GB2086536A

GB2086536A - Thermostat assembly

Info

Publication number: GB2086536A
Application number: GB8034691A
Authority: GB
Original assignee: Western Thomson Controls Ltd; Ford Motor Co Ltd; Ford Motor Co
Current assignee: Western Thomson Controls Ltd; Ford Motor Co Ltd; Ford Motor Co
Priority date: 1980-10-28
Filing date: 1980-10-28
Publication date: 1982-05-12

Abstract

A thermostat assembly for a liquid cooling system of an internal combustion engine comprises a valve member (10) movable between open and closed positions by control means which includes a temperature sensitive element, e.g. a body (17) of wax acting between a reaction member (18) and the valve member (10), and a vacuum motor (25) operable in response to changes in engine load as indicated by inlet manifold pressure changes which moves the reaction member (18) in a direction to cause further opening of the valve member, thereby avoiding fluctuations in temperature of the coolant under high engine loadings. <IMAGE>

Description

SPECIFICATION Thermostat assembly This invention relates to thermostat assemblies for liquid cooling systems of internal combustion engines.

Conventional thermostat assemblies for such cooling systems comprise a valve member and a temperature sensitive element, for example, a body of material having a high positive coefficient of thermal expansion, e.g. paraffin wax, which acts between the valve member and a fixed reaction member to move the valve member in response to increases in temperature. The position of the reaction member relative to the valve member determines the temperature above which the temperature sensitive element moves the valve member to allow coolant to flow through the thermostat assembly.

The reaction member is normally adjusted so that, when the engine is started from cold, the valve member is in a closed position, thereby preventing circulation of the liquid coolant and allowing the engine to reach its normal operating temperature quickly. This arrangement however causes the operating temperature of the engine to vary with the load on the engine. This occurs because, under high load conditions, additional heat is generated in the engine as a result of combustion of high quantities of fuel for a given engine speed, and the thermostat assembly prevents additional coolant from circulating through the engine to remove the excess heat.

Additional coolant can only be supplied to the engine when the coolant temperature has risen sufficiently to cause the temperature sensitive element to open the thermostat valve further.

According to the present invention there is provided a thermostat assembly for a liquid cooling system of an internal combustion engine comprising a valve member movable between open and closed positions and control means for moving the valve member between the open and closed positions in response to variations in temperature of the engine coolant, characterised in that the control means also moves the valve member in response to variations in engine load.

By varying the position of the valve member in accordance with engine load, as well as in accordance with engine coolant temperature, the valve member may be opened more widely under high engine load conditions, thereby permitting the additional heat to be removed from the engine. Rapid fluctuations in engine temperature are therefore avoided during both normal running and warm-up of the engine.

The control means is conveniently constituted by a temperature sensitive element acting between a reaction member and the valve member, and means operable in response to variations in engine load for moving the reaction member relative to the valve member.

The temperature sensitive element may be of any suitable construction for example, bellows filled with fluid which expands and contracts the bellows in response to temperature changes.

In the preferred embodiment of the invention the reaction member comprises a pin which is engagable with an abutment formed in the valve member, and the temperature sensitive element comprises a body of temperature sensitive material which alters the position of the abutment relative to the reaction member.

The engine load is preferably detected by a vacuum operated motor adapted for connection to the inlet manifold of the engine, but other engine load detectors may be used. Any suitable linkage may be used to connect the vacuum operated motor to the reaction member, for example a cam arrangement or, preferably, a linkage including a simple pivoted lever.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying schematic drawing, which is a cross section through a thermostat assembly in accordance with the invention.

Referring to the drawing, a thermostat assembly for a water-cooled internal combustion engine comprising a valve assembly 1 mounted in a housing 2 which connects the cylinder head of the engine to a radiator (not shown) via a passage 5.

The valve assembly 1 comprises a body 6 having a flange 7, by means of which the assembly is secured in the passage 5, a valve seat 8 and a supporting ring 9. A valve member 10 having a hollow stem 11 is mounted centrally within the body 6 for axial movement between a closed position, illustrated in the drawing, in which it lies in sealing engagement with the valve seat 8, and an open position in which the valve member is displaced to the right as seen on the drawing, allowing water to pass through the valve assembly. The valve member 10 carries a secondary valve member 12 which seals a bipass passage 13 in the housing 2 when the valve member 10 is in its fully open position. The bipass passage allows coolant to circulate in the engine cooling passages when the valve assembly 1 is closed.A compression spring 14 acting between the valve member 10 and the supporting ring 9 of the body 6 biases the valve member 10 into its closed position.

Aflexible sheath 15 defining a central axial recess 16 is mounted within the hollow stem 11 of the valve member 10, and the space between the sheath 15 and the internal walls of the hollow stem 11 is filled with a body 17 of microcrystalline paraffin wax. The recess 16 houses a reaction pin 18 which is tapered at one end to conform to the internal shape of the recess 16. The other end of the pin 18 is secured to a coaxial rod 19 mounted for axial sliding movement in the housing 2. Reciprocation of the rod 19 and pin 18 is effected by a lever 20 which pivotally mounted at one end to a bracket 21 carried by the housing 2 and articulated to the rod 19 by a ball connection 22.

The other end of the lever 20 is connected to a vacuum motor 25 which is also mounted on the bracket 21. The vacuum motor 25 comprises a vacuum chamber 30 adapted for connection along a vacuum pipe 31 to the engine inlet manifold, a piston 32 slidable within the chamber 32 and sealed to the inner walls thereof by a diaphragm 33, a spring 34 biasing the piston 32 to one end of the chamber 32, and a piston rod 35 connecting the piston to the lever 20.

The operation of the assembly is as follows. In the drawing, the assembly is illustrated in the configuration which it occupies when the engine is running under a low load with cold engine coolant. In this condition, the vacuum manifold pressure is high.

Hence, the piston 32 of the vacuum motor 25 is displaced to the left, as seen in the drawing, against the bias of the spring 34. The rod 19 and pin 18 are therefore fully withdrawn away from the end of the recess 16 in the sheath 15. Since the engine water temperature is low, the body of wax 17 exerts no force between the pin 18 and the valve member 10, thus allowing the compression spring 14to keep the valve member in the closed position and the secondary valve member 12 in the open position. Coolant can therefor only circulate within the engine through the bipass passage 13.

As the water temperature increases the body of wax 17 expands, constricting the recess 16 and bringing the constricted end of the recess 16 into abutment with the tapered end of the pin 18 thereby forcing the valve member 10 away from the pin 18 towards its open position. At the same time, the secondary valve member 12 is closed.

If the engine load should increase, additional heat will be released in the engine. At the same time, the pressure in the inlet manifold will increase, allowing the spring 34 in the vacuum motor 25 to move the piston 32 to the right as shown in the drawings. The rod 19 and pin 18 are thereby displaced to the right, which in turn move the valve member further towards its fully open position. Additional water can therefore flow through the valve assembly, thus removing the additional heat generated by the engine under high load conditions without causing an undesirably large fluctuation in the temperature ofthe engine.

When the high load is removed from the engine, the manifold pressure will decrease so that the rod 18 and pin 19 are moved to the left as seen in the drawing, returning the valve member 10 to the position determined by the state of expansion of the body 17 of wax.

Claims

1. A thermostat assembly for a liquid cooling system of an internal combustion engine comprising a valve member movable between open and closed positions and control means for moving the valve member between the open and closed positions in response to variations in temperature of the engine coolant, characterised in that the control means also moves the valve member in response to variations in engine load.

2. An assembly according to Claim 1 wherein the control means comprises a temperature sensitive element acting between a reaction member and the valve member, and means operable in response to variations in engine load for moving the reaction member relative to the valve member.

3. An assembly according to Claim 2 wherein the reaction member comprises a pin which is engagable with an abutment formed in the valve member, and the temperature sensitive element comprises a body of temperature sensitive material which alters the position of the abutment relative to the reaction member.

4. An assembly according to Claim 2 and Claim 3 wherein the control means comprises a vacuumoperated motor adapted for connection to an inlet manifold of the engine and arranged to move the reaction member in response to variations in inlet manifold pressure.

5. An assembly according to Claim 4 wherein the vacuum-operated motor is operably connected to the reaction member by a linkage including a pivotable lever.

6. A thermostat assembly substantially as hereinbefore described, and as illustrated in the drawings.

7. An internal combustion engine comprising a liquid cooling system which incorporates a thermostat assembly according to any one of Claims 1 to 6.