Abstract:
The present invention provides a method and apparatus for a self cleaning logic valve assembly. The logic valve assembly is adapted to cycle and thereby clean itself in response to one or more predefined parameters which are programmed into a programmable controller. The logic valve assembly is additionally configured to cycle according to one or more of several different methods which have been shown to efficiently clean the valve assembly. The cleaning process takes place during a predetermined time period selected to avoid causing an unwanted gear speed ratio change of the vehicle transmission. In this manner, the logic valve assembly may be automatically cleaned while the vehicle is being driven and without interfering with vehicle operation such that the valve cleaning is imperceptible to the operator.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a self cleaning logic valve assembly for a vehicle transmission. 
       BACKGROUND OF THE INVENTION 
       [0002]    Since debris can build up in a valve assembly over time and thereby increase valve friction, it is desirable to provide a self cleaning valve assembly. Logic valves such as those used in the hydraulic control systems of automatic transmissions are particularly prone to debris accumulation because they may remain in a given position for prolonged periods of time. 
         [0003]    The industry standard for valve bore clearances on transmission control systems is 0.0008″ to 0.0023″ diametrical clearance. This allows for 0.0005″ total tolerance on the valve diameter and 0.001″ total tolerance on the valve bore. These tolerances are well established and it is difficult to reduce the tolerance further without much more expensive part processing. It has been observed that if the filtration system does not filter out debris greater than 0.0008″, there is the potential for debris to cause valve sticking. Typically automotive filters trap debris at sizes above 0.0024″. While higher filtration levels can provide better protection, such filters plug too quickly to be practical. 
         [0004]    Valves are particularly sensitive to debris that is about the same size as the valve clearance. Single particles can be wedged between valve and valve body, solidly sticking the valve. Another situation can occur where particles smaller than the diametral clearance can accumulate between the valve and the valve body and gradually increase friction to the point that valve stroke times are delayed or the valve momentarily sticks. Large buildups can cause friction to overcome the return spring force causing the valve to stick in a stroked position. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a method and apparatus for a self cleaning logic valve assembly. The logic valve assembly is adapted to cycle and thereby clean itself in response to one or more predefined parameters which may be programmed into a programmable controller. The logic valve assembly is additionally configured to cycle according to one or more of several different methods which have been shown to efficiently clean the valve assembly. The cleaning process takes place during a predetermined time period selected to avoid causing an unwanted gear speed ratio change of the vehicle transmission. In this manner, the logic valve assembly may be automatically cleaned while the vehicle is being driven and without interfering with vehicle operation such that the valve cleaning is imperceptible to the operator. 
         [0006]    The logic valve assembly may be completely de-stroked and stroked multiple times to clear any debris. Alternatively, the logic valve assembly may be shaken by a high frequency dither, partially de-stroked several times, partially stroked several times, etc. 
         [0007]    The frequency and duration of logic valve assembly cleaning may be based on a vehicle mileage parameter. Alternatively, the frequency and duration of logic valve assembly cleaning may be based any number of other parameters such as time in range, shift density, the time required to stroke the valve, etc. 
         [0008]    It has been observed that cycling the logic valve assembly in the manner described herein efficiently clears valve debris, however, it should be appreciated that any method wherein the logic valve assembly is cycled may be implemented for this purpose. 
         [0009]    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 
         [0010]      FIG. 1  shows a schematic illustration of an exemplary hydraulic control system; 
           [0011]      FIG. 2  shows a schematic cross-sectional view of a self cleaning valve assembly having a valve disposed within a bore of a valve body according to the present invention; 
           [0012]      FIG. 2   a  shows a schematic cross-sectional view of a single large particle disposed between the valve and valve body of  FIG. 1 ; 
           [0013]      FIG. 2   b  shows a schematic cross-sectional view of a plurality of smaller particles disposed between the valve and valve body of  FIG. 1 ; 
           [0014]      FIG. 3  is a graph depicting a method of the present invention wherein the valve is completely de-stroked and stroked multiple times; 
           [0015]      FIG. 4  is a graph depicting a method of the present invention wherein the self cleaning valve assembly of  FIG. 1  is shaken by a high frequency dither; 
           [0016]      FIG. 5  is a graph depicting a method of the present invention wherein the valve is partially de-stroked several times; 
           [0017]      FIG. 6  is a graph depicting a method of the present invention wherein the valve is partially stroked several times; 
           [0018]      FIG. 7  is a graph depicting a method of the present invention wherein the cleaning frequency of the self cleaning valve assembly of  FIG. 1  is based on a vehicle mileage parameter; 
           [0019]      FIG. 8  is a graph depicting a method of the present invention wherein the cleaning frequency of the self cleaning valve assembly of  FIG. 1  is based on a time in range parameter; 
           [0020]      FIG. 9  is a graph depicting a method of the present invention wherein the cleaning frequency of the self cleaning valve assembly of  FIG. 1  is based on a shift density parameter; and 
           [0021]      FIG. 10  is a graph depicting a method of the present invention wherein the cleaning frequency of the self cleaning valve assembly of  FIG. 1  is based on a parameter reflecting the time required to stroke the valve. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Referring to the drawings wherein like reference numbers refer to like components,  FIG. 1  shows a schematic illustration of a hydraulic control system  40  for a vehicle transmission  42 . It should be appreciated that the hydraulic control system  40  is shown for exemplary purposes, and that the present invention is applicable to alternate hydraulic control system configurations. 
         [0023]    The hydraulic control system  40  includes a plurality of logic valves  44 ,  46  and  48 . The logic valves  44 ,  46  and  48  are configured to control the transfer of hydraulic fluid (not shown) to one or more of a plurality of clutches C 1 , C 2 , C 3 , C 4  and C 5 . By controlling the transfer of hydraulic fluid to the clutches C 1 , C 2 , C 3 , C 4  and C 5 , the status of the clutches (i.e., either “engaged” or “released”) is similarly controllable. It should be appreciated by those skilled in the art that by controlling the status of the clutches C 1 , C 2 , C 3 , C 4  and C 5 , the gear speed ratio of the vehicle transmission  42  is also controlled. As an example, when the vehicle transmission  42  is in second gear, clutches C 1  and C 4  are engaged; and when the vehicle transmission  42  is in third gear, clutches C 1  and C 3  are engaged. Therefore, a gear speed ratio change from second gear to third gear can be effected by blocking the transfer of hydraulic fluid to clutch C 4  and transferring hydraulic fluid to clutch C 3 . 
         [0024]    In some circumstances, the logic valves  44 ,  46  and  48  can be actuated or cycled without changing the status of the clutches C 1 , C 2 , C 3 , C 4  and C 5 . Referring to the exemplary hydraulic control system  40 , when the vehicle transmission  42  is in second gear the logic valve  46  is actuatable without changing the status of the clutches C 1 , C 2 , C 3 , C 4  and C 5 . In other words, when the vehicle transmission  42  is in second gear, the clutches C 2 , C 3 , and C 5  remain “released” regardless of valve  46  position; and the clutches C 1  and C 4  remain “engaged” regardless of valve  46  position. Therefore, a vehicle incorporating the hydraulic control system  40  which is being driven in second gear can actuate and thereby clean the logic valve  46  while the vehicle is moving and without interfering with vehicle operation such that the valve cleaning is imperceptible to the operator. 
         [0025]    When the vehicle transmission  42  is in third gear, the logic valve  44  is actuatable without changing the status of the clutches C 1 , C 2 , C 3 , C 4  and C 5 ; and when the vehicle transmission  42  is in fourth gear, the logic valve  48  is actuatable without changing the status of the clutches C 1 , C 2 , C 3 , C 4  and C 5 . While the present invention has been described as applied to the exemplary hydraulic control system  40 , alternate hydraulic control system configuration generally include at least one speed ratio wherein each of the control system logic valves can be actuated without changing the status of the transmission clutches. Accordingly, the logic valves  44 ,  46  and  48  can all be cycled and thereby cleaned at a predetermined time while the vehicle is being driven and without interfering with vehicle operation. 
         [0026]    The hydraulic control system  40  also includes a manual selector valve  50  which is manually positioned by the operator to select a gear speed range (i.e., park, reverse, neutral, drive, etc.); and a torque converter valve  52  configured to control the actuation of a torque converter  54 . Torque converter valve  52  actuation is preferably performed with a torque converter solenoid  56 . A conventional accumulator  58  and exhaust valve  60  are preferably provided to store and release energy in a controllable manner. 
         [0027]    The logic valves  44 ,  46 ,  48 , and the manual selector valve  50 , respectively include a pressure switch  62 ,  64 ,  66 , and  68  configured to measure valve position. The logic valves  44 ,  46  and  48  are each actuated by a shift solenoid  70 ,  72  and  74 , respectively. The hydraulic control system  40  includes a high pressure hydraulic fluid source  76 , and steps down this high pressure level via a plurality of regulator valves  78  configured to maintain a predetermined pressure level. An exhaust passage  80  relieves excess pressure in the spring pocket of the logic valve  44 . An overdrive knockdown device  82  is configured to reduce the hydraulic fluid pressure level when the vehicle transmission  42  is operating in overdrive. 
         [0028]    Referring to  FIG. 2 , a self cleaning logic valve assembly  8  which may represent any of the logic valves  44 ,  46  or  48  (shown in  FIG. 1 ) is shown in more detail. The self cleaning logic valve assembly  8  has a valve  10  disposed within a bore  12  of a valve body  14 . The valve body  14  further defines one or more pressure ports  16  and one or more outlet ports  18 . A return spring  20  engages the valve  10  within the bore  12 . As pressure is introduced into the pressure port  16  the valve  10  is displaced thereby compressing the return spring  20  to open the outlet ports  18 . The logic valve assembly  8  is preferably electronically controlled by a programmable controller  22  adapted to regulate fluid flow into the pressure port  16  and thereby actuate the valve  10 . The programmable controller  22  is further adapted to generate a triggering signal or profile that controls the frequency and duration of valve assembly cleaning. 
         [0029]    As best seen in  FIG. 2   a , a single large particle  24  may become wedged between the valve  10  and the body  14 . Alternatively, as shown in  FIG. 2   b , a plurality of smaller particles  26  may become trapped between the valve  10  and the body  14 . A build-up of debris composed of particles  24  and/or  26  increases valve friction thereby reducing the efficiency of logic valve assembly  8 . The self cleaning logic valve assembly  8  is therefore adapted to automatically clear such debris to maintain optimal valve performance as described in detail hereinafter. 
         [0030]    In a preferred embodiment, the self cleaning logic valve assembly  8  is implemented in a transmission system, however, it should be appreciated that the self cleaning valve may be used with any number of other systems as well.  FIGS. 3-6  which are described in detail hereinafter show several preferred methods for cycling and thereby cleaning a valve assembly, however, it should be appreciated that any method wherein the valve is cycled may be implemented for this purpose. 
         [0031]      FIG. 3  shows a method of the present invention wherein the valve  10  is completely de-stroked and stroked multiple times to clean the logic valve assembly  8 . More precisely,  FIG. 3  is a graph of valve position versus time as the valve  10  is completely de-stroked from the on position to the off position, and thereafter completely stroked from the off position to the on position. The speed and duration of the method of  FIG. 3  are pre-defined according to the needs of a particular application and may be programmed into the programmable controller  22 . 
         [0032]      FIG. 4  shows a method of the present invention wherein the valve  10  is shaken by a high frequency dither that has a duration long enough to physically move the logic valve assembly  8  a slight amount. More precisely,  FIG. 4  is a graph of valve position versus time as the valve  10  is rapidly cycled back and forth between the on position and an intermediate valve position. The frequency of the signal is preferably based on the natural frequency of the valve  10 . 
         [0033]      FIG. 5  shows a method of the present invention wherein the valve  10  is partially de-stroked several times. More precisely,  FIG. 5  is a graph of valve position versus time as the valve  10  is cycled back and forth between the on position and an intermediate valve position. The speed and duration of the method of  FIG. 5  are pre-defined according to the needs of a particular application and may be programmed into the programmable controller  22 . 
         [0034]      FIG. 6  shows a method of the present invention wherein the valve  10  is partially stroked several times. More precisely,  FIG. 6  is a graph of valve position versus time as the valve  10  is cycled back and forth between the off position and an intermediate valve position. The speed and duration of the method of  FIG. 6  are pre-defined according to the needs of a particular application and may be programmed into the programmable controller  22 . 
         [0035]    The frequency and duration of the valve cleaning described herein are preferably programmed into the programmable controller  22  as a function of one or more different parameters or triggers. As an example such parameters may include vehicle mileage, time in range, shift density, throttle, speed changes, oil temperature, oil age, etc.  FIGS. 7-10  show several preferred parameters adapted to control frequency and duration of valve cleaning, however, it should be appreciated that any number of alternate parameters may be implemented for such a purpose. 
         [0036]      FIG. 7  shows a cleaning frequency based on a vehicle mileage parameter. More precisely,  FIG. 7  is a graph of cleaning frequency versus vehicle mileage wherein the logic valve assembly  8  is cleaned less frequently as vehicle mileage increases. The embodiment shown in  FIG. 7  was developed in response to the observation that the majority of sticking valve issues occur in the first 5,000 miles when the transmission  42  (shown in  FIG. 1 ) is going through a clutch break in period (Oil suspended friction element material is present in higher concentrations during the break in period). 
         [0037]      FIG. 8  shows a cleaning frequency based on a time in range parameter. More precisely,  FIG. 8  is a graph of cleaning frequency versus time in range wherein the logic valve assembly  8  is cleaned more frequently if the valve  10  remains in a predefined valve position range for a longer period of time. The embodiment shown in  FIG. 8  was developed in response to the observation that valves are more likely to stick if they remain in a single position for a long period of time. The time in range parameter is particularly well adapted to clear the valve assembly  8  of the buildup of a plurality of fine particles such as the particles  26  shown in  FIG. 2   b.    
         [0038]      FIG. 9  shows a cleaning frequency based on a shift density parameter. More precisely,  FIG. 9  is a graph of cleaning frequency versus shifts per mile wherein the valve assembly  8  is cleaned less frequently as the number of shifts per mile increases. The shift density parameter is particularly well adapted to clear the valve assembly  8  of the buildup of a plurality of fine particle such as the particles  26  shown in  FIG. 2   b.    
         [0039]      FIG. 10  shows a cleaning frequency based on a parameter reflecting the time required to stroke the valve  10 . The time required to stroke the valve  10  may be estimated based on valve position data from pressure switches such as the pressure switches  62 ,  64 ,  66  (shown in  FIG. 1 ); however, any known methods for measuring valve stroke time may also be implemented. An increase in valve friction due to debris reduces efficiency and may increase valve stroke time. Therefore, if the measured valve stroke time exceeds the optimal valve stroke time by a predetermined amount, an increase in valve cleaning frequency may be triggered. In an alternate embodiment, the time required to de-stroke the valve  10  may be compared with the optimal valve de-stroke time to trigger an increase in valve cleaning frequency. 
         [0040]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.