Abstract:
An expansion tank ( 10 ) for a vehicle cooling system ( 18 ) of an engine using a liquid coolant ( 16 ) includes a tank body ( 12 ) defining a first volume (V 1 ) containing coolant ( 16 ), wherein the coolant defines a variable coolant elevation level (CEL) within the tank body. The tank body ( 12 ) also defines an upper volume ( 20 ) containing air. A bladder ( 14 ) is disposed in the tank body ( 12 ) and defines a second volume (V 2 ) containing air. The bladder ( 14 ) includes a flexible membrane ( 36 ) actuated by an actuator ( 46 ). When the engine is stopped or is below a predetermined temperature, the flexible membrane ( 36 ) is moveable to a first position (FP) which lowers the coolant elevation level (CEL), and when the engine is started or reaches a predetermined temperature, the flexible membrane ( 36 ) is moveable to a second position (SP) which raises the coolant elevation level. A communicating line ( 38 ) is in fluid communication between the upper volume ( 20 ) and the second volume (V 2 ) to fluidly communicate air therebetween.

Description:
BACKGROUND 
       [0001]    Embodiments described herein generally relate to vehicle cooling systems. More specifically, embodiments described herein relate to an expansion tank of a vehicle cooling system. 
         [0002]    Typically an expansion tank of a vehicle cooling system is elevated relative to the other components of the cooling system such that the expansion tank can provide good coolant communicating and cooling system pressure. Communicating of the cooling system removes air or other gases that are trapped or generated in and by the cooling system through the vent lines connected to the tank. In some conventional cooling systems, the “low fluid level line” of the expansion tank is above the engine/vehicle coolant fill level line. Typically, an air volume in a conventional expansion tank is located entirely above the coolant level. 
         [0003]    Due to engine packaging constraints, the low fluid level line of the expansion tank may not be located entirely above the coolant fill level line of the engine. In some cases, the expansion tank may be mounted at a relatively lower position where the level of coolant in the expansion tank may fall below the coolant fill level line of the engine. 
       SUMMARY OF THE INVENTION 
       [0004]    An expansion tank for a vehicle cooling system of an engine using a liquid coolant includes a tank body defining a first volume containing coolant, where the coolant defines a variable coolant elevation level within the tank body. The tank body also defines an upper volume containing air. A bladder is disposed in the tank body and defines a second volume containing air. The bladder includes a flexible membrane actuated by an actuator. When the engine is stopped or is below a predetermined temperature, the flexible membrane is moveable to a first position which lowers the coolant elevation level, and when the engine is started or reaches a predetermined temperature, the flexible membrane is moveable to a second position which raises the coolant elevation level. A communicating line is in fluid communication between the upper volume and the second volume to fluidly communicate air therebetween. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a schematic of an expansion tank for a vehicle cooling system. 
           [0006]      FIG. 2  is a schematic of a second embodiment of expansion tank for the vehicle cooling system. 
           [0007]      FIG. 3  is a schematic of a first temperature activated actuator. 
           [0008]      FIG. 4  is a schematic of a second temperature activated actuator. 
           [0009]      FIG. 5  is a schematic of an electrically activated actuator. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Referring now to  FIG. 1 , a first embodiment of an expansion tank is indicated generally at  10  and has a tank body  12  with a first volume V 1 , and a bladder  14  disposed in the tank body  12  and having a second volume V 2 . The tank body  12  is generally cylindrical, however other shapes and configurations are possible. The first volume V 1  is configured to receive liquid coolant  16  of a cooling system  18 . The cooling system  18  is associated with an engine (not shown) that has a coolant fill level (CFL) and a maximum coolant elevation (MCE). 
         [0011]    The coolant  16  inside the expansion tank  10  forms a coolant elevation level (CEL) within the tank body  12 , and is dependent upon the amount of coolant and the thermal expansion of the coolant. As will be discussed below, the CEL is also dependent on the bladder  14 . During operation of the cooling system  18 , the CEL needs to be at least as high in elevation as the CFL of the vehicle. 
         [0012]    The second volume V 2  in the bladder  14  is configured to be filled with air and coolant vapors, collectively referred herein as “air”. An upper volume  20  is located above the CEL and is also filled with air. The volume in the upper volume  20  and the second volume V 2  is variable as the CEL moves up and down. The first volume V 1  of coolant  16  is the total volume of the expansion tank  10 , minus the second volume V 2  of the bladder, and minus the upper volume  20 . The first volume V 1  of coolant  16  remains about the same. The volume of air contained in the second volume V 2  and the upper volume  20  change relative to each other as the second volume V 2  and the upper volume  20  are in fluid communication with each other. 
         [0013]    A coolant cap  22  is disposed on a top surface  24  of the tank body  12 . The coolant cap  22  is removable to fill the first volume V 1  with coolant  16 . A coolant output  26  is disposed at a bottom surface  28  of the tank body  12  to fluidly communicate coolant  16  to the cooling system  18 . One or more coolant inputs  30  fluidly communicate the coolant  16  from the cooling system  18  to the tank body  12 . 
         [0014]    Typically, the air volume of a conventional tank is located entirely above the CEL. In the expansion tank  10 , at least a portion of the second volume V 2  of air is at a lower elevation than the CEL to displace the CEL in either the “Up” or “Down” direction indicated in  FIG. 1 . 
         [0015]    At least a portion of the bladder  14  is located beneath the CEL. In the expansion tank  10 , at least a portion of the bladder  14  is located at a lower half portion  32  of the tank body  12  such that air is located beneath the CEL. Further, at least a portion of the bladder  14  may be located at the bottom surface  28  of the tank body  12  so that air is at least as low in elevation as the CEL when any amount of coolant  16  is present in the tank body. It is also possible that the bladder  14  can be located at least partially remotely from the tank  10 . 
         [0016]    The bladder  14  may have at least one rigid wall  34  and at least one flexible membrane  36  that is operable to change the volume V 2  of air. In the expansion tank  10 , the bladder  14  is located at the bottom surface  28  of the tank body  12 , the flexible membrane  36  has a generally vertical orientation, and the rigid wall  34  has a generally horizontal orientation, however other configurations of bladder  14  are possible. It should be appreciated that the bladder  14  can have a variety of locations and configurations that elevate the CEL. 
         [0017]    Referring to  FIG. 3  to  FIG. 5 , an actuator  46  actuates the flexible membrane  36 . The actuator  46  can be temperature activated, for example a t-stat (Vax) actuator  48  or a bimetallic actuator  50 , or can be electrically actuated, for example an electro-active elastomer membrane  52 . A mechanical actuator  46 , such as a piston, may also actuate the flexible membrane  36 . 
         [0018]    When the engine is off, the membrane  36  has a first position, shown in dashed as FP, and having a generally convex shape with respect to the interior of the bladder  14 . In position FP, the second volume V 2  of air is decreased and the upper volume  20  of air is increased. 
         [0019]    When the engine starts, or alternatively, when the engine starts and warms up to a predetermined temperature, or when the coolant  16  warms up to a predetermined temperature, and the actuator  46  actuates the membrane  36  pushing the membrane  36  to deflect to a second position, shown in dashed as SP, and having a generally concave shape with respect to the interior of the bladder  14 . Alternatively, when a voltage is applied to the membrane  36  or when a mechanical force is applied to the membrane after the engine is started, the membrane deflects to the second position SP. 
         [0020]    The change in the second volume V 2  is about 4% to 8% of the total coolant volume of the vehicle cooling system, however other values are possible. In position SP, the second volume V 2  of air is increased as the air from the top volume of the tank body  12  above the coolant surface CEL are pushed to the second volume V 2 . The CEL rises in the tank body  12 , decreasing the upper volume  20  of air. Typically, the amount of coolant  16  of first volume V 1  in the expansion tank  10  remains about the same, assuming the input from coolant input  30  into the tank body  12  and the output from coolant output  26  out of the tank body  12  are about the same. 
         [0021]    When the membrane  36  is in position SP, the air from the upper volume  20  is displaced through a communicating line  38  where it is fluidly communicated to the second volume V 2  of air. The communicating line  38  allows the CEL to rise in the “Up” direction indicated in  FIG. 1  so that the CEL can be at or higher than the coolant fill level of the engine. When the membrane  36  returns to position FP, the air in the bladder  14  displaces through the communicating line  38  to the upper volume  20 . 
         [0022]    Should coolant  16  be fluidly communicated into the communicating line  38 , the communicating line  38  may have an upward elevation portion  40  that can allow an additional increase of the CEL and also to prevent coolant flow communication with the second volume V 2 . The upward elevation portion  40  may rise in elevation higher than the MCE. However, should coolant  16  be communicated to the bladder  14 , a coolant drain  42  is provided to permit the discharge of coolant from the bladder. It is possible that coolant drain  42  may be in fluid communication with communication line  38  for any residual coolant in the second volume V 2  to be sucked back to the first volume V 1 , for example if the communication line  38  is connected at the bottom surface  28 . A pressure cap  44  is also disposed in fluid communication with the bladder  14  to control the pressure in the expansion tank  10 . 
         [0023]    Turning now to  FIG. 2 , a second embodiment of expansion tank is indicated generally at  110  and is generally similar in operation to the expansion tank  10 . The expansion tank  110  has a tank body  112  with a first volume V 1  of coolant  16 , and a bladder  114  disposed in the tank body  112  having a second volume V 2 . The tank body  112  is generally truncated prism-shaped, however other shapes are possible. The first volume V 1  is configured to receive the liquid coolant  16  of the cooling system  18 . The cooling system  18  is associated with the engine (not shown) having a coolant fill level (CFL) and maximum coolant elevation (MCE). During operation of the cooling system  18 , the CEL needs to be at least as high in elevation as the CFL of the engine. 
         [0024]    The second volume V 2  in the bladder  114  is configured to be filled with air. An upper volume  120  of the tank body  12  located above the CEL is also filled with air. It is possible that the second volume V 2  and the upper volume  120  can be filled with a fluid other than air and coolant vapors. 
         [0025]    A coolant cap  122  is disposed at a top surface  124  on the tank body  112 . A coolant output  126  is disposed at a bottom surface  128  on the tank body  112  to fluidly communicate coolant  16  to the cooling system  18 . One or more coolant inputs  130  fluidly communicate the coolant  16  from the cooling system  18  to the tank body  112 . 
         [0026]    In the expansion tank  110 , the bladder  114  is located at a lower half portion  132  of the tank body  112  such that air is located beneath the CEL. At least a portion of the second volume V 2  is at a lower elevation than the CEL. 
         [0027]    In the expansion tank  110 , the bladder  114  has at least one rigid wall  134  and at least one flexible membrane  136  that is operable to change the volume V 2  of air. In the expansion tank  110 , the bladder  114  is located at the bottom surface  128  of the tank body  112 , the flexible membrane  136  has a generally horizontal orientation, and the rigid wall  134  has a generally vertical orientation, however other configurations of bladder  114  are possible. 
         [0028]    Similar to the expansion tank  10 , the membrane  136  has a first position, shown in dashed as FP, and having a generally convex shape with respect to the interior of the bladder  114 . In position FP, the second volume V 2  is decreased, the upper volume  20  is increased, and the CEL lowers. 
         [0029]    When the engine starts up, the actuator  46  actuates the membrane  136  to deflect to a second position, shown in dashed as SP, and having a generally concave shape with respect to the interior of the bladder  114 . In position SP, the second volume V 2  is increased, the upper volume  120  is decreased, and the CEL rises. 
         [0030]    A communicating line  138  communicates air between the upper volume  120  to the second volume V 2 . An upward elevation portion  40  that acts as a stop to prevent further coolant  16  communication along the communicating line  138 . A coolant drain  142  and a pressure cap  144  are also in fluid communication with the bladder  114 . 
         [0031]    With the expansion tank  10 ,  110  having the moveable membrane  36 ,  136 , the CEL elevation can be changed. When the CEL elevation can be raised higher, then the expansion tank  10 ,  110  can be positioned lower with respect to the other cooling system components  18 .