Abstract:
A thermostat for an internal combustion engine. The thermostat includes a tube type bypass valve member; a spring to keep said valve member in a closed position and a temperature sensitive actuator to move said valve member to an open position. A flow control element is provided to control a flow of fluid past said valve member as said valve member opens to prevent a sudden cooling of the engine after the engine has already reached an initial warm condition.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to the field of thermostats and more particularly to thermostats of the type used in liquid cooling systems for internal combustion engines. Most particularly, this invention relates to mechanically controlled temperature activated thermostats used to control the flow of coolant through a heat exchanger like a radiator and to methods of use of such thermostats. 
       BACKGROUND OF THE INVENTION 
       [0002]    A thermostat is a temperature activated valve used in internal combustion engines to regulate the flow of liquid coolant. When the thermostat valve is closed, the flow of liquid coolant is prevented from being circulated through a heat exchanger such as a radiator and so the engine is allowed to quickly heat up to its optimum or design operating temperature. The engine recirculation circuit is typically restricted to a small volume of fluid compared to the overall or total volume of the cooling system. When the thermostat valve is opened, coolant from the larger cold volume is permitted into the smaller volume engine recirculating system and passes through the cylinder head where it gets hot. It is then circulated from the engine into a radiator or other heat exchanger where it loses the heat to the air flowing through the radiator. The cooled fluid is then led back to the engine where it can be used to remove further heat from the engine, recirculated to the radiator and so on. A pump driven from the engine propels the coolant around the system. 
         [0003]    This type of thermostat valve typically operates mechanically. Most commonly, a wax pellet is provided inside a sealed chamber. The wax is solid at low temperatures, but as the engine heats up the wax melts and expands. As the wax expands, it pushes an actuator rod outwardly from the chamber that in turn opens the valve. By altering the composition of the wax, the temperature at which the valve opens can be controlled. Typically, such a thermostat valves operate generally in the range of 60° C. to 100° C. and in certain cases may run cooler or even hotter. 
         [0004]    To reduce emissions and pollution, modern engines are designed to run hotter than before, typically over 80° C. and even higher. This permits the engine to operate more efficiently as well. However, a higher operating temperature for the engine creates certain problems for the cooling system in general and the thermostat in particular. In particular, mechanical thermostats are mass-produced as economically as possible. They typically include a stabilizing spring to position the valve components away from the base. This is desirable, because the connection is flexible and will not fatigue and fail like a rigid or fixed joint. When such a device is closed, the parts are anchored somewhat by the contact between the valve and the valve seat. However, when the valve is lifted off the valve seat as the valve opens, then the components that are flexibly attached are freeer to move, leading to vibration and chatter of the valve due to engine vibration and the like. This results in an uncontrolled gap opening between the valve and the valve seat meaning an uncontrolled flow of coolant from the cold side to the warm side through the valve. 
         [0005]    Once the valve opens, there is a rush of cold coolant that floods the engine cooling system and creates a dramatic temperature drop that is hard on the engine components, because of such a flexible or resilient joint. The cold fluid tends to rush in because the thermostat valves are operating in a boisterous environment. The pressures in the cooling system can be large forcing the flow somewhat. The engine itself is typically vibrating and shaking, leading to chatter of the valve as it opens. The valve can be knocked askew by the fluid movement, resulting in a larger opening than intended for that temperature. As a result the thermostat permits large and sudden flows of cold fluid into the engine block when the valve first opens. 
         [0006]    Cold fluid in a hot engine is problematic. For example, this initial drastic change of temperature has been known to cause head gasket failure in certain vehicles. Essentially, the engine heats up quickly as compared to the rest of the system and then the thermostat opens. This permits a sudden, and given the relative volumes a rather sustained rush of cold fluid to enter the head causing a temperature shock to the engine components. This problem is most acute in colder climates on initial start-up, when the coolant outside of the engine recirculation circuit may be at a very low temperature as compared to the engine temperature, due to very cold ambient conditions. 
         [0007]    In addition to being hard on the engine components, such a sudden rush of cold fluid can drastically reduce efficiency and performance of the engine during the duration of the cold flow. As a result, a sudden plume of pollution temporarily surges from the tailpipe or exhaust until the engine and coolant system attain an optimum balance. However, it can take some time for the heat of the engine to warm the larger volume of cold cooling liquid and until it does so the engine is being over cooled and is both inefficient and polluting. 
         [0008]    The problem identified therefore is this sudden rush of coolant into the hot running engine of the vehicle as the valve first opens. One way to address this problem is to have an electronically controlled thermostat, where the degree of opening up thermostat, and thus volume of fluid flow can be precisely controlled. However, such thermostats are extremely expensive and not suitable for most mass production OEM type applications. Another alternative is to try to vary the composition of the wax pellet to cause differential displacement of the piston over the temperature activation range. However, this also is extremely difficult to attain in practice because the expansion of mixed composition wax is not easy to implement or control. It is very difficult, if not impossible to control the rate of opening between the open and closed positions through wax composition changes alone. 
         [0009]    What is needed is a simple and efficient method for controlling the initial inflow of liquid coolant into a hot engine through a mechanically actuated thermostat valve as the valve opens. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides a simple and easy solution to the problem of the sudden rush of liquid coolant into a hot engine as discussed above. In particular, this invention relates to thermostats having tube style valve members that provide a thermostat having an initial or a cold position, in which the valve is closed to the coolant line coming from the radiator. The valve, a tube type valve member, permits generally axial flow through a short and small volume engine recirculation cooling fluid circuit while simultaneously preventing transverse flow from the larger volume radiator cooling circuit. Once the engine temperature is reached, the tube type valve opens and permits a gradual and controlled introduction of the cold side coolant fluids through the valve into the engine. 
         [0011]    The present invention provides a way of configuring the mechanical valve elements to control the initial flow of fluid through the opening of the valve in a way that permits the engine designer to moderate the thermal shock of cold liquid coolant entering an engine at running temperatures. By controlling the flow rates over the initial opening sequence, the present invention permits a gradual introduction of coolant fluid into the engine block, thereby mitigating both thermal shock and the pollution plume. 
         [0012]    Therefore, according to a first aspect of the present invention there is a provided a thermostat for an internal combustion engine, the thermostat comprising: 
         [0013]    a tube type bypass valve member; 
         [0014]    a means to bias said valve member to a closed position; 
         [0015]    a temperature sensitive actuator to move said valve member to an open position against said biasing means; and 
         [0016]    a flow control element to control a flow of fluid past said valve member as said valve member opens. 
         [0017]    According to another aspect of the present invention there is provided a method of controlling a flow of fluid through a thermally activated mechanical thermostat in a vehicle cooling system comprising the steps of: 
         [0018]    providing a tube type valve member having an open top and bottom and a continuous side; 
         [0019]    providing a flow control member adjacent to said valve member; and 
         [0020]    shaping said flow control element to control a flow of fluid past said valve member as said valve member opens. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Reference will now be made to preferred embodiments of the present invention by way of example only as shown in the attached figures. 
           [0022]      FIG. 1  is an example of a prior art tube type valve design; 
           [0023]      FIG. 2  is a view of an embodiment of the present invention in the fully closed position; 
           [0024]      FIG. 3  is a view from above of  FIG. 2 ; 
           [0025]      FIG. 4  is a view of the embodiment of  FIG. 2  in a partially open position; 
           [0026]      FIG. 5  is a view of the embodiment of  FIGS. 2 and 3  in a fully open position; 
           [0027]      FIG. 6  is a view of alternative profiles for the present invention; and 
           [0028]      FIG. 7  is a graph illustrating the effect on fluid flow volume of the profiles of  FIG. 6 ; and 
           [0029]      FIG. 8  is a further embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]      FIG. 1  shows a prior art thermostatic valve  10  in an engine environment  12 . A passageway  14  is connected to the radiator or heat exchanger. A passageway  16  is a short recirculation passageway in the engine itself through which the coolant flows when the thermostat valve  10  is closed as shown in solid outline in  FIG. 1 . The thermostat valve  10  includes a tube-like valve member  18  which allows coolant to circulate in the direction of arrow A up through the valve and into the engine recirculation coolant passageway  16 . Upon the engine warming to the design operating temperature, a thermally activated actuator (not shown) opens the valve  18  in the direction of arrow B to position  20 . At this point, large volumes of coolant indicated by arrow C pass through the valve and change the temperature of the engine. As discussed above, for the first six or seven minutes the cold coolant creates a thermal shock within the engine until the engine has sufficiently warmed the cold liquid coolant in the entire coolant system closer to design operating temperatures. 
         [0031]      FIG. 2  shows a cross-section through an embodiment of the present invention indicated as  22 .  FIG. 2  shows a tube type valve member  30 , similar in form to the valve member  18  of  FIG. 1 . The valve member  30  is attached to a central post  32  by means of a bushing  34  held in place by threaded end cap  36 . A stabilizing spring  38  locates and stabilizes the bushing  34  and the valve member  30  at the end of the central post  32 . The height of the post  32  is adjustable by means of the threaded end cap  36 . A collar  40  is provided on a moving valve frame  42  to center the stabilizing spring  38  on the post  32 . A thermo-mechanical actuator  40  is located at an end of the post  32  opposite to said valve member  30  and contains a sealed chamber having a thermally expanding material such as wax. The wax, when heated melts, expands and extends an actuator piston  42  outwardly. The piston  42  is aligned with post  32 , and moves the entire post  32 , valve member  30  and stabilizer spring  38  assembly upwardly. As the valve member  30  is moved upwardly, it is raised off valve seat  44  and begins to permit fluid from the cold side  46  pass into the hot side  48 . 
         [0032]    A spring or a biasing element  50  is located between an underside of a stationary valve frame  52  and a moving spring housing  54 . The biasing element  50  urges the valve member  30  to a closed position which position is maintained unless the temperature rises sufficiently to cause the thermally expanding wax to expand thereby extending the valve  30  to the position in dotted outline  58  in  FIG. 2 . A rubber gasket  60  is attached to an end of a flange  62  of the valve frame  52  which extends outwardly from the thermal-mechanical actuator as shown. The gasket  60  permits the stationary valve frame  52  to be clamped in place within the engine cooling system in a conventional manner. 
         [0033]      FIG. 3  shows a top view of the valve of  FIG. 2 , showing the bushing  34  and openings  64  through which coolant may pass, and which is why the valve member  30  is characterized as a tube type valve member. Basically it has an open top and bottom to permit flow but continuous sides, to block flow. 
         [0034]    According to the present invention, the thermostat  22  also includes a flow control element  70  ( FIG. 2 ) to control the flow as the valve  30  first opens. The flow control element  70  includes tabs  72 ,  73  that are bent around the stationary valve frame  52  to retain the flow control element  70  in place. In this way the flow control element  70  can be specifically configured for particular operating environments and secured in position on a standard base  52 . Thus, the present invention provides a simple and easy to incorporate element  70  for existing thermostatic valve. It will be understood by those skilled in the art that while the embodiment shown is held in place by bent tabs, many other ways of securing the flow control element  70  to the frame  52  are comprehended including welding or the like. 
         [0035]    The preferred embodiment shows a separate flow control element that is secured onto an existing flange member of a stationary frame of the thermostat. The present invention also comprehends that the flow control element could be integrally formed as part of the stationary frame without departing from the scope of the invention, such as by machining or the like the flow control surface directly out of the stationary frame. In this case although there is no separately attached flow control element, the part of the stationary frame which provides the flow control surface will be equivalent to the flow control element of the present invention. The use of a separate drawn element as shown is believed preferred for cost and ease of manufacture but the invention is not limited thereto. Any structure having a flow control surface will be considered to be within the invention whether by means of two elements or more or fewer elements. 
         [0036]    As can be seen the flow control element  70  includes a flow control surface  74  that diverges from the valve seat  44  onto which a bottom edge  45  of the tube type valve element is seated in a closed position. As the temperature of the coolant rises and the actuator begins to extend the central post  32 , the lower edge  45  of the tube like valve element  30  is displaced upwardly from the valve seat  44 . As can now be appreciated the shape of the flow control surface  74  permits the volume of the flow to be controlled. The amount of divergence between the surface  74  and lower edge of the tube like valve element can be controlled to permit a predefined amount of coolant fluid to pass through the gap at any point in the outward stoke of the actuator. 
         [0037]      FIG. 4  shows the embodiment of  FIG. 3  as the actuator begins to lift the tube type valve member  30  off the seat  44 . As can be seen the stroke of the piston and so the gap between the bottom edge of the valve and the valve seat is a distance a, and yet the opening or gap between the bottom edge of the valve and the flow control surface is distance b. The distance b can be any desired amount as explained below, but will be less than the distance a. The distance b will determine how much cooling fluid will pass into the warm side from the cold side. By changing the shape of the surface  74  the amount of coolant passing from the cold side  46  to the warm side  48  can be varied and controlled at each point of the stroke of the thermally activated actuator. In this manner the flow through the valve  22  can be tailored to suit the specific engine being cooled. 
         [0038]      FIG. 5  shows the embodiment of  FIG. 4  with the coolant at a higher temperature and hence with a greater displacement of the valve element  30  by the actuator off the valve seat  44 . In this Figure the stroke length is shown as distance a 2  and the gap between the flow control surface  74  and the valve element  30  is shown as a distance b 2 . It can be seen that b 2  is less than a 2 . Thus, even at this amount of displacement of the valve element  30  the amount of fluid passing from the cold side  46  to the warm side  48  is restricted as compared to the prior art device of  FIG. 1 . Eventually of course the displacement of the valve element  30  is so great that the full amount of fluid capable of passing through the valve opening begins to pass through and further displacement of the valve element  30  has no further bearing on the flow through volume. Depending upon the circumstances this may or not be reached before the end of the piston stroke when the engine is operating at design running temperatures. 
         [0039]    It can now be understood that a more steeply sloped and higher flow control surface  74  restricts more coolant flow and for longer. Conversely, a less steeply sloped and shorter flow control surface will permit more coolant to flow more quickly. By altering the shape and the height of the flow control surface  74  adjacent to the bottom  45  of the tube like valve element  30 , the initial flow rates of cold side fluid  46  into the warm engine side  48  upon the thermostat valve opening can be carefully controlled. In this manner, the present invention provides a simple and effective means for preventing a sudden surge of cold coolant into the heated engine upon the thermostat first opening. 
         [0040]      FIG. 6  shows four different sample profiles for the flow control surface  74  according to the present invention, shown as A, B, C and D. In each case, the valve element is shown in dashed outline for reference.  FIG. 7  is a schematic plot of stroke displacement against volume of fluid flow, with the points of maximum stroke and maximum flow being marked. The prior art flow pattern, which arises from the configuration of  FIG. 1 , is labelled as well as the flow patterns for the profiles A, B, C, and D. As shown the profile A results in a quick rise in flow volume to a level at  100 , which remains somewhat constant until it again rises quite quickly to full flow at  102 . The profile B shows a slow rise at first with a steeper rise towards full flow at  102 . The profile C shows a quicker rise in flow than profile B at first, but a more gradual rise at the end of the stroke. The profile D shows a very slow rise in the flow volume for the first part of the stroke, followed by a rapid rise in volume at the end. 
         [0041]    While the foregoing examples show particular embodiments it will be understood that many shapes of flow control surface are comprehended by the present invention. It can now be appreciated that the present invention comprehends flow control surfaces that include complex curves, as well as primarily concave and convex curved surfaces. The flow control surface can also be made planar, stepped or any other shape that is desired to provide a particular flow profile over the initial stroke of the thermally activated actuator. The profiles A, B, C and D are examples only, and many other shapes are comprehended by the present invention. What is believed important is to provide a flow control surface  74 , which is sized, shaped and positioned to permit the initial flow of cold fluid from the cold side to be controlled to permit a more gradual and gentle introduction of the cold fluid into the engine than was possible in the prior art tube style mechanical thermostats. 
         [0042]      FIG. 8  shows another embodiment of the present invention in which a flow control element  118  is placed on the cold side  46  of the tube type valve element  30 . In this case the flow control element  118  is incorporated into the rubber gasket  60  and will be held in place by the same clamping action that holds the stationary frame  52  of the valve  22  in place. The flow control surface  130  is defined as the surface between the bottom of the valve element  45  and the flow control element  118 . In  FIG. 8  the flow control element  118  is generally parallel to the side of the valve in cross section. This shape will permit a constant, but modest volume of flow for the first part of the stroke of the actuator, and after that when the valve bottom passes past the top of the element, the gap will open up quite quickly to permit full flow. Again, while a generally straight, in cross section profile is shown, the present invention comprehends any profile as may be suitable for providing a more controlled and preferred introduction of cold fluid into the warm side of the cooling system on initial valve opening. While the cold side positioning of this embodiment is suitable for some applications the warm side positioning of the flow control element of  FIG. 3  is preferred because there is usually physically more space on the warm side than on the cold side in most circumstances. 
         [0043]    Another aspect of the flow control surface can now be appreciated. In the boisterous environment of an engine, the flow control surface also acts as a guide for the valve element to prevent excess displacement, for example by being knocked too far askew by vibrations or fluid pressure. The flow control surface can help to restrict displacement of the valve element as it is being lifted off the valve seat  44  during the warming stage and can help to guide the element back down safely onto the valve seat  44  on the cooling down phase. Thus the present invention also provides for sizing and shaping the flow control element to act as a guide means to guide valve element back onto the valve seat  44 . 
         [0044]    The present invention permits control over the amount or rate of cold fluid being introduced into the engine. Thus, the engine can be kept running hotter sooner than in the prior art, increasing both the efficiency and reducing initial pollution problems. Even though the same amount of coolant is to be heated, the present invention provides for a warm engine at least 20% faster than is possible with the prior art, and perhaps even better than 20% in some cases. 
         [0045]    While reference has been made to preferred embodiments of the invention those skilled in the art will understand that they are provided by way of example only and that various modifications and alterations may be made that do not depart from the broad scope of the claims as attached. For example while various flow control surface profiles are shown other can be made according to suit the individual operating characteristics of a particular engine.