Patent Abstract:
A tire inflation system includes a hose that connects to a tire via a valve stem. A control valve is in fluid communication with the hose and senses when pressure falls below a predetermined minimum value. When this occurs, the control valve automatically opens to re-supply air to the tire until the predetermined minimum value is achieved. A pressure relieve valve is also in fluid communication with the hose. If, for example, ambient temperatures increase, causing tire pressure to increase, then the pressure relief valve automatically vents excessive pressure to atmosphere. The pressure relief valve is set at a predetermined maximum pressure level that is generally at least 5 psi more than the predetermined minimum value.

Full Description:
TECHNICAL FIELD 
     The subject invention relates to a tire inflation system including a pressure relief valve for each tire that automatically vents excessive pressure to atmosphere. 
     BACKGROUND OF THE INVENTION 
     Tire inflation systems are used on vehicles, such as a tractor-trailer vehicle, to maintain tire inflation pressures at a desired tire pressure setting. The tire inflation system draws pressurized air from on-board air tanks that also supply pressurized air to other vehicle systems, such as brake and suspension systems. The tire inflation system includes a control that automatically supplies air from one of the on-board air tanks to an under-inflated tire when tire pressure falls below the desired tire pressure setting. 
     Tire pressures can change during vehicle operation for many different reasons. The tire could have a slow leak caused by an embedded nail or a small puncture. Tire pressure can also change in response to changes in ambient temperature. Increasing the ambient temperature increases tire pressure and decreasing the ambient temperature decreases tire pressure. 
     For example, assume a tractor-trailer starts out in Florida, where the ambient temperature is 100° F., and drives to Minnesota where the ambient temperature is 0° F. This 100 degree decrease in ambient temperature will cause an approximate 20 psi decrease in tire pressure. In this situation, the tire inflation system will add air to the tires in response to the change in temperature as it would if there were a tire leak caused by a nail. 
     However, if the tractor-trailer starts out in Minnesota where the ambient temperature is 0° F., and drives to Florida, where the ambient temperature is 100° F., the tire inflation system does not typically respond accordingly. The 100 degree increase in ambient temperature will cause an approximate 20 psi increase in tire pressure. Traditionally, tire inflation systems, such as those used on commercial tractor-trailer vehicles, do not have a way of deflating over-inflated tires. Thus, the tire inflation system does not react when the tires are pressurized higher than the desired tire pressure setting and a vehicle operator may think that the tire inflation system is not operating properly. 
     It would be beneficial to provide a tire inflation system with a simple and effective way to control excessive tire pressure in addition to maintaining tire pressure at a desired tire pressure setting. 
     SUMMARY OF THE INVENTION 
     A tire inflation system includes a pressure line that is connected to a tire through a valve stem. The pressure line and the tire are effectively maintained at a common pressure. A control valve is in fluid communication upstream with a fluid supply and is in fluid communication downstream with the pressure line. The control valve senses when tire pressure falls below a desired pressure setting and automatically opens to allow pressurized fluid from the fluid supply to bring pressure in the tire back up to the desired pressure setting. A pressure relief valve is also in fluid communication with the pressure line. The pressure relief valve automatically vents to atmosphere when tire pressure exceeds a maximum pressure setting. This prevents the tire from experiencing excessive pressures in response to changes in ambient temperatures. 
     In one example, the maximum pressure setting is at least 5 psi greater than the desired pressure setting. This prevents the control valve and pressure relief valve from constantly cycling around a single tire pressure setting. This also prevents pressure from venting due to an approximately 5 psi pressure increase normally associated with increase in tire temperature due to over road operations. 
     Preferably, each tire that is coupled to the tire inflation system has a separate pressure line connection. In this configuration, each pressure line connection has a pressure relief valve. In other words, each tire has its own pressure relief valve. All of the pressure relieve valves operate independently from each other. Thus, if only one tire is over-inflated, only the pressure relief valve at that tire is activated. 
     Incorporating a pressure relief valve into a pressure line connection for a tire is a simple and cost effective way to prevent tires from operating at excessive pressures. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic overhead view of a trailer axle assembly with a tire inflation system incorporating the subject invention. 
         FIG. 2  is a perspective view of one side of the trailer axle assembly of  FIG. 1 . 
         FIG. 3  is an exploded view of a wheel-end assembly with the tire inflation system incorporating the subject invention. 
         FIG. 4  is a schematic view of a control system for the tire inflation system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A trailer axle assembly  10  is shown in  FIG. 1 . The trailer axle assembly  10  includes a first non-drive axle  12  and a second non-drive axle  14  that are typically positioned near a rear end portion of a trailer  16 . A front end of the trailer  16  is typically supported on a tractor structure (not shown) as is known in the art. While only two non-drive axles are shown, it should be under stood that additional or fewer non-drive axles could be used to support the trailer  16 . 
     A tire inflation system  18  includes a fluid supply tank  20 , a controller  22  in fluid communication with the fluid supply tank  20  via a first connection  24 , and a second connection  26  that extends to the first  12  and second  14  non-drive axles. While the tire inflation system  18  is shown as being used on a non-drive trailer axle, it should be understood that the tire inflation system  18  could also be used for drive or non-drive axles for a tractor or other similar vehicle. Further, the fluid supply tank  20  is preferably an air tank that is used for the trailer brake and/or suspension system. Optionally, a separate fluid supply tank could be included on the trailer  16 . 
     The first  12  and second  14  non-drive axles each include an axle housing  28  that defines a sealed inner cavity  30 . The second connection  26  includes a first portion  26   a  that is in fluid communication with the sealed inner cavity  30  of the first non-drive axle  12  and a second portion  26   b  that is in fluid communication with the sealed inner cavity  30  of the second non-drive axle  14 . 
     The first non-drive axle  12  defines a first lateral axis of rotation A 1 , and includes a first set of wheels  32  positioned at one end of the axle housing  28  and a second set of wheels  34  laterally spaced from the first set of wheels  32  at an opposite end of the axle housing  28 . The second non-drive axle  14  defines a second lateral axis of rotation A 2 , and includes a first set of wheels  36  positioned at one end of the axle housing  28  and a second set of wheels  38  laterally spaced from the first set of wheels  36  at an opposite end of the axle housing  28 . Each of the first  32 ,  36  and second  34 ,  38  sets of wheels includes either one (1) or two (2) tires  40 . The tire inflation system  18  is in fluid communication with each of the tires  40 . 
     As shown in greater detail in  FIG. 2 , a third connection  42  is in fluid communication with each axle housing  28  and extends outboard of the first sets of wheels  32 ,  36 . The third connection  42  is in fluid communication with the tires  40 . In the example shown in  FIGS. 1 and 2 , the first sets of wheels  32 ,  36  each include a pair of tires  40 , i.e. each first set of wheels  32 ,  36  includes a first tire  40   a  and a second tire  40   b . The third connection  42  includes a first portion  42   a  that is in fluid communication with the first tire  40   a  and a second portion  42   b  that is in fluid communication with the second tire  40   b . While only the first sets of wheels  32 ,  36  are shown in  FIG. 2 , it should be understood that the second sets of wheels  34 ,  38  are configured in a similar manner. 
     Each of the first  24 , second  26 , and third  42  connections is comprised of a pressurized line or hose assembly as is known in the art. The pressurized lines and/or hose assemblies can be rigid members, flexible members, or can be a combination of rigid and flexible members. 
     An example of a wheel end assembly  50  is shown in  FIG. 3 . The wheel ends assembly  50  is similarly configured for each of the first  32 ,  36  and second  34 ,  38  sets of wheels. The wheel end assembly  50  includes a non-rotating spindle  52  that is either attached to or integrally formed with the axle housing  28 . A press plug  54  is inserted into one end of the non-rotating spindle  52 . A stator  56  is inserted into the press plug  54  and is in fluid communication with the sealed inner cavity  30  of the axle housing  28 . The stator  56  is a hollow tube that is fixed to the non-rotating spindle  52  and press plug  54 . Appropriate seal assemblies (not shown) are incorporated into the press plug  54 , stator  56 , and/or hubcap  58  as known. 
     A tee-connection  60  is in fluid communication downstream with the stator  56  via a connecting tube  55 , and is in fluid communication upstream with the third connection  42 . A first arm  62  of the tee-connection  60  is in fluid communication with the first portion  42   a  and a second arm  64  is in fluid communication with the second portion  42   b . The first  42   a  and second  42   b  portions are respectively in fluid communication with the first  40   a  and second  40   b  tires via valve stem assemblies (not shown). 
     A pressure relief valve  66  is in fluid communication with each of the first  42   a  and second  42   b  portions of the third connection  42 . Any type of pressure relief valve  66  known in the art could be used. The pressure relief valve  66  automatically vents pressurized fluid to atmosphere under predetermined conditions. The operation of the pressure relief valve  66  will be discussed in greater detail below. 
     The controller  22  is shown in greater detail in  FIG. 4 . The controller  22  includes a pressure protective valve  70 , a shut-off valve  72 , a filter  74 , a control valve  76 , and a flow-sensing switch  78 . The control valve  76  and flow-sensing switch  78  are preferably enclosed within a control box or housing  80 . The pressure protection valve  70  is located upstream of the control valve  76 , near the fluid supply tank  20 . The pressure protection valve  70  prevents system pressure in the fluid supply tank  20  from falling below a predetermined minimum system pressure. Typically, the pressure protection valve  70  is set at a pressure of around 80 psi while pressure in the fluid supply tank  20  is generally at a pressure of 130 psi. If one of the tires  40  experiences a blow-out or if one of the pressurized lines in the tire inflation system  18  is cut or somehow unsealed, the pressure protection valve  70  will automatically activate to prevent further fluid from being supplied to the damaged component once pressure falls below 80 psi. 
     The shut-off valve  72  allows a vehicle operator to shut off the tire inflation system  18 . This allows the vehicle operator to perform service and maintenance operations. The filter  74  prevents contaminants from entering the control valve  76  and other downstream components. 
     The control valve  76  automatically activates to open fluid communication between the fluid supply tank  20  and the second connection  26  when pressure in any one of the first  42   a  or second  42   b  portions of the third connection  42  falls below a desired minimum pressure. Typically, a desired minimum pressure for each of the tires  40  is around 100 psi. When the first  42   a  and second  42   b  portions are connected to valve stem assemblies of the first  40   a  and second  40   b  tires, respectively, the first  42   a  and second  42   b  portions become part of the first  40   a  and second  40   b  tires. In other words, the first tire  40   a  and the first portion  42   a  are in constant fluid communication and are approximately maintained at a common fluid pressure, and the second tire  40   b  and the second portion  42   b  are in constant fluid communication and are approximately maintained at a common fluid pressure. Further, the first  40   a  and second  40   b  tires are maintained at a common fluid pressure with each other. Thus, if either of the first  42   a  or second  42   b  portions of the third connection  42  is cut or punctured, the respective first  40   a  or second  40   b  tire will deflate. 
     However, fluid pressure in each of the first  40   a  and second  40   b  tires is maintained separately. If the first portion  42   a  of the third connection  42  is punctured, only the first tire  40   a  will deflate. The second portion  42   a  and second tire  40   b  will remain pressurized. 
     All system pressure downstream of the control valve  76  is maintained at a common pressure. Thus, the sealed inner cavities  30 , the second connection  26 , the third connection  42 , and the tires  40  are all at a common pressure. If the desired minimum pressure is set at 100 psi, then all of these components are at 100 psi. The control valve  76  senses when pressure falls below 100 psi. Thus, if any one of the tires  40  has a slow leak or an embedded nail, for example, the control valve  76  will sense the pressure drop and will automatically open to re-supply the under-inflated tire with fluid. Any type of control valve  76  known in the art could be used. 
     When the tire inflation system  18  is active, i.e. when the control valve  76  is open and a tire is being re-supplied with fluid, the flow-sensing switch  78  senses fluid flow and generates a signal that is communicated to the vehicle operator. The signal can be used to activate a warning lamp or display in a vehicle cab to inform the vehicle operator that the tire inflation system  18  is active. If the warning lamp repeatedly comes on or is continuously on, the vehicle operator can determine whether additional tire maintenance is required. 
     If tire pressure exceeds a maximum pressure threshold, the pressure relief valves  66  automatically vent excessive pressure to atmosphere. This prevents tires  40  from operating at excessive tire pressures. Each tire  40  has its own pressure relief valve  66 . Preferably, the pressure relief valves  66  are set to vent at a pressure approximately 5 psi greater than a desired minimum pressure. Thus, if the desired minimum pressure were 100 psi then the pressure relief valves  66  would be set at 105 psi. The difference of 5 psi is required to prevent the tire inflation system  18  and pressure relief valve  66  from “fighting” each other and constantly cycling around a single tire pressure setting. Also, the difference prevents the pressure relief valve  66  from venting air from the tire during the approximately 5 psi increase in tire pressure normally associated with the increase in tire temperature due to over the road operations. 
     Tire pressure could increase for many different reasons. For example, changes in ambient temperature affect tire pressures. In a first example, a trailer fitted with a tire inflation system is located in Minnesota where in the winter a typical ambient temperature could be 0° F. The trailer is then hauled to Florida where the temperature is 100° F. This 100 degree increase in temperature will cause an approximate 20 degrees increase in tire pressure. The pressure relief valve  66  senses when a tire pressure exceeds a maximum threshold pressure and automatically vents excessive pressure to the atmosphere. 
     The reverse situation is also accommodated by the tire inflation system  18 . In this example, a trailer fitted with a tire inflation system is located in Florida where the temperature is 100° F. The trailer is then hauled to Minnesota where the ambient temperature is 0° F. This 100 degree decrease in temperature will cause an approximate 20 degrees decrease in tire pressure. The control valve  76  senses the drop in pressure and automatically re-inflates the tires  40  to the desired level. 
     Thus, the subject tire inflation system  18  automatically addresses both increases and decreases in ambient temperature to maintain tire pressure levels at a desired pressure. It should be understood that the tire inflation system  18  shown in  FIGS. 1-4  is just one example of a tire inflation system, and that tire inflation systems can have other configurations. The subject invention of using the pressure relief valves  66  to automatically vent excessive pressure in response to increases in ambient temperature can be used in any tire inflation system configuration. 
     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Technology Classification (CPC): 5