Abstract:
An easily adjustable pressure relief valve for adjusting maximum fluid pressure levels in automatic transmissions at events. Engines used in racing and exhibitions require automatic transmissions with increased fluid pressure to prevent slipping during shifts. The pressure relief valve replaces a main mod line solenoid accumulator and includes an easily replaceable spring allowing adjustment of maximum fluid pressure at each event. The relief valve spring is selectable to adjust maximum fluid pressure for each event.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to automatic transmissions and in particular to controlling peak pressures in automatic transmissions modified to operate at high pressures for use with increased torque. 
     There is a growing interest in high performance applications of vehicles with diesel engines. Such engines are being modified to produce between 1,000 and 4,000 foot pounds of torque or there about for tractor pull and drag racing events. Such high torque levels generally result in automatic transmission clutches slipping. To reduce such slipping, the transmissions are modified to increase the transmission fluid pressure in the transmissions. Normal fluid pressure is typically 85 PSI, and under throttle up to 240 PSI, briefly, but the pressures required to prevent slipping in the under up to 4,000 foot pounds of torque may be as high as 325 to 450 PSI. 
     Fluid pressure in the transmission may be raised by using a stiffer spring in the main pressure regulator. For example, during overhaul the main pressure regulator valve spring may be replaced to raise maximum fluid pressure from 85 PSI to 250 to 285 PSI. However, the main pressure regulator established a minimum pressure, and, for example, during a shift when a clutch might slip, the operating pressure is increased by the main mod line solenoid which momentarily raises the operating pressure by as much as 180 PSI by adding fluid pressure to the main pressure regulator spring pressure. 
     Each of the tractor pull and drag racing events require different engine settings, for example, some events benefit from very high torque output and other only require a lower torque output to be competitive. Running at high torque in every event requires greater engine maintenance and costs, and as a result, teams often run at lower torque levels. The lower torque levels allow lower pressure in the transmission which would also reduce transmission failures. The ability to run at lower torque levels may not be understood until the conditions at the events determined at the time of the event. 
     Unfortunately, known methods require replacing the main pressure regulator spring to adjust transmission pressure, and replacing the main pressure regulator spring requires removing the transmission which is often not feasible at an event. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing an easily adjustable pressure relief valve for adjusting maximum fluid pressure levels in automatic transmissions at events. Engines used in racing and exhibitions require automatic transmissions with increased fluid pressure to prevent slipping during shifts. The pressure relief valve replaces a main mod line solenoid accumulator and includes an easily replaceable spring allowing adjustment of maximum fluid pressure at each event. The relief valve spring is selectable to adjust maximum fluid pressure for each event. 
     In accordance with one aspect of the invention, there is provided a method for modifying an automatic transmission to allow easily adjusting maximum pressure. The method includes removing the pan from an automatic transmission, removing the accumulator plate from the automatic transmission, removing a main mod line solenoid accumulator from an accumulator seat in a shift valve body of the automatic transmission, placing a relief valve body in the accumulator seat, placing a relief valve ball in the relief valve body, placing a relief valve spring in the relief valve body resting against the relief valve ball, replacing the accumulator plate, and replacing the pan. The maximum pressure may then be easily adjusted without removing the transmission from the vehicle. 
     In accordance with another aspect of the invention, there is provided a method for adjusting fluid pressure in an automatic transmission. The method includes measuring the fluid pressure in the automatic transmission, selecting a new relief valve spring to adjust the fluid pressure, removing the pan from an automatic transmission, removing the accumulator plate from the automatic transmission, removing a relief valve spring in the relief valve body resting against the relief valve ball, replacing the relief valve spring in the relief valve body resting against the relief valve ball, replacing the accumulator plate, and replacing the pan. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  shows a schematic of a prior art automatic transmission. 
         FIG. 2  shows the prior art automatic transmission with a pan and accumulator plate removed. 
         FIG. 3  shows a main solenoid circuit of the prior art automatic transmission. 
         FIG. 4  shows modified main solenoid circuit according to the present invention. 
         FIG. 5A  is a side view of a relief valve body according to the present invention. 
         FIG. 5B  is an end view of the relief valve body according to the present invention. 
         FIG. 6  is a cross-sectional view of the relief valve body according to the present invention taken along line  6 - 6  of  FIG. 5A . 
         FIG. 7  is a relief valve ball according to the present invention. 
         FIG. 8  is a relief valve spring according to the present invention. 
         FIG. 9  is a method according to the present invention for modifying an automatic transmission to allow easy adjustment of maximum fluid pressure. 
         FIG. 10  is a method according to the present invention for adjusting maximum fluid pressure in an automatic transmission. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     A schematic  10  of a prior art automatic transmission  50  (see  FIG. 2 ) is shown in  FIG. 1 . The automatic transmission  50  includes a sump  12  holding transmission fluid, a pump  14  circulating the transmission fluid through the automatic transmission  10 , a main pressure regulator  16  for regulating fluid pressure in the automatic transmission  10 , a main mod line solenoid  18  for using a pressure control signal  19  to boost fluid pressure from the main pressure regulator  16  to the clutches  22  and other components during shifts, and a main mod line solenoid accumulator  20  on an outlet of the main mod line solenoid  18  to dampen high frequency fluctuations in the pressure control signal  19 . Transmissions used in tractor pull events and racing often require higher fluid pressure to prevent slipping. Such desired higher pressure is obtained by adding a stiffer main pressure regulator valve spring to raise, for example, a base fluid pressure to as much as 250 PSI, however such base fluid pressures can be boosted to as high as 370 PSI by a Transmission Control Unit (TCU) controlling the main mod solenoid  18  by raising fluid pressure from the main pressure regulator  16  by, for example, 120 PSI. Various combinations of main pressure regulator valve springs  16   a  (see  FIG. 4 ) and relief valve springs  28  (see  FIG. 8 ) can be combined according to the present invention to establish a desired base fluid and a desired boosted pressure. Achieving a higher than necessary pressure can unnecessarily damage the transmission. Unfortunately, changing the main pressure regulator valve spring to adjust the maximum pressure requires removing the transmission  50  from the vehicle, and is not feasible at events to adjust the pressure for each event. 
     A prior art automatic transmission  50  with a pan  52  and accumulator plate  54  removed is shown in  FIG. 2 . Removing the pan  52  and accumulator plate  54  provides access to a shift valve body  56  in the transmission housing  56 . 
     A main solenoid circuit  11   a  of the prior art automatic transmission  50  is shown in  FIG. 3 . The main solenoid circuit  11   a  includes the sump  12  holding transmission fluid  13 , the pump  14  circulating the transmission fluid  15  through the automatic transmission  10 , the main pressure regulator  16  controlling fluid  17  pressure provided to clutches  22  of the automatic transmission, and the main mod line solenoid  18  providing the pressure control signal  19  to the main pressure regulator  16 . The accumulator  20  dampens high frequency fluctuations in the pressure control signal  19 . 
     A modified main solenoid circuit  11   b  according to the present invention is shown in  FIG. 4 . The modified main solenoid circuit  11   b  includes the main pressure regulator  16  having a replacement spring  16   a  providing a higher pressure fluid flow  17   a  to the clutches  22  of the automatic transmission  50 . The accumulator  20  is replaced by a relief valve  24 . The relief valve  24  is configured to reside in the cavity provided for the accumulator  20  and is adjustable to control the maximum fluid pressure to the components  22 . The relief valve  24  reduces the pressure control signal  19  to a reduced pressure control signal  19   a  to reduce the higher pressure fluid flow  17   a  to avoid damaging transmission parts. Replacing the replacement spring  16   a  to adjust the higher pressure fluid flow  17   a  requires removing the transmission  50  from the vehicle. A relief valve spring  28  (see  FIG. 8 ) in the relief valve  24  may be replaced to adjust the higher pressure fluid flow  17   a  without removing the transmission  50  from the vehicle. 
     A side view of a relief valve body  24  is shown in  FIG. 5A , an end view of the relief valve body  24  is shown in  FIG. 5B . and a cross-sectional view of the relief valve body  24 , taken along line  6 - 6  of  FIG. 5A , is shown in  FIG. 6 . A relief valve ball  26  is shown in  FIG. 7  and a relief valve spring  28  is shown in  FIG. 8 . The spring  28  pushed the ball  26  against a seat  25  in the relief valve body  24 . The spring  28  is selected to hold the ball  26  against the seat  25  until the pressure of the reduced pressure control signal  19   a  exceeds a safe upper limit, and then the ball  26  is forced off of the seat  25  to release fluid into the sump  12  to limit the pressure of the higher pressure fluid flow  17   a  to the clutches  22 . The reduced pressure control signal  19   a  is preferably less than 115 PSI. 
     A method according to the present invention for modifying an automatic transmission to limit the reduced pressure control signal  19   a  is shown in  FIG. 9 . The method includes removing the pan from an automatic transmission at step  100 , removing the accumulator plate from the automatic transmission at step  102 , removing a main mod line solenoid accumulator from an accumulator seat in a shift valve body of the automatic transmission at step  104 , placing a relief valve body in the accumulator seat at step  106 , placing a relief valve ball in the relief valve body at step  108 , placing a relief valve spring in the relief valve body resting against the relief valve ball at step  110 , replacing the accumulator plate at step  112 , and replacing the pan at step  114 . 
     A method according to the present invention for adjusting fluid pressure in an automatic transmission is shown in  FIG. 10 . The method includes determining a need for higher or lower fluid pressure in an automatic transmission at step  120 , selecting a new relief valve spring to adjust the fluid pressure at step  122 , removing the pan from an automatic transmission at step  124 , removing the accumulator plate from the automatic transmission at step  126 , removing a relief valve spring in the relief valve body resting against the relief valve ball at step  128 , replacing the relief valve spring in the relief valve body resting against the relief valve ball at step  130 , replacing the accumulator plate at step  132 , and replacing the pan at step  134 . 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.