMI950221A1; GB2286675B; FR2716519B1; FR2716519A1; ITMI950221A0; DE19504677C2; DE19504677A1

Description

Inte-grated Case Thermostats 2286675 The present invention relates to

improvements in thermostats of the type which comprise a case and a thermostatic element in the case and in which the displacement of a movable part of the thermostatic element under the effect of the temperature of a fluid in the case acts on an element which is controlled by the thermostatic element, for example a valve in the case of a thermostatic valve. The invention can be used more particularly but not exclusively in thermostats for regulating fluid flow, for example the flow of cooling fluid in an internal combustion engine.

For such integrated case thermostats, it is, for many reasons and particularly with regard to the ease and cost of production, desirable to provide a case moulded from synthetic plastics material in which the thermostatic element is fixed. However, the use of a plastics case is fraught with problems inherent in the plastics material and in particular the low resistance to plastic flow, the poor resistance to vibrations, fluctuations in characteristics in course of time, etc. These problems are particularly difficult to resolve in the case of thermostats which are situated in difficult environments such as thermostats in the cooling circuit of internal combustion engines which are subjected to considerable fluctuations in temperature, to mechanical stresses and to very high pressures as well as to intense vibrations.

For this purpose, thermostats are already in use in which the thermostatic element is fixed by a peripheral portion between two separable plastics casing parts of generally tubular form, between which a sealing gasket is interposed, the two parts of the casing being connected to each other and fixed by two or three screws to the sealing gasket of the thermostat.

The cases of these thermostats are not very strong, have a short effective life and offer considerable risks of leakage. Furthermore, the case is incapable of accommodating the reactions of the spring of the thermostat element so that in conventional manner the thermostatic element must comprise stirrup members to contain the axial stresses of the parts of the thermostatic element.

It is for this reason that the thermostat is normally integrated into a strong case, particularly an aluminium case. Such cases may advantageously comprise lugs which extend parallel with the body of the thermostat and which have at their free end notches which accommodate a cross member or bridging piece fixed on the body of the thermostatic element and adapted to receive the reaction of the spring which seeks to push the thermostatic element back in the opposite direction to that in which it is displaced under the effect of increasing temperature.

However, this solution cannot be transposed to thermostats which have cases of plastics material and which in the long run are incapable of withstanding the reaction of the spring of the thermostatic element and the mechanical and hydraulic vibrations emanating from the engine and its hydraulic cooling circuit.

The object of the invention is to provide a thermostat in which the case is entirely or substantially of plastics material.

The invention consists in a thermostat of the type comprising a plastics case with a body of generally tubular form and having at least two openings for the inlet and outlet of a fluid, and a thermostatic element capable of expansion under the effect of an increase in temperature, the thermostatic element comprising at least one first fixed part adapted to bear against a support fixed in relation to the case and at least one second movable part adapted to move relative to the first part under the influence of a fluctuation in temperature, and to be restored by a spring, characterised in that the case comprises a first part of tubular form in which the thermostatic element is positioned and which has a springretaining means biased in tension by the thrust of the spring, and a second part having support elements adapted to receive the thrust of the spring in a direction tending to compress the support elements, the support elements being designed to accommodate the thrust of the spring when the two parts of 1 the case are assembled and thus to relieve the retaining means of the biasing of the spring.

Within the meaning of the present invention, the term 'plastics material' is understood to embrace synthetic materials whether they be thermoplastic or thermo-setting or other types.

In an advantageous embodiment, the thermostat comprises a transverse member having two oppositely directed faces, one of which receives the thrust of the spring while the other is applied against the support elements in such a way as to transmit to the support elements the thrust of the spring tending to compress the support elements.

According to a particularly advantageous embodiment of the invention, the part of the case which does not comprise the support elements may have elongated arms carrying notches adapted to receive the end of such a transverse member against which the spring bears so that the arms are subjected by the spring to a biasing in tension so long as the two parts of the case are not assembled the one to the other, whereas in the assembled state, when the support parts come in contact with the said transverse member, they raise it and remove the loading from the arms which are thus relieved.

In this way, the thermostatic element may be fitted in the case beforehand, prior to final installation in the plant in which the thermostat is to be used. The arms on the first part of the case may perfectly well withstand the biasing of the spring in tension under storage conditions whereas, when the thermostat is operating in a difficult environment, the arms are freed, the thrust of the spring being taken up by the support elements which are biased solely in compression, on a large bearing surface and in consequence they offer quite substantial strength and length of working life, compatible with prolonged use in a difficult environment.

Advantageously, the end- of the other movable element of the thermostatic element may be received in a cross member or bridging member moulded into the tubular part of the first part of the case and which may be of suitable dimensions.

According to another preferred feature of the invention, the fixing of the two parts of the case to each other may be carried out without the use of screws. In accordance with this feature, there is provided on one of the parts of the case, for example that which carries the support elements, a bearing surface against which is applied another bearing surface on the other part of the case, a rapid fixing means retaining the other part against the bearing surface of the first part. This rapid fixing means may for example be a rapid screw thread obtained directly by being moulded onto the first element around the bearing surface and cooperating with a complementary nut which may be for example of aluminium or of moulded plastics material.

Another solution consists of a deep-drawn sheet metal or plastics ring adapted to be fixed by a bayonet-type fixing, thanks to corresponding ramps on the said case element, the ring comprising one or more tongues adapted to be folded back, upon completion of fixing, into a position in which they penetrate indented parts of the case in order to lock the ring so that it cannot rotate.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 shows a cross-section through a thermostat according to a first embodiment of the invention; Fig. 2 shows a partial section taken on the line A-A in Fig. 1; Fig. 3 represents a partial cross-section taken on the line B-B in Fig. 1; Fig. 4 represents a partial view of Fig. 1 at the level of the support elements in a direction at right-angles to that of Fig. 1; Fig. 5 represents a cross-section through another embodiment of the :P invention; Fig. 6 represents a view of a support part in a direction at right-angles to that of Fig. 5; Fig. 7 shows a sectional view taken on the line A-A in Fig. 5 prior to locking; Fig. 8 shows a view similar to that in Fig. 7 after locking; Fig. 9 shows a cross-sectional view of a third embodiment of the invention; Fig. 10 shows a view of the support part in a direction at right-angles to that of Fig. 9; Fig. 11 shows a sectional view taken on the line A-A prior to locking and Fig. 12 shows a view similar to that in Fig. 11 after locking.

Firstly, reference will be made to Figs. 1 to 4.

The thermostat shown comprises a case consisting of two parts 1, 2 of synthetic plastics material. The first part of the case 1 has a generally tubular shape with an upper tubular part 3 on which it is possible to position a connection piece of an engine cooling circuit. Below an outer shoulder 4, there is an annular thickened portion of the element 1 having, under the shoulder 4, a groove housing an 0-ring seal 5. The inner surface of the thickened part then flares outwards and downwards to form a valve seat 6. Farther on in a downwards direction there are two parallel arms 7 each of which has towards its free end an inner notch 8.

The second case part 2 has a more complex shape with an upper opening 9 forming an internal support 10 against which the bottom part of the shoulder 4 is able to bear, this support being followed by a cylindrical part 11 against which the 0-ring 5 can bear, the part 11 continuing downwardly into a kind of housing in which there are a plurality of apertures, in other words two lateral apertures 12, 13 which are directed towards the engine cooling circuit and a bottom aperture 14 which is a bypass for the said circuit. The aperture 15 at the end 3 of the case 1, which receives the connection piece, is intended to communicate with the cooling radiator.

On the inside of the upper part of the case 1 there is a diametral cross member or bridging member 16 having a downwardly open axial lined bore in which, if necessary, it is possible to insert a small metal cup 17. Finally, the bottom part 2 has two support arms 18 which extend from the bottom of the case 2 on either side of the aperture 14, inside the space formed by the arms 7 of the first part of the case, doing so over such a distance that the said end of the arms 18, when the case is in the assembled state, is situated above the bottom end of each of the notches 8.

The thermostatic element 19 is of conventional construction, with a first movable axial member in the form of a rod accommodated in the hole in the cup 17. The body 19 proper being filled with a thermally expansible material such as wax and, in the embodiment shown in Fig. 3, a terminal rod-shaped part 21. A ring 22 of conventional type surrounds the body 19 at the level of a shoulder thereof and carries or forms on its periphery a sealing valve member 23 of elastomeric or metal material, adapted to be applied against the surface 6 of the element 1 under the action of a powerful spring 24. The bottom end of the spring bears against a metal bridging member 25 which forms a cross member with a central passage allowing free translational movement of the body 19 and of its extension 21 which itself - and in a manner likewise known per se - comprises a valve member 26 which is biased downwardly into a position of abutment on the end of the rod 21 by a spring 27 bearing on a shoulder on the body 19 of the thermostatic element. The valve member 26 is intended to cooperate with a surface 28 on the bypass aperture 14.

In the assembled position shown in the drawing, it can be seen that the metal arm or cross member 24 is applied against the ends of the support arms 18 to which it transmits the thrust of the spring 24 so that the arms 18 are subject to a reaction which is orientated downwardly in the direction for longitudinal 1 compression of the arms. The two arms 7 of the element 1 are in this position completely free of the cross member 24 and are not subject to any mechanical bias.

On the other and, in the storage position, in which the two parts 1, 2 of the case are separate, the bridging member 25 is applied by the spring against the bottom face of the notch 8 so that the thermostatic element is entirely contained within and integrated into the first case part 1, fitting of the thermostat according to the invention then requiring only a fitting together of the two case parts and their connection to the various nozzles and connection pieces.

Reference will now be made to Figs. 5 to 8.

This embodiment differs from the previously described embodiment in that the displaceable body 19 of the thermostatic element allows occlusion of the bypass passage 19, not by a flap valve but by a slide valve 29. When it is in the high position, leaving the passage free, this valve is guided outside the passage 14 by radial lugs 30.

In accordance with a preferred feature of the invention, the assembly of the two case elements 1, 2 both in the embodiment of Fig. 1 and in that of Fig. 5, is carried out without the use of screws, which would need reinforcements inserted into the plastics material of the case. For this purpose, when the element 1 and the element 2 have been assembled with an interposed seal 5, a sheet metal ring 31 will be placed in position, its flat upper part 32 bearing against the shoulder 4 to maintain it supported against the shoulder 10 of the other case part, the cylindrical part 33 engaging around the outer surface of the mouth 9 of the case part 2, the part 33 having on its bottom edge a plurality of flanges 34 orientated radially inwardly and adapted to be applied under external radial catches 35 on the case part 2 at the level of the mouth, the said catches having their underside slightly inclined, as is conventional with a bayonet fitting, in order to induce a clamping of the shoulder 4 against the support 10 when the ring is rotated from the insertion position shown in Fig. 7 to the locked position shown in Fig. 8. Once the ring has been turned into this locked position, small internal radial tongues 36-are bent over upwards on either side of the catches 35 so that an accidental rotation of the ring is impossible, the two cases thus being locked together in the assembled state in which the support elements 18 have accepted the loading of the bridging member 25. The metal ring 31 offers a certain elasticity so that while it is playing its part it is able to adapt to local deformations of the case parts due to plastic flow or the like. For dismantling, it is possible to use a special tool and to restore to their initial position, or alternatively break, the small bent-over lugs 36 to allow rotation and then opening of the ring. The assembly formed by the case part 1 and the thermostatic element may be thrown away and replaced by a new assembly which will be fitted onto the case part 2 by means of a new ring.

Reference will now be made to Figs. 9 to 12.

In this embodiment, the two case parts 1, 2 and the thermostatic element are essentially identical to the corresponding parts and elements of the embodiment shown in Fig. 5. However, it can be seen that the mouth portion 9 of the case part 2 has been replaced by a mouth portion 37 of which the upper edge forms the bearing surface 10 against which the inner surface of the support 4 of the case part 1 bears. The mouth portion 37 has on its outer surface screw threads 38 which extend each over a segment of a circle, leaving recessed parts between them. These recessed parts allow the passage of internal teeth 39 on an aluminium nut 40, the upper part of which bears against the shoulder 4. The nut 40 is placed in position of the two previously assembled case parts and, when it is turned, the rapid action screw thread causes a slight lowering of the nut and consequently clamping of the shoulders 4 and 10 against each other. Of course, instead of being made from aluminium or another metal, the nut 40 could be made from a suitably dimensioned plastics material.

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Claims

1. A thermostat of the type comprising a plastics case with a body (1, 2) of generally tubular form and having at least two openings for the inlet and outlet of a fluid, and a thermostatic element (19) capable of expansion under the effect of an increase in temperature, the thermostatic element comprising at least one first fixed part adapted to bear against a support fixed in relation to the case and at least one second movable part adapted to move relative to the first part under the influence of a fluctuation in temperature, and to be restored by a spring (24), characterised in that the case comprises a first part (1) of tubular form in which the thermostatic element (19) is positioned and which has spring retaining means (7) biased in tension by the thrust of the spring, and a second part (2) having support elements (18) adapted to receive the thrust of the spring in a direction tending to compress the said support elements (18), the support elements (18) being designed to accommodate the thrust of the spring when the two parts of the case (1, 2) are assembled and thus to relieve the said retaining means (7) of the biasing of the spring.

2. A thermostat according to Claim 1, characterised in that it comprises a transverse member (25) having two oppositely directed faces, one of which receives the thrust of the spring (24) while the other is applied against the support elements (18) in such a way as to transmit to the support elements the thrust of the spring tending to compress the support elements.

3. A thermostat according to Claim 2, characterised in that the part of the case (1) which does not comprise support elements (18) has elongated arms (7) carrying notches (8) adapted to receive the end of the transverse member (25) against which the spring (24) bears so that the arms (7) are subjected by the spring to a biasing in tension so long as the two parts of the case are not assembled the one to the other, whereas in the assembled state, when the support parts (18) come in contact with the transverse member (25), they raise it and remove the loading from the arms which are thus relieved.

4. A thermostat according to any one of Claims 1 to 3, characterised in that the support elements are arms (18) extending from the second part (2) of the case.

5. A thermostat according to any one of Claims 1 to 4, characterised in that the end of the other movable element (20) of the thermostatic element can be received in a cross member or bridging member (16) moulded into the tubular part of the first part (1) of the case.

6. A thermostat according to any one of Claims 1 to 5, characterised in that one of the case parts (1, 2) comprises a bearing surface against which it is possible to apply another bearing surface on the other part (1, 2) of the case, rapid fixing means retaining the said parts clamped one against the other.

7. A thermostat according to Claim 6, characterised in that the rapid fixing means comprises a screw thread (38) obtained directly by moulding on one of the said case parts and cooperating with a complementary nut (40).

8. A thermostat according to Claim 6, characterised in that the rapid fixing means comprises a ring (33), preferably of metal, capable of being fixed by a bayonet-type fixing thanks to corresponding ramps on one of the said case parts, the said ring comprising one or more tongues (36) adapted to be bent back, when fixing is completed, into a position in which they enter indent parts of the case in order to lock the ring against rotation, the said ring having an elasticity which allows it to adapt itself to possible fluctuations of the said case parts (1, 2) which carry the said bearing surfaces.