This invention relates to a thermostat assembly and in particular to a thermostat assembly for a cooling circuit of an internal combustion engine.

It is well known to provide a thermostat assembly for the cooling circuit of an internal combustion engine to restrict the flow of cooling water through the radiator when the engine is started from cold.

It has become increasingly popular in recent years to use a combined bypass and thermostat assembly located in the supply between the bottom of the radiator and the circulation pump rather than in the return between the engine and the top of the radiator. This change in practice has been primarily encouraged by the need to more accurately control the coolant temperature of the engine and to eliminate the large temperature oscillations which can occur when a top mounted thermostat is used.

However, it is a problem with such supply line located bypass and thermostat assemblies that they can lead to the thermostat being unduly influenced by the temperature of the relatively cold coolant entering from the bottom of the radiator. In extreme cases this can lead to the thermostat restricting the flow of cold coolant from the radiator to such an extent that boiling

of the coolant within the engine occurs. It is a further problem with such prior art bypass and thermostat assemblies that the unregulated flow regime within the valve chamber can lead to inconsistent operation due to random impingement of hot fluid from the bypass or cold fluid from the radiator upon the temperature sensitive part of the thermostat. It is an object of this invention to overcome the

disadvantages associated with known supply line or

bottom hose bypass and thermostat assemblies.

According to a first aspect of the invention there is

provided a combined bypass and thermostat assembly for a

cooling circuit of an internal combustion engine comprising a housing defining a valve chamber and a bypass and thermostat valve assembly mounted in the

valve chamber, the housing having a first fluid inlet to

connect the valve chamber to a source of cooled fluid, a second fluid inlet to connect the valve chamber to a

bypass flow from the engine and a fluid outlet to connect the valve chamber to a return supply to the

engine, the bypass and thermostat valve assembly having

a temperature responsive valve actuating means connected

to a first valve member to regulate the flow of fluid

from the first inlet to said outlet in response to the

sensed temperature of the fluid in contact with a

temperature sensitive part of said temperature

responsive valve actuating means and a second valve

member to regulate the flow of fluid from said second

inlet to said outlet characterised in that a flow

control means is attached to part of the wall of the

valve chamber to direct the fluid entering the housing

through said second inlet over said temperature

sensitive portion of the temperature responsive valve

actuating means so that the position of the first valve

member is determined primarily by the temperature of the

fluid entering the valve chamber through the second

fluid inlet.

Preferably, the flow control means may include a tube connected to the second inlet to form an inner valve

chamber encircling part of the temperature sensitive

portion of the temperature responsive valve actuating

means.

Advantageously, the first valve member is plate like and

acts so as to deflect flow from the first inlet away from the temperature sensitive portion of the temperature responsive valve actuating means.

The first valve member may be attached to the

temperature sensitive portion of the temperature

responsive valve actuating means so that between 10% and

20% of the outer surface area of the temperature

sensitive portion is exposed to fluid entering through

the first inlet.

The temperature sensitive portion may be a wax filled

temperature responsive actuator.

The housing may comprise of two separate housing parts

connected together to define the valve chamber.

The tube may be formed as an integral part of one of the two housing parts.

According to a second aspect of the invention there is provided a cooling circuit for an internal combustion engine comprising a radiator having a top tank and a bottom tank, a combined bypass and thermostat assembly interposed in the supply between the bottom tank and the engine, a coolant circulation pump to circulate coolant through the engine and return it via a return line to the radiator and a bypass line connected between the return line and the combined bypass and thermostat assembly to allow a controlled flow of coolant from the return line to pass back into the engine wherein the bypass and thermostat assembly comprises of a housing

defining a valve chamber and a bypass and thermostat valve assembly mounted in the valve chamber, the housing having a first fluid inlet to connect the valve chamber to the supply line from the bottom of the radiator, a second fluid inlet to connect the valve chamber to the bypass line and a fluid outlet to connect the valve chamber to the engine, the bypass and thermostat valve assembly having a temperature responsive valve actuating means connected to a first valve member to regulate the flow of fluid from the first inlet to said outlet in response to the sensed temperature of the fluid in contact with a temperature sensitive part of said temperature responsive valve actuating means and a second valve member to regulate the flow of fluid from said second inlet to said outlet, characterised in that a flow control means is attached to part of the wall of the valve chamber to direct the fluid entering the housing through said second inlet over said temperature sensitive portion of the temperature responsive valve actuating means so that the position of the first valve member is determined primarily by the temperature of the fluid entering the valve chamber through the second fluid inlet. Preferably, the flow control means may include a tube

connected to the second inlet to form an inner valve chamber encircling part of the temperature sensitive

portion of the temperature responsive valve actuating

means.

Advantageously, the first valve member is plate like and

acts so as to deflect flow from the first inlet away

from the temperature sensitive portion of the

temperature responsive valve actuating means.

The first valve member may be attached to the

temperature sensitive portion of the temperature

responsive valve actuating means so that between 10% and

20% of the outer surface area of the temperature

sensitive portion is exposed to fluid entering through

the first inlet.

The temperature sensitive portion may be a wax filled

temperature responsive actuator.

The housing may comprise of two separate housing parts

connected together to define the valve chamber.

The tube may be formed as an integral part of one of the

two housing members.

The outlet from the bypass and thermostat assembly may be connected to the inlet side of the coolant circulation pump.

The invention will now be described with reference to the accompanying drawings of which:-

Fig 1: is a cross section through a combined bypass and thermostat assembly according to a first embodiment of the invention showing the thermostat valve in a closed position with the bypass valve fully open; Fig 2: is a cross section similar to that of Figure 1 but showing the thermostat valve partially open;

Fig 3: is a cross section similar to that of Fig 1 but showing a first modification; Fig 4: is a cross section through a combined bypass and thermostat assembly according to a second embodiment of the invention showing the thermostat valve in a closed position and the bypass valve in an open condition; Fig 5: is a schematic drawing of a cooling circuit for an internal combustion engine incorporating a combined bypass and thermostat according to the first embodiment of the invention.

With reference to Figure 5 there is shown an engine 11 having a coolant circulation pump 12, a radiator 13 having a top tank 16 and a bottom tank 17 and a combined bypass and thermostat assembly 14 interposed in the

supply line between the bottom tank 17 and the coolant circulation pump 12.

The bypass and thermostat assembly 14 is connected to the bottom tank 17 of the radiator 13 by means of a bottom hose 18 and to the circulation pump 12 by means of a supply hose 15. The bypass and thermostat assembly is further connected to a top or return hose 10 connecting the engine 11 to the top tank 16 of the radiator 13 by means of a bypass hose 22.

In use the cooling circuit operates as follows, initially, when the engine is cold, the thermostat part of the assembly 14 is in a closed position preventing the passage of coolant from the bottom tank 17 into the engine 11 via the bottom hose 18 and the supply hose 15.

To prevent local overheating of the engine 11 when the thermostat valve is closed the bypass valve part of the assembly is open allowing a controlled flow of coolant from the return hose 10 through the bypass passage 22 to the supply hose 15.

When the temperature of the coolant passing through the bypass and thermostat assembly 14 reaches a predetermined temperature the thermostat part of the assembly 14 is operative to allow coolant to gradually be admitted from the bottom tank 17 through the bottom

hose 18 to mix with the coolant already circulating through the engine 11.

When the engine is at its normal running temperature, coolant passes freely from the bottom tank 17 through the bypass and thermostat assembly 14 and into the circulation pump 12, through cooling passages (not shown) defined within the engine 11 and then back to the top tank 16 via the return hose 10 to be cooled for recirculation from the bottom tank 17.

As the temperature of the coolant approaches the normal running temperature the bypass valve part of the assembly closes so that flow through the bypass hose 22 is effectively shut off ensuring that virtually all of the coolant circulates through the radiator 13 before returning to the engine 11.

With particular reference to Figures 1 and 2 there is shown in greater detail the combined bypass and thermostat assembly 14.

The assembly comprises of first and second plastic housings 25,26 secured together by friction welding defining a valve chamber 20 in which is mounted a combined bypass and thermostat valve assembly 30.

The first plastic housing in the form of a tubular inlet member 25 has a cylindrical outer surface 25A for engagement with the bottom hose 18 and an internal surface which defines a first inlet passage 27 and part of the valve chamber 20.

The second plastic housing 26 has an internal cavity which defines the major portion of the valve chamber 20, a first cylindrical portion defining a second inlet passage 26A to connect the bypass hose 22 to the valve chamber 20 and a second cylindrical portion defining an outlet passage 26B to connect the valve chamber 20 to the supply hose 15. The first and second inlet passages 27,26A are on a common axis whereas the axis of the outlet means 26B is inclined with respect to the common axis of the first and second inlet passages 27,26A.

The bypass and thermostat valve assembly 30 is conventional in construction and comprises of a temperature responsive valve actuating means 31 formed by a temperature sensitive portion in the form of a wax filled body 32, an end cap 35 and a reaction rod 33. The reaction rod 33 extends away from the wax filled body 32 towards the first inlet passage 27 where it abuts against an end plate 34 of the valve assembly 30.

A first valve member 36 is attached to the end cap 35 and the wax filled body 32 near to the end from which

extends the reaction rod 33. The first valve member 36 extends radially outwardly from the wax filled body 32 for co-operation with an inwardly extending lip 40 formed on a flange plate 41 connected to the end plate 34. The first valve member 36 and the extending lip 40 form in combination the thermostat valve part of the valve assembly 30 to regulate the flow of coolant from the first inlet passage 27 to the outlet passage 26B.

The first valve member 36 is biased towards the lip 40 against the action of the valve actuating means 31 by a spring 29 interposed between the first valve member 36 and a reaction plate 28 connected to the end plate 34 by means of a pair of longitudinally extending limbs 28A.

The flange plate 41 is used to support and locate the valve assembly 30 within the valve chamber 20 and is clamped around its outer periphery between the first and second housings 25, 26. A sealing ring 42 is interposed between the first housing 25 and the flange plate 41 to provide a seal between the first and second housings 25,26.

At the end of the bypass and thermostat valve assembly 30 facing the second inlet passage 26A there is formed a spring biased second valve means in the form of a bypass flow valve 50. The bypass flow valve 50 has a valve member 51 for abutment against an end wall 52 of the

second plastic housing 26 to regulate the flow of coolant from the second inlet 26A to the outlet passage 26B.

A flow control means in the form of a tube 38 is attached to the end wall 52 of the second housing member 26 and extends away from the second inlet means 26A to define a cylindrical inner chamber encircling the end portion of the wax filled body 32 of the bypass and thermostat valve assembly 30.

The tube 38 prevents coolant from flowing directly from the second inlet means 26A to the outlet means 26B without passing over the wax filled body 32 and directs coolant entering through the second inlet 26A towards the wax filled body 32. This ensures that the wax filled body 32 is primarily influenced by the temperature of the coolant within the inner chamber formed by the tube 38 and not by the temperature of the coolant entering through the first inlet passage 27.

The first valve member 36 deflects coolant entering the thermostat assembly through the first inlet passage 27 outwardly and away from the temperature sensitive wax filled body 32 which in combination with the tube 38 ensures that it is very difficult for cold coolant entering through the first inlet passage 27 to impinge directly upon the main part of the wax filled body 32.

To further shield the wax filled body 32 from the cold coolant entering the bypass and thermostat assembly 14 through the first inlet 27 a small flow of coolant is allowed to reach the wax filled body 32 from the second inlet 26A even when the valve member 51 is in abutment with the end wall 52.

When the engine 11 has reached its normal running temperature the reaction rod 33 is virtually fully extended causing the first valve member 36 to be fully open and the bypass flow valve 50 is closed thereby restricting the flow of coolant passing between the second inlet 26A and the outlet 26B. The closing of the bypass valve 50 ensures that the majority of the coolant passes through the radiator before being returned to the engine thereby achieving maximum cooling.

With reference to Fig 3 there is shown a combined bypass and thermostat assembly which is in most respects identical to that shown in Fig 1 with the exception that the first valve means 36 is attached to the outer surface of the wax filled body 32 further along the wax filled body 32 towards the bypass valve 50. This modification allows between 10% and 20% of the outer surface of the wax filled body 32 to be exposed to the flow from the first inlet passage 27.

This modification prevents the thermostat from opening too soon when the ambient temperature of the coolant from the radiator is very low thereby allowing the engine to attain a higher temperature before relatively cold coolant is admitted from the radiator which gives improved heater performance during engine warm up.

With reference to figure 4 there is shown a second embodiment of the invention in which the first plastic housing is substantially as described above but in which the second plastic housing is replaced by a number of cavities and passageways formed as an integral part of the cylinder head or cylinder block of the engine.

The bypass and thermostat assembly 214 is in most respects identical to that previously described and also utilises a conventional bypass and thermostat valve assembly 230 located in a valve chamber 220. However, instead of the tube 238 which forms the inner valve chamber being formed as an integral part of one of the housings it is in this case a separate component that is press fitted into a bore 278 in the cylinder head 200 which defines part of the valve chamber 220.

In use coolant will enter the valve chamber 220 from the first inlet 227 which is connected to the radiator or from the second inlet 226A depending on the operating conditions. In either case the coolant returns via the

outlet passage 226B to the coolant circulation pump via a hose (not shown) connected to the pipe connector 226C.

If the bypass valve 251 is closed the majority of coolant from the engine passing along the passageway 279, which is connected to other passageways (not shown) within the engine, will go directly back to the radiator via a hose (not shown) connected to the pipe connector 279A.

Although the invention has been described by way of example with reference to a water cooling circuit for an internal combustion engine it will be appreciated that it could be similarly used in an oil cooling circuit for an internal combustion engine or other fluid cooling systems.

Furthermore it will be appreciated that the invention is not limited to the embodiments specifically described herein for example the first and second housings could be made of any suitable material and the bypass and thermostat assembly could be incorporated into the housing of another component forming part of the cooling circuit such as the circulation pump or part of the radiator.

It will also be appreciated that the tube which forms the inner valve chamber can be formed as an integral part of the housing as described with respect to the

first embodiment or be a separate component as described with respect to the second embodiment.