BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a thermostat device for a cooling system according to the preamble of claim 1.

A conventional cooling system comprises a thermostat sensing the temperature of the coolant in a position upstream of a radiator. The thermostat directs the coolant to the combustion engine without cooling in the radiator when the coolant has a lower temperature than a regulating temperature of the thermostat, and to the radiator for cooling when the coolant has a higher temperature than the regulating temperature. The radiator is a component of the cooling system in which the temperature of the coolant can change rapidly. In a conventional cooling system it takes a relatively long time period before the cooled coolant from the radiator reaches the thermostat. The ability of the cooling system to react rapidly to temperature changes of the coolant in the radiator is therefore low. The slow feedback may lead to what is known as

"temperature cycling", in which the thermostat switches between an open and a closed position during a relatively long time period. Consequently, the radiator may be frequently exposed to large thermal loads, leading to a shorter lifetime.

Heavy vehicles are often equipped with a supplementary brake in the form of a hydraulic retarder. In a conventional hydraulic retarder, an oil is used as working medium. When the retarder is activated, the oil is rapidly heated in the retarder. The oil leaving the retarder is cooled in a retarder cooler by coolant circulating in the cooling system of the vehicle. In another kind of hydraulic retarder, the coolant is used as working medium. In this case, the temperature of the coolant in the cooling system rises even more rapidly when the retarder is activated. SE 532 354 shows a cooling system with a thermostat sensing the temperature of the coolant in a pilot line. The pilot line receives a small part of the coolant flow in an inlet line to the combustion engine. In this case, the thermostat senses the temperature of the coolant just after it has been cooled in the radiator. Thus, a considerably faster feedback is obtained when the coolant undergoes rapid changes in temperature in the cooler. The problem of temperature cycling can be essentially avoided with the aid of such a pilot line. SUMMARY OF THE INVENTION

The object of the present invention is to provide a thermostat device which is compact and includes few components at the same time as it has capacity to distribute the coolant flow to a radiator and a radiator bypass line in view of the coolant temperature in two relevant positions of the cooling system.

This object is achieved by the thermostat device defined in claim 1. The thermostat device comprises a valve body configured to direct the coolant entering the thermostat device to the radiator bypass line or the radiator. The thermostat device comprises a first thermal expansion element sensing the temperature of the coolant in a pilot line. The coolant in the pilot line may have a corresponding temperature as the coolant leaving the radiator. The first thermal expansion element provides a stroke in response to the temperature of the coolant in the pilot line. The thermostat device comprises a second thermal expansion element sensing the temperature of the coolant entering the thermostat device. The coolant entering the thermostat device has a corresponding temperature as the coolant leaving the further object. The second thermal expansion element provides a stroke in response to the temperature of the coolant entering the thermostat device. The thermostat device is designed such that the valve body is moved to a position defined by the thermal expansion element providing the longest stroke. Such a design of the thermostat device makes it is possible to direct coolant to the radiator as soon as the coolant temperature exceeds a too high temperature in one of said two positions in the cooling system. Consequently, temperature changes in the radiator and in the further object can be rapidly indicated and followed by a correspondingly rapid regulation of the valve body. The use of two thermal expansion elements and a common valve body results in a compact design of the thermostat device including few components. According to an embodiment of the invention, the thermal expansion elements are designed to provide a stroke moving the valve body against the action of at least one valve spring. The thermal expansion element may comprise at least one valve spring configured to move the valve body to an initial first position when no stroke is provided by the thermal expansion elements. According to an embodiment of the invention, each thermal expansion element comprises a pushing member, wherein the pushing member of the thermal expansion element providing the longest stroke is designed to come in contact with a contact surface and provide a pushing movement of the valve body. Such a design makes it possible for the thermal expansion element providing the longest stroke to push the valve body from the first position to the second position or to a position located between the first position and the second position. In this case, the pushing member of the thermal expansion element providing the smaller stroke will not come in contact with the contact surface. Thus, the thermal expansion element providing the smaller stroke will not affect at all on the positioning of the valve body.

According to an embodiment of the invention, the pushing members may be designed to come in contact with a respective contact surface located on the same side of the valve body. In this case, the valve body may be plate-shaped. The pushing member in contact with the contact surface of the valve body will define the position of the valve body. Alternatively, the pushing members may be designed to come in contact with a respective contact surface of a movement transmitting member which is connected to the valve body. Such a movement transmitting may be a component of a mechanism transmitting the movement from the thermal expansion elements to valve body.

According to an embodiment of the invention, the thermostat device comprises guiding members configured to define a straight line movement of the valve body. The guiding members prevent turning movements of the valve body. The guiding members make it possible to connect the thermal expansion elements to contact surfaces of the valve body located at a distance from a center of the valve body. The guiding members may comprise a guiding pin centrally arranged on the valve body and a stationary arranged guiding member defining a linear moving path for the guide pin and the valve body. The stationary guiding member may define a linear moving path having the same cross sectional area as the guide pin. In this case, the guide pin is slidably arranged in said linear moving path defined by the stationary guiding member.

According to an embodiment of the invention, each thermal expansion element comprises a sensor member configured to sense the temperature of the coolant and a stroke member configured to provide a stroke resulting in an elongation of the thermal expansion element in relation to the sensed temperature of the coolant. Such thermal expansion elements are able to expand in length in view of the temperature of the coolant. At least one of the thermal expansion elements may comprise a sensor member which is stationary arranged in the thermostat device and a stroke member providing a movement of the valve body. In this case, the sensor member is arranged in a suitable stationary position in the thermostat device in contact with the coolant in the pilot line or in contact with the coolant entering the thermostat device. The stroke member may be provided with a pushing member providing a pushing movement of the valve body. One of the thermal expansion elements may comprise a stroke member which is stationary arranged in the thermostat device and a sensor member configured to provide the movement of the valve body. In this case, the movable sensor member may comprise a pushing member providing a pushing movement of the valve body. The movable sensor member is designed to be in continuous thermal contact with the coolant in the pilot line or the coolant entering the thermostat device.

According to an embodiment of the invention, at least one of the thermal expansion elements comprise a sensor member in the form of a capsule enclosing a material body changing phase at a specific temperature and a stroke member in the form of a piston configured to provide said stroke when said material body changes phase. Such a thermal expansion element may have a conventional design. Such conventional thermal expansion elements are inexpensive and they have a reliable function. The material bodies may be wax materials having suitable phase changing temperatures.

According to an embodiment of the invention, the thermostat device comprises a housing enclosing the thermal expansion elements and the valve body. Such a thermostat device has a compact design and it requires substantially no more space than a conventional thermostat. The housing may comprise a first housing part comprising the coolant inlet and the first coolant outlet, and a second housing part comprising the second coolant outlet, wherein a valve seat defines an opening between said parts and that the valve body is configured to be moved between a closed first position and a fully open second position in relation to said opening. When the valve body is in the closed first position, the entire coolant flow entering the first housing part is directed, via the first coolant outlet, to the radiator bypass line. When the valve body is in the fully open second position, the entire coolant flow entering the first housing part is directed to the second housing part and, via the second coolant outlet, to the radiator. When the valve body is in a partly open position, a part of the coolant flow entering the thermostat device is directed, via the first coolant outlet, to the radiator bypass line. A remaining part of the coolant flow is directed, via the opening in the valve seat, to the second housing part and to the second coolant outlet.

According to an embodiment of the invention, the valve body comprises side walls configured to close the first outlet opening in one of said two positions and the second outlet opening in the other position. Such a valve body may be tubular with open end portion.

The further object to be cooled by the coolant in the cooling system may be a temporarily activated object such as a hydraulic retarder or a retarder cooler for a hydraulic retarder. Such a component may rapidly increase the temperature of the coolant in the cooling system when it is activated. In such a case, the second thermal expansion elements is rapidly heated by the coolant entering the thermostat device whereupon it moves the valve body to the fully open second position such that the entire coolant flow is directed to the radiator.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following preferred embodiments of the invention are described, as examples, with reference to the attached drawings, in which:

Fig. 1 shows a cooling system comprising a thermostat device according to the invention,

Fig. 2a- c shows a first embodiment of the thermostat device and

Fig. 3a- c shows a second embodiment of the thermostat device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 shows a cooling system cooling a combustion engine 2 in a schematically indicated vehicle 1. The coolant is circulated in the cooling system by means of a coolant pump 3. The coolant pump 3 is arranged in an engine inlet line 4 leading coolant to the combustion engine 1. After the coolant has passed through the combustion engine 1 it is led, via an engine outlet line 5, to a further object 6 that can be activated intermittently. Thus the cooling system is used for the cooling of combustion engine 1 and a further object 6. The further object is, exemplified, as a hydraulic retarder 6 using coolant as working medium. Alternatively, a working medium in the form of an oil is used in the hydraulic retarder. In such a case, the coolant cools the working medium in a retarder cooler. The coolant is led from the hydraulic retarder 6, via a retarder outlet line 7, to a thermostat device 8. Depending on the temperature of the coolant, the thermostat device 8 directs the coolant to a radiator bypass line 9 or, via a radiator inlet line 10, to a radiator 11. The radiator bypass line 9 directs the coolant back to the engine inlet line 4 and the coolant pump 3. The radiator 11 is arranged at a front portion of the vehicle 1. Other coolers such as a charge air cooler may be arranged in front of the radiator 11. A cooling fan 12 forces a cooling air stream through the radiator 11. After that the coolant has been cooled in the radiator 11, it is led, via a return line 13, back to the engine inlet line 4 and the coolant pump 3. A pilot line 14 circulates coolant to the thermostat device 8. The pilot line 14 comprises a first pilot line part 14a leading a smaller coolant flow from a position downstream of the coolant pump 3 to the thermostat device 8 and a second pilot line part 14b leading the coolant flow from the thermostat device 8 to a position upstream of the coolant pump 3 in the engine inlet line 4.

Fig 2a- 2c show an embodiment of the thermostat device 8. The thermostat device 8 comprises a housing 15. The housing 15 encloses a valve body 16 which is movably arranged in relation to a valve seat 17. The valve seat 17 defines an opening between a first housing part 15a and a second housing part 15b. The first housing part 15a comprises a coolant inlet 7' receiving coolant from the retarder outlet line 7 and a first coolant outlet 9' leading coolant to the radiator bypass line 9. The second housing part 15b comprises a second coolant outlet 10' leading coolant, via the radiator inlet line

10, to the radiator 11. The housing 15 comprises a separate housing part 15c receiving coolant, via a pilot inlet 14a', from the first pilot line part 14a. The coolant leaving the separate housing part 15c is directed, via a pilot outlet 14b'and the second pilot line part 14b, back to the engine inlet line 4. The valve body 16 comprises a centrally located guide pin 16a and the valve seat 17 comprises a guide member 17a. The guide member 17a defines a linear moving path for the guide pine 16a and the valve body 16 in relation to the valve seat 17. Two valve springs 18 are arranged between the valve body 16 and a respective stationary surface 19 in the valve housing 15. The valve springs 18 act with a spring force on one side of the valve body 16 tending to move the valve body 16 towards a closed first position. The thermostat device 8 comprises a first thermal expansion element 21. The first thermal expansion element 21 comprises a first capsule 21a fixedly arranged in the separate housing part 15c in thermal contact with the coolant flowing through the pilot line 14. The first capsule 21a comprises a closed compartment that is occupied by a first material body having the property that it increases in volume when it melts and passes into liquid phase. The first material body changes phase at a first temperature

Ti. The first thermal expansion element 21 also comprises a first piston 21b. A flexible membrane may be arranged between the first material body and an end of the first piston 21b. The first piston 21b extends through an opening 17b in the guide member 17. The first piston 21b comprises, at an opposite end, a first pushing member 21c. The first pushing member 21c comprises a contact surface to be able to come in contact with a contact surface of the valve body 16. When the first material body in the first capsule 21a is in a solid state the pushing member 21c is at a minimum distance from the stationary arranged first capsule 21a. When the first material body in the first capsule 21a is in a melt state, the pushing member 21c has been moved to a position at a maximum distance from the stationary arranged first capsule 21a.

The thermostat device 8 comprises a second thermal expansion element 22. The second thermal expansion element 22 comprises a second capsule 22a and a second piston 22b. The second capsule 22a is arranged in thermal contact with the coolant in the first housing part 15a. The second capsule 22a comprises a closed compartment that is occupied by a second material body. The second material body has the property that it increases in volume when it melts and passes into liquid phase. The second material body changes phase at a second temperature T ₂ . A flexible membrane may be arranged between the second material body 22a and an end of the second piston 22b. An opposite end of the second piston 22b comprises a fixed connection 22e to a stationary component in the housing 15. In this case, the stationary component is the guide member 17a. The second capsule 22a comprises a first part 22c having a larger cross section area than a through hole 16b in the valve body 16 and a second part 22d having a smaller cross section area than the through hole 16b in the valve body 16. When the second material body in the second capsule 22a is in a solid state the second capsule 22a is at a minimum distance from the fixed connection 22e to the guide member 17a. When the second material body in the second capsule 22a is in a melt state the second capsule 22a is at a maximum distance from the fixed connection 22e to the guide member 17a.

The coolant is circulated through the cooling circuit by means of the coolant pump 3 when the combustion engine is in operation. The first capsule 21 is in thermal contact with coolant flowing through the pilot line 14 and the second capsule 22 is in thermal contact with the coolant entering the first housing part 15a via the coolant inlet 7' . As a result, the thermostat device 8 is controlled by the temperature of the coolant in two positions of the cooling system namely in a position downstream of the radiator 11 and in a position downstream of the retarder 6.

During a first operating condition when the coolant in the pilot line 14 has a lower temperature than the first phase changing temperature Ti and the coolant in the retarder outlet line 7 has a lower temperature than the second phase changing temperature T ₂ , the first material body in the first capsule 21a as well as the second material body in the second capsule 22a are in solid phase. Thus, the first thermal expansion element 21 as well as the second thermal expansion element 22 are in non-elongated state.

Consequently, the valve springs 19 maintains the valve body 16 in the closed first position, which is shown in Fig. 2a. When the valve body 16 is in the closed first position there is no cooling demand of the coolant. The entire coolant flow entering the first housing part 15a, via the coolant inlet 7', is directed, via the first coolant outlet 9', to the radiator bypass line 9.

During a second operating condition when the coolant in the pilot line 14 has a higher temperature than the first phase changing temperature Ti and the coolant in the retarder outlet line 7 has a lower temperature than the second phase changing temperature T ₂ , the first material body in the first capsule 21a is in liquid phase and the second material body in the second capsule 22a is in solid phase. In this case, the first material body has provided a stroke of the first piston 21b at which the pushing member 21c has pushed the valve body 16 to a fully open second position against the action of the valve springs 18 which is shown in Fig. 2b. It is to be noted that the movement of the valve body 16 from the closed first position to the fully open second position is not counteracted by the second thermal expansion element 22 since the second part 22d of the second capsule 22a has a smaller cross section area than the through hole 16b in the valve body 16. The pushing member 21c acts on a contact surface of the valve body 16 located at a distance from a center of the valve body 16. However, the guide member 17 and the guide pin 16a ensures that the valve body 16 obtains a linear movement between the closed first position and the fully open second position. In the fully open second position the valve body 16 exposes the opening between the first housing part 15a and the second housing part 15b in an optimal manner at the same time as it closes the first coolant outlet 9' to the radiator bypass line 9. Consequently, the entire coolant flow entering the first housing part 15a via the coolant inlet 7' flows, via the opening, to the second housing part 15b and via the second coolant outlet 10', to the radiator 11.

During a third operating condition when the coolant in the pilot line 14 has a lower temperature than the first phase changing temperature Ti and the coolant in the retarder outlet line 7 has a higher temperature than the second phase changing temperature T ₂ , the first material body in the first capsule 21a is in solid phase and the second material body in the second capsule 22a is in liquid phase. In this case, the second material body has provided a stroke of the second piston 22b at which the first part 22c of the second capsule 22a has pushed the valve body 16 to a fully open second position against the action of the valve springs 18 which is shown in Fig. 2c. It is to be noted that the movement of the valve body 16 from the closed first position to the fully open second position is not counteracted by the first thermal expansion element 21 since the pushing member 21c is not fixedly attached to the valve body 16. Since the first part of 22c of the second capsule 22a has a larger diameter than the than the hole 16b through the valve body 16, it constitutes a second pushing member acting on the valve body 16. The second pushing member 22c acts on a contact surface the valve body 16 located at a distance from a center of the valve body 16. Also in this case, the guide member 17 and the guide pin 16a ensure that the valve body 16 obtains a linear movement between the closed first position and the fully open second position. In the fully open second position the valve body 16 exposes the opening between the first housing part 15a and the second housing part 15b at the same time as it closes the first coolant outlet 9' to the radiator bypass line 9. Consequently, the entire coolant flow entering the first housing part 15a flows, via the opening, to the second housing part 15b and via the second coolant outlet 10', to the radiator 11. During a fourth operating condition when the material body in one of the capsules 21a, 22a has started to melt, the actual thermal expansion element 21, 22 provides a stroke moving the valve body 16 to a more or less open position. In this case, a part of the coolant flow entering the first housing part 15a is directed to the bypass line 9, via the first coolant outlet 9' . A remaining part of the coolant flow entering the first housing part 15a is directed, via the opening, to the second housing part 15b and, via the second coolant outlet 10', to the radiator 11. During all operating conditions, the position of the valve body 16 is defined by the thermal expansion element 21, 22 providing the longest stroke. The first thermal expansion element 21 ensures a fast feedback of the thermostat device 8 when the coolant undergoes rapid temperature changes in the radiator 11. The second thermal expansion element 22 ensures a fast feedback of the thermostat device 8 when the coolant undergoes rapid temperature changes in the retarder 6. The first material body in the first capsule 21a may have a phase changing temperature of about 89°C and the second material body in the second capsule 22a may have a phase changing temperature of about 96°C. The material bodies may be wax materials having suitable phase changing temperatures.

Fig 3a-c show an alternative embodiment of the thermostat device 8. The thermostat device 8 comprises a housing 15. The housing 15 comprises a coolant inlet 7' receiving coolant from the retarder outlet line 7, a first coolant outlet 9' directing coolant to the radiator bypass line 9 and a second coolant outlet 10' directing coolant, via the radiator inlet line 10, to the radiator 11. The housing 15 comprises a separate housing part 15c receiving coolant, via a pilot inlet 14a', from the first pilot line part 14a. The separate housing part 15c comprises a first thermal expansion element 21. The first thermal expansion element 21 comprises a first capsule 21a and a first piston 21b. The first capsule 21a is fixedly arranged in the separate housing part 15c in thermal contact with the coolant flowing through the pilot line 14. The first capsule 21a comprises a closed compartment that is occupied by a first material body having the property that it increases in volume when it melts and passes into liquid phase. The first material body changes phase at a first temperature Ti. The first piston 21b provides a stroke when the first material body melts and passes into liquid phase. The housing 15 comprises a second thermal expansion element 22. The second thermal expansion element 22 comprises a second capsule 22a and a second piston 22b. The second capsule 22a is fixedly arranged in the housing 15 via a fixedly arranged support plate 23. The second capsule 22a is arranged in thermal contact with the coolant entering the housing part 15 via the inlet opening 7' . The second capsule 22a comprises a closed compartment that is occupied by a second material body. The second material body has the property that it increases in volume when it melts and passes into liquid phase. The second material body changes phase at a second temperature T ₂ . The second piston 22b provides a stroke when the second material body melts and passes into liquid phase. In this case, the housing 15 encloses a valve body in the form of a tubular valve body 24, which is movably arranged between a first position which is shown in Fig. 3a, and a second position, which is shown in Figs. 3b, 3c. The tubular valve body 24 comprises a periphery wall 24a, a completely open upper portion and a partly open bottom portion 24b. A support member 25 is arranged on the bottom portion 24b of the tubular valve member 24. The support member 25 comprises an elongated recess configured to receive the second piston 22b of the second thermal expansion element 22. A first spring 26 is arranged between a contact surface of the support member 25 and a spring seat member 27. The first spring 26 acts with a force on the spring seat member 27 such that it will be in continuous contact with a lower portion of a movement transmitting member 28. The first spring 26 provides a resilient connection between the movement transmitting member 28 and the valve body 24. A second spring 29 is arranged between an upper portion of the movement transmitting member 28 and the fixedly arranged support plate 23. The second spring 29 is arranged around the second capsule 22a.

The first thermal expansion element 21 comprises a first piston 21b provided with a first pushing member 21c at an outer end. The first pushing member 21c is able to come in contact with a first contact surface of an upper portion of the movement transmitting element 28. Alternatively, the pushing member 21c is fixedly arranged on the movement transmitting member 28. In this case, an outer end of the first piston can be moved into contact with the pushing member 21c. When the first material body in the first capsule 21a is in a solid state the pushing member 21c is at a minimum distance from the stationary arranged first capsule 21a. When the first material body in the first capsule 21a is in a melt state, the first piston has provided a stroke at which the pushing member 21c has been moved to a position at a maximum distance from the stationary arranged first capsule 21a. The second thermal expansion element 22 comprises a second piston 22b, provided with a second pushing member 22c at an intermediate portion. The second pushing member 22c is able to come in contact with a second contact surface of the movement transmitting element 28. When the second material body in the second capsule 21a is in a solid state the pushing member 22c is at a minimum distance from the stationary arranged second capsule 22a. When the second material body in the second capsule 22a is in a melt state, the second piston has provided a stroke at which the second pushing member 22c has been moved to a position at a maximum distance from the stationary arranged second capsule 22a.

The coolant is circulated through the cooling circuit by means of the coolant pump 3 during operation of the combustion engine 2. The first capsule 21 is in thermal contact with coolant flowing through the pilot line 14 and the second capsule 22 is in thermal contact with the coolant entering the housing 15 via the coolant inlet 7' . As a result, the thermostat device 8 is controlled by the temperature of the coolant in two positions of the cooling system namely in a position downstream of the radiator 11 and in a position downstream of the retarder 6. During a first operating condition when the coolant in the pilot line 14 has a lower temperature than the first phase changing temperature Ti and the coolant in the retarder outlet line 7 has a lower temperature than the second phase changing temperature T ₂ , the first material body in the first capsule 21a as well as the second material body in the second capsule 22a are in solid phase. Thus, the first thermal expansion element 21 as well as the second thermal expansion element 22 are in a non-elongated state.

Consequently, none of the pistons 21b, 22b has provided a stroke at which the pushing members 21c, 22c have provided a pushing movement of the tubular valve body 24 from a first position via the movement transmitting member 28. When the valve body 24 is in the first position, the side walls 24 closes the second outlet opening 10' . In this case, the coolant flows entering the housing 15 is led, via the partly opened bottom portion 24b of the valve body 24, to the first coolant outlet 9' and the radiator bypass line 9. During a second operating condition when the coolant in the pilot line 14 has a higher temperature than the first phase changing temperature Ti and the coolant in the retarder outlet line 7 has a lower temperature than the second phase changing temperature T ₂ , the first material body in the first capsule 21a is in liquid phase and the second material body in the second capsule 22a is in solid phase. In this case, the first piston 21b has provided a stroke at which the first pushing member 21c has pushed the movement transmitting member 28 and the tubular valve body 24 to a second position against the action of the second spring 29 which is shown in Fig. 3b. It is to be noted that this movement of the tubular valve body 24 is not counteracted by the second thermal expansion element 22. Since the second material body is in a solid state, the second piston 22b and the second pushing member 22c is maintained in its initial positions. Since the movement transmitting member 28 has been moved from its initial position by the first piston 21b, the second pushing member 22c is at a distance from the second contact surface of the movement transmitting member 28. In the second position the side walls 24a of the tubular valve body 24 closes the first outlet opening 9' . In this case, the coolant flows, via the second coolant outlet 10', to the radiator inlet line 10. During a third operating condition when the coolant in the pilot line 14 has a lower temperature than the first phase changing temperature Ti and the coolant in the retarder outlet line 7 has a higher temperature than the second phase changing temperature T ₂ , the first material body in the first capsule 21a is in solid phase and the second material body in the second capsule 22a is in liquid phase. In this case, the second piston 22b has provided a stroke at which the second pushing member 22c has pushed the movement transmitting member 28 and the tubular valve body 24 to the second position against the action of the second spring 29 which is shown in Fig. 3c. It is to be noted that the movement of the tubular valve body 24 from the first position to the second position is not counteracted by the first thermal expansion element 21. Since the first material body is in a solid state, the first piston 21b and the first pushing member 21c is maintained in its initial positions. Since the movement transmitting member 28 has been moved from its initial position by the second pushing member 22c, the first pushing member 21c is at a distance from the first contact surface of the movement transmitting member 28. In the second position the side walls 24a of the tubular valve body 24 closes the first outlet opening 9' . Also in this case, the coolant flows, via the second coolant outlet 10', to the radiator inlet line 10.

During a fourth operating condition when the material body in one of the capsules 21a, 22a has started to melt, the actual thermal expansion element 21, 22 provides a stroke moving the valve body 16 to a more or less open position. In this case, a part of the coolant flow entering the first housing part 15a is directed to the bypass line 9, via the first coolant outlet 9' a remaining part of the coolant flow entering the housing 15 is directed, via the second coolant outlet 10', to the radiator 11. Also in this case, the position of the valve body 24 is defined by the thermal expansion element 21, 22 providing the longest stroke.

The invention is not in any way limited to the embodiment that has been described in the drawings: it can be freely varied within the scope of the patent claims.