EP2659102A1

EP2659102A1 - Thermostat for coolant system

Info

Publication number: EP2659102A1
Application number: EP11854448.5A
Authority: EP
Inventors: Zoltan Kardos; Viktor Berggren
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2010-12-27
Filing date: 2011-12-01
Publication date: 2013-11-06
Also published as: EP2659102A4; SE1051375A1; SE535438C2; CN103282618A; WO2012091658A1; BR112013014749A2; CN103282618B

Abstract

The invention relates to a thermostat (8) for use in coolant- based systems comprising a thermostat disc (9)provided with an outer edge portion (10), a sealing ring (11) against which the disc (9) seals in its fully closed position, and a wax element (12) which regulates the position of the disc (9) on the basis of the coolant's current temperature. The invention is achieved by the edge portion (10) forming a predetermined angle (α) relative to the direction of axial movement of the disc (9), resulting in a gradually larger flow cross-section the more the thermostat (8) opens, and by the edge portion (10) having an extent in height corresponding to at least 50%, preferably 80-85%, of the regulating range (6) of the wax element (12) and/or the thermostat disc (9) in axial directions.

Description

THERMOSTAT FOR COOLANT SYSTEM

TECHNICAL FIELD

The present invention relates to a thermostat for use in coolant systems. The invention relates in particular to thermostats for use in cooling systems for combustion engines in vehicles, e.g. in trucks, and concerns especially the configuration of functional parts of the thermostat with the object of improving its flow characteristics and/or regulating range .

STATE OF THE ART

Vehicles with combustion engines are usually provided with a coolant system intended to lead surplus heat away from the engine to a cooler or radiator situated outside the engine. Controlling the liquid flow through or past the cooler, depending on coolant temperature, usually involves using a thermostat which controls the liquid flow in such a way that if the coolant is too warm the liquid flow is guided through the cooler to give off the surplus heat, and if the coolant is not warm enough the flow is guided past the cooler in a bypass line and back into the engine without having given off heat in the cooler .

A significant problem which commonly occurs is that after a period of use coolers begin to leak coolant and have to be removed and repaired or replaced, which is an expensive operation as well as the standstill which the repair causes to the vehicle owner. The cooler beginning to leak is often due to its many joints and metal parts being subject to great thermal and mechanical stresses during operation. One reason for this is that known thermostats regulate the liquid flow more or less abruptly or jerkily, i.e. when the valve disc moves in axial directions as a result of coolant temperature changes and the thermostat opens/closes, there is a relatively rapid change in the curtain cross-section, i.e. the cross- section which allows liquid to pass the periphery (outer edge) of the thermostat disc, and the coolant flow increases quickly. This leads to rapid temperature changes in the cooler. In cold climates the temperature of the cooler when the thermostat is closed may drop to perhaps -30 degrees Celsius, and when the thermostat opens the cooler is exposed to coolant from the engine block which may perhaps be at +90 degrees Celsius. In addition to the cooler alternately becoming very warm and very cold, causing the metal to expand and contract, the liquid pressure in the cooler also

alternates jerkily in step with the opening and closing of the thermostat. These factors combine to lead to fatigue effects in the structure of the cooler and in its various metal parts.

In coolant systems used in vehicles, the thermostat is often situated near to the engine's coolant outlet, i.e. at a certain distance from the cooler which is generally situated close to the vehicle's air intake/grille. This situation combines with the jerky opening and closing of the thermostat to make it difficult for the cooling system to regulate the coolant temperature gently and maintain an even temperature. A coolant system with an outlet-located thermostat often results in long feedback times for the cooling effect, leading to the thermostat being quite unable to reach a state of equilibrium in which it would operate less intensively, i.e. with fewer openings and closings. The thermostat finds itself quite simply in a self-oscillating state causing a large number of openings and closings which become particularly obvious in cold climates. The thermostat beginning to self- oscillate increases markedly the thermal and mechanical loads on the cooler, leading after a while to problems of mechanical fatigue and leakage. Various solutions have been proposed for improving thermostats so that they regulate the coolant flow more effectively and more gently and thereby minimise the thermal loads in the components of the cooling system.

US3591075 describes for example an improved thermostat which causes the liquid flow to become more even while at the same time minimising the risk of overheating the engine and its oil. This is achieved by substances which are expanded by heat being provided in separate containers in the thermostat which act upon a membrane which itself causes a piston rod to exert a pressure force which moves the thermostat disc.

However, the invention describes primarily a novel type of wax element which better detects the coolant temperature. The invention does not refer to altering the liquid flow through the thermostat or to altering the active regulating range of the thermostat.

US5549244 describes another thermostat with a thermostat disc provided with axial recesses in its edge region with the object of providing one or more small ducts which the coolant can pass through to bypass the thermostat disc. This makes it possible for the flow past the thermostat disc to increase when the thermostat gradually opens. By making stepped changes of the ducts in axial directions it is possible to achieve a stepped increase in the liquid flow, i.e. an increase in more or less distinct stages. A significant disadvantage is that this configuration entails the provision in the thermostat disc of special ducts requiring various precision-made parts such as double-injected plastic parts etc., making the thermostat expensive both to manufacture and to fit. More parts, and parts made of plastic or similar material, also increase the risk of durability problems adversely affecting the service life of the thermostat. Prior art within this field thus does not solve the problem of achieving in a simple way a thermostat which widens the active regulating range and regulates the liquid flow past the thermostat disc more evenly by gradually and progressively opening and closing the liquid flow so that the thermostat reduces the number of necessary openings and closings and can therefore more easily achieve a state of equilibrium which minimises the thermal and mechanical load upon the coolant system and the cooler.

SUMMARY OF THE INVENTION

An object of the invention is to solve the above problem and propose a thermostat with a thermostat disc so configured that the thermostat's regulating range is widened/increased, making it possible for the thermostat to gradually and progressively increase or decrease the liquid flow in response to coolant temperature changes so that it can more easily achieve a state of equilibrium and thereby minimise the number of its

necessary openings and closings, leading to reduction in the thermal and mechanical load upon the cooling system and the cooler .

A further object is that only the configuration, the geometry, of the thermostat disc should need to be altered and that no further parts of the thermostat should need to be altered or added .

A further object of the invention is that it be possible for the thermostat to be fitted in a normal way in existing types of coolant systems and thermostat housings.

A further object of the invention is that the configuration should involve few parts, be functional, achieve long service life and be cost-effective and easy to manufacture, fit and maintain . These and further objects and advantages are achieved

according to the invention by a device defined by the features indicated in the independent claim 1.

The invention thus relates to a thermostat for use in a coolant-based system and particularly in a coolant system in a vehicle, e.g. in a truck. The invention is intended to reduce the number of thermal cycles which the cooling system and the cooler undergo during operation and to improve the

thermostat's operating characteristic, regulating range and performance. The thermostat disc is provided with a

wider/higher and somewhat cone-shaped outer edge or flank which causes the wax element in the thermostat to actively regulate the liquid flow over a larger proportion of the lift height of the thermostat disc and the wax element, thereby reducing the number of openings/closings of the thermostat. The invention also makes it possible for the thermostat to operate with a smaller or small continuous coolant flow, making it easier to reach equilibrium, with consequent positive effects on, for example, the service life of the cooler. The conical shape of the edge of the thermostat disc results in a predetermined angle relative to the direction of axial movement of the disc and hence relative to its sealing ring. The cone angle is preferably about 3 degrees such as to cause small coolant flows at low thermostat lifts and

gradually larger coolant flows at higher/greater thermostat lifts. The cone angle may of course be both greater and smaller depending on the flow characteristic desired in the particular case. With a cone angle of 3 degrees the angle between the edge of the thermostat disc and its notional centreline, i.e. the direction of axial movement of the disc, will be 1.5 degrees.

The configuration according to the invention thus achieves a more gradually increasing liquid flow over a larger proportion of the thermostat lift than with known thermostats, resulting in more even regulation and reducing the number of

openings/closings which the thermostat has to effect.

A further object of the invention is to reduce the liquid flow during more of the opening phase by increasing it

gradually/ slowly in response to rising coolant temperature. The wide edge or flank results in the regulating range being wider and also being within a more advantageous range for the wax element, and in the temperature oscillations becoming smaller in the cooling system. This is achieved without any axial ducts or other similar facilities needing to be adopted and implemented in the thermostat disc. In practical

experiments it has been found that at an ambient temperature of 0 degrees Celsius the number of openings/closings is reduced by about 70% compared with known thermostats on the market .

The edge of the thermostat disc is also configured with a large radius at the top, as seen in cross-section. This helps to achieve gradual opening and hence progressive increase in flow when the thermostat opens to a larger curtain cross- section. The configuration of the thermostat disc according to the invention is advantageous in being easy to make with great precision, e.g. of metal, using similar manufacturing technology which is already currently used in making known thermostat discs.

A further advantage is that the invention does not entail any reconfiguration of outer mechanical parts of the thermostat but only changes to the configuration, the geometry, of one already existing part of the thermostat. The fact that no further parts need be added makes the configuration cost- effective and easier and less expensive to implement and makes it possible to fit the thermostat in a normal way in existing types of coolant systems. Further objects and advantages of the invention are indicated by the more description of the invention set out below and the attached drawings and other claims .

BRIEF LIST OF DRAWINGS

The invention is described below in more detail in the form of some preferred embodiment examples with reference to the attached drawings .

Figure 1 is a cross-section through a thermostat according to prior art.

Figure 2 is a cross-section through a thermostat according to the invention comprising a thermostat disc with a

substantially heightened and somewhat cone-shaped edge portion .

Figure 3a depicts a partial enlargement of a thermostat according to the invention in a fully closed state showing more clearly the association of the thermostat disc with the sealing ring, and the conical shape of the disc.

Figure 3b depicts the partial enlargement according to Figure 3a of the thermostat according to the invention, but with the disc in a somewhat open state resulting in a narrow passage for a small liquid flow.

Figure 3c depicts the partial enlargement according to Figures 3a and b of the thermostat according to the invention, but with the disc in a more open state resulting in a larger passage which allows a larger liquid flow. Figure 3d depicts the partial enlargement according to Figures 3a-c of the thermostat according to the invention but with the disc in an almost fully open state resulting in a large passage and correspondingly large liquid flow.

DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 is a cross-section through a thermostat 1 according to prior art. A thermostat disc 2 abuts against a sealing ring 3 in the thermostat and is regulated in axial directions by means of a wax element 4 provided with a stem 5 movable in axial directions which is also called a pin. When the wax element 4 is warmed by coolant flowing past it, the stem 5 is pushed gradually out from the wax element 4 and exerts a force against the upper yoke 6 of the thermostat, thereby pushing the wax element and the disc 2 downwards in the diagram against the action of a disc spring 7. The thermostat thus opens and allows liquid to flow past the outer circular edge portion of the disc. The low edge height geometry of the disc causes the opening phase to become substantially jerky and quick and the flow velocity of the coolant to increase very abruptly from no flow at all to full flow.

Figure 2 is a cross-section through a thermostat 8 according to the invention. The thermostat disc 9 is provided at its outer periphery with a substantially heightened and somewhat obliquely positioned edge portion 10. The edge portion 10 may for example be formed by pressing the thermostat disc 9 in the same way as is currently done when manufacturing many known thermostat discs, but in the case of the disc 9 the pressing is significantly more pronounced and deeper. The edge portion 10 may of course also be formed in some other way, e.g. by moulding or fitting a separate part on the disc 9. The active regulating range (C) of the thermostat 8 is represented by the height of the edge portion 10 between sealing points, i.e. from the lower point A on the edge portion which seals against the sealing ring 11 in the closed position of the thermostat 8, to the upper point B on the upper surface of the disc's edge portion 10, i.e. where the edge portion makes the transition to a radius R which causes a fully open state of the thermostat 8 in which the liquid flow is no longer reduced by the influence of the disc's edge portion, and amounts to at least 50%, but preferably about 80-85%, of the working or regulating range (C) of the wax element 12 and/or the disc 9 in axial directions. Where the edge portion 10 makes the transition to a radius R the liquid flow increases very markedly and in more or less one step and no real regulation of the flow takes place above this level.

With the object of achieving good regulation of the liquid flow and a possibility of states of equilibrium of the flow through the thermostat 8, the disc 9 in the region of the edge portion 10 is cone-shaped. The disc's edge portion 10 forms by this conical shape a predetermined angle relative to the direction of axial movement of the disc. The cone angle is preferably about 3 degrees such as to result in small coolant flows at low thermostat lifts and gradually greater coolant flows at higher thermostat lifts. The cone angle may of course be both greater and smaller depending on the flow characteristic desired in the particular case, but is

preferably 1-6 degrees . A cone angle of 3 degrees results in an angle a of 1.5 degrees between the sloping edge portion 10 of the disc 9 and the direction of axial movement of the disc. In the diagram the conical shape of the edge portion 10 and the angle a relative to the direction of axial movement of the thermostat disc 9 are exaggerated for the sake of clarity.

Figure 3a is a detail enlargement of the thermostat 8 and more specifically the thermostat disc's edge portion 10 and the connection between the thermostat disc 9 and the sealing ring 11. The thermostat 8 is here in a fully closed state. Figure 3b depicts the partial enlargement according to Figure 3a of the thermostat 8 according to the invention but with the thermostat disc 9 of the wax element 12 pressed somewhat downwards and thereby opening slightly, resulting in a narrow passage which allows a small liquid flow past the disc's edge portion 10.

Figure 3c depicts the same partial enlargement as in Figures 3a and 3b of the thermostat 8 according to the invention but with the disc 9 in a still more open state resulting in a larger passage and a consequently larger liquid flow.

Figure 3d depicts the partial enlargement according to Figures 3a-c of the thermostat 8 according to the invention but with the disc 9 in an almost fully open state resulting in a still larger passage and correspondingly larger liquid flow.

Opening the thermostat 8 further would result in its being fully open and no further scope for increasing the liquid flow .

The above description is primarily intended to facilitate understanding of the invention and is of course not restricted to the embodiments indicated, since other variants of the invention are also possible and conceivable within the scope of the inventive concept and the protective scope of the claims set out below. Thus it is perfectly conceivable that the thermostat 8 according to the invention might be used in industrial applications and a variety of other types of vehicles which use a liquid-based cooling system, e.g.

watercraft, cars, contracting machines etc.

Claims

1. A thermostat (8) for use in coolant-based systems, comprising a thermostat disc (9) provided with an outer edge portion (10), a sealing ring (11) against which the disc (9) seals in its fully closed state, and a wax element (12) which regulates the position of the disc (9) on the basis of the coolant's current temperature,

characterised

in that the edge portion (10) forms a predetermined angle (a) relative to the direction of axial movement of the thermostat disc (9), resulting in a gradually larger flow cross-section the more the thermostat (8) opens, and

that the edge portion (10) has an extent in height

corresponding to at least 50%, preferably 80-85%, of the regulating range (C) of the wax element (12) and/or the thermostat disc (9) in axial directions.

2. A thermostat (8) according to claim 1,

characterised

in that the thermostat disc's edge portion (10) is cone-shaped and forms an angle (a) relative to the direction of axial movement or the notional centreline of the thermostat disc (9) .

3. A thermostat (8) according to claim 1 or 2,

characterised

in that the cone angle of the thermostat disc (9) is 1-6 degrees, preferably 3 degrees.

4. A thermostat (8) according to any one of the foregoing claims ,

characterised

in that the angle (a) of the edge portion (10) relative to the direction of axial movement of the thermostat disc (9) is at least 1 degree but preferably 1.5 degrees.

5. A thermostat (8) according to any one of the foregoing claims ,

characterised

in that the conical shape and the width of the edge portion (10) are arranged to result in gentler regulation and to increase the regulating range (C) of the thermostat (8) .

6. A thermostat (8) according to any one of the foregoing claims ,

characterised

in that the thermostat disc (9) is made of pressed metal.

7. A vehicle provided with a thermostat (8) according to any one of claims 1-6.