Abstract:
A plugged filter detection system includes a valve housed within a cavity defining an initial inlet for receiving fluid at an inlet pressure before fluid enters a filter, a final inlet for receiving fluid at an outlet pressure after the fluid exits the filter, and a switch port for directing fluid to a switch to activate the switch. The inlet pressure biases the valve in a first direction and the outlet pressure biases the valve in a second direction substantially opposing the first direction. The valve is movable from a first position to a second position to unblock the switch port, thereby allowing the switch to be activated when inlet pressure is greater than outlet pressure. A spring preferably biases the valve in the second direction, such that inlet pressure must be greater than outlet pressure by at least the spring constant to allow switch activation.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to filters for use within automotive vehicles, and specifically to a system for detecting when a filter is plugged.  
       BACKGROUND OF THE INVENTION  
       [0002]     Motor vehicles use a wide variety of filters. As one example, oil typically flows through an oil filter to remove contamination from an oil stream. Filters are generally designed to be replaceable. However, without an accurate way to measure when a filter should be replaced, consumers may wait too long prior to replacement, or alternatively replace filters too often.  
       SUMMARY OF THE INVENTION  
       [0003]     A plugged filter detection system includes a valve housed within a cavity. The cavity defines an initial inlet for receiving fluid at an inlet pressure before fluid enters a filter, and a final inlet for receiving fluid at an outlet pressure after the fluid exits the filter. The cavity also defines a switch port for directing fluid to a switch to activate the switch. The inlet pressure biases the valve in a first direction and the outlet pressure biases the valve in a second direction substantially opposing the first direction. The valve is movable from a first position, wherein the switch port is blocked, to a second position, wherein the switch port is unblocked, thereby allowing the switch to be activated when inlet pressure is greater than outlet pressure. In one aspect of the invention, the system further includes a spring having a spring constant. The spring biases the valve in the second direction, such that the inlet pressure must be greater than the outlet pressure by at least the spring constant for the valve to move from the first position to the second position. The filter is preferably in parallel with the system.  
         [0004]     The system may include a stop to prevent movement of the valve beyond the second position. The cavity may further define an exhaust port, with the exhaust port releasing at least a portion of the fluid when the valve is in the second position. Fluid entering the cavity through the initial inlet may travel through the switch port to activate the switch when the valve is in the second position. Alternatively, the cavity may further define an activation inlet, with fluid entering the cavity through the activation inlet at a control pressure and traveling through the switch port to activate the switch when the valve is in the second position. In this type of embodiment, the valve preferably blocks the activation inlet when the valve is in the first position.  
         [0005]     The final inlet may be coupled to a vehicle lockup clutch, such that fluid only enters the cavity through the final inlet when the lockup clutch is engaged. A vehicle controller may be operable to disengage the lockup clutch to reduce the outlet pressure, thus causing the valve to move to the second position if the system is working properly. Failure of the valve to move to the second position when the lockup clutch is disengaged may indicate that the valve and/or the switch are not working properly. The system may further include a pump upstream of the initial inlet, with failure of the valve to move to the second position when the lockup clutch is disengaged indicating that the pump is not working properly.  
         [0006]     The valve may create a hysteresis effect within the cavity, such that movement of the valve partially toward the second position causes the valve to complete movement to the second position. As such, the hysteresis effect provides stability within the system. As one example, the valve may include at least two portions of varying diameter, with the varying diameter portions causing the hysteresis effect.  
         [0007]     The above features and advantages, and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic side view of a first embodiment of a plugged filter detection system according to the present invention, showing the valve of the system in a first position indicating an unblocked filter;  
         [0009]      FIG. 2  is a schematic side view of the plugged filter detection system of  FIG. 1  showing the valve in a second position indicating a blocked filter;  
         [0010]      FIG. 3  is a schematic view of fluid entering and exiting a filter;  
         [0011]      FIG. 4  is a schematic side view of a second embodiment of a plugged filter detection system according to the present invention, showing a valve of the system in a first position indicating an unblocked filter; and  
         [0012]      FIG. 5  is a schematic side view of the plugged filter detection system of  FIG. 4  showing the valve in a second position indicating a blocked filter. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     Referring to the drawings, wherein like reference numbers refer to like components,  FIGS. 1 and 2  present a side view of a first embodiment of a plugged filter detection system  10  according to the present invention. A valve  12  housed within a cavity  14  is movable from a first position, shown in  FIG. 1 , to a second position, shown in  FIG. 2 . The cavity  14  defines an initial inlet  16  and a final inlet  18 . As shown schematically in  FIG. 3 , fluid  15  enters the cavity  14  of  FIG. 1  through the initial inlet  16  at an inlet pressure just before entering a filter  17 , and through the final inlet  18  at an outlet pressure upon exiting the filter  17 . Thus, the system  10  is in parallel with the filter  17 . For example, oil within a motor vehicle could enter the inlets  16 ,  18  upon entry to and exit from an oil filter. It should be noted that fluid may enter the cavity  14  other than as described herein. For example, typically the system  10  will be used within a motor vehicle and be somewhat saturated with oil. Thus it is important to note that the system works based on fluid entering the initial inlet  16  at an inlet pressure, and through the final inlet  18  at an outlet pressure.  
         [0014]     Turning back to  FIGS. 1 and 2 , fluid entering the initial inlet  16  impinges upon the valve  12  at the inlet pressure, tending to push the valve  12  to the right with respect to  FIGS. 1 and 2 . Similarly, fluid entering the final inlet  18  impinges upon the valve  12  at the outlet pressure, tending to push the valve  12  left with respect to  FIGS. 1 and 2 . If the fluid lost no pressure within the filter, such that inlet pressure was equal to outlet pressure, the forces upon the valve  12  at inlet  16  would be equal to the forces upon the valve  12  at inlet  18 , and the valve  12  would remain in the first position. If the fluid loses pressure within the filter, the pressure on the valve  12  at inlet  16  (i.e., the inlet pressure) would be greater than the pressure on the valve  12  at inlet  18  (i.e., the outlet pressure), and the inlet pressure would push the valve toward the right with respect to  FIGS. 1 and 2  to the second position, wherein the valve  12  abuts a stop  22 . A pin  23  may keep the stop  22  in position. Movement of the valve  12  to the second position opens a switch port  24 , allowing fluid to flow from the cavity  14  to a switch  26 , thus activating the switch  26  to indicate an undesirable fluid pressure drop due to a plugged filter.  
         [0015]     In practice, fluid will experience at least a partial drop in pressure upon travel through a filter, even when the filter is not plugged. Also, a small amount of filter clogging may not necessitate filter cleaning or replacement. Thus, a spring  20  biases the valve  12  toward the left with respect to  FIGS. 1 and 2 , with the spring  20  having a spring constant equal to the allowable pressure drop. For instance, the spring  20  may have a spring constant of 25 psi, indicating that fluid may lose 25 psi of pressure within the filter without opening the switch port  24  to trigger the switch  26 . The cavity  14  also preferably defines an exhaust port  28 . When the valve  12  is in the second position, the exhaust port  28  opens to allow a portion of the fluid to exit therethrough. Dissipation of fluid through the exhaust port  28  increases fatigue life of the switch  26  by reducing the pressure fluid traveling through the switch port  24  exerts on the switch  26 . The relative size of the initial and final inlets  16 ,  18  determines the fluid pressure exerted on the switch  24 . For example, if the initial and final inlets  16 ,  18  are similarly sized, with an inlet pressure of 230 psi and an outlet pressure of 10 psi, the initial and final inlets  16 ,  18  will share a pressure drop of 110 psi ([230 psi−10 psi]/2), and the pressure at the switch  24  will be 120 psi ([230 psi+10 psi]/2).  
         [0016]      FIGS. 4 and 5  present side views of a second embodiment of a plugged filter detection device  110 . A valve  112  housed within a cavity  114  is movable from a first position, shown in  FIG. 4 , to a second position, shown in  FIG. 5 . The valve  112  preferably includes a larger diameter portion  112   a  and a smaller diameter portion  112   b . The cavity  114  defines an initial inlet  116 , a final inlet  118 , an exhaust port  128 , a switch port  124 , and an activation inlet  130 . Fluid enters the cavity  114  through the initial inlet  116  at an inlet pressure just before entering a filter (i.e.,  17  of  FIG. 3 ), and enters through the final inlet  118  at an outlet pressure upon exiting the filter. Fluid entering the initial inlet  116  at the inlet pressure impinges upon the valve  112 , tending to push the valve  112  downward with respect to  FIGS. 3 and 4 , while fluid entering the final inlet  118  at the outlet pressure impinges upon the valve  112 , tending to push the valve upward with respect to  FIGS. 3 and 4 . A spring  120  having a spring constant equivalent to the desired allowable pressure drop biases the valve  112  upward.  
         [0017]     If the fluid pressure of the fluid entering the initial inlet  116  is greater than the fluid pressure of the fluid entering the final inlet  118  by enough to overcome the force of the spring  120 , the valve  112  will move downward to the second position, thereby uncovering the activation inlet  130  and allowing fluid to enter the cavity  114  therethrough. Fluid flows through the activation inlet  130  at a steady predetermined control pressure, for example 100 psi. Fluid from the activation inlet  130  then travels around the smaller diameter portion  112   b  of the valve  112  through the switch port  124  to activate a switch  126  indicating an undesirable drop in fluid pressure due to a plugged filter. The larger diameter portion  112   a  of the valve  112  blocks fluid that has entered the cavity  114  through the inlet port  116  from reaching the switch  126  in this embodiment, thereby allowing even greater control of the force at which fluid hits the switch  126 . Additionally, using varying diameter portions  112   a ,  112   b  for the valve  112  also causes a hysteresis effect within the cavity  114 , such that once the valve  112  proceeds downward with respect to  FIGS. 4 and 5  beyond a half-way position, the valve hysteresis effect will cause the valve  112  to snap downward the rest of the way to the second position. The hysteresis effect will further cause the valve  112  to remain in the second position until the pressure drop across the filter is reduced enough to adequately overcome the pressure produced by the differential area of the two portions  112   a ,  112   b . It can thus be seen that the hysteresis effect produced by the use of varying diameter portions  112   a ,  112   b  provides stability within the system  110  by preventing the valve  112  from cycling between the first and second positions.  
         [0018]     In addition to detecting a plugged filter, the second embodiment  110  of the present invention provides novel diagnostic capabilities. A vehicle includes a logic valve which selectively activates a lockup clutch  132 . When the lockup clutch  132  is engaged, a vehicle torque converter clutch is pressurized. Conversely, when the lockup clutch  132  is disengaged, the torque converter clutch is exhausted. Preferably, the final inlet  118  is coupled to the lockup clutch  132 , as shown schematically in  FIGS. 4 and 5 , such that fluid pressurizes the cavity  114  through the final inlet  118  only when the lockup clutch  132  is engaged. When a vehicle engine is started, typically the lockup clutch  132  is disengaged. Thus, fluid enters the cavity  114  through the initial inlet  116 , but not through the final inlet  118 , causing the valve  112  to move to the second position, thereby activating the switch  126 . If the switch  126  does not activate upon engine start, that indicates to a vehicle controller  134  that either the valve  112  is stuck in the first position, or the switch  126  is broken. When the controller  134  activates the logic valve to engage the lockup clutch  132 , fluid should pressurize the cavity  114  through the final inlet  118 , thereby moving the valve  112  upward once again and deactivating the switch  126  as the activation inlet  130  becomes blocked. If the switch  126  does not turn off, that indicates to the vehicle controller  134  either that the valve  112  is stuck downward, the filter is plugged, or there is some problem with the connection between the final inlet  118  and the lockup clutch  132 . Failure of the valve  112  to move from the first position to the second position when the lockup clutch  132  is disengaged may also indicate a problem with a vehicle pump  136 . Specifically, if the pump  136  has not primed, or has lost its prime, fluid within the system  110  will not be pressurized, and minimal fluid will enter the cavity  114 . Thus if the lockup clutch  132  is disengaged to prevent fluid from entering the cavity  114  through the final inlet  118 , but the pump  136  is not working properly such that fluid does not enter the cavity  114  through the initial inlet  118 , the valve  112  will remain in the first position. It can thus be seen that the present invention provides diagnostic capabilities beyond detection of a plugged filter.  
         [0019]     While the best modes for carrying out the invention have been described in detail, it is to be understood that the terminology used is intended to be in the nature of words and description rather than of limitation. Those familiar with the art to which this invention relates will recognize that many modifications of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced in a substantially equivalent way other than as specifically described herein.