Abstract:
A latch valve includes a first port containing line pressure, a second port containing control pressure, a third port located between the first and second ports, alternately connecting the first and second ports to a transmission control element, and a fourth port containing control pressure that tends to close the second port and open the first port in opposition to a spring force.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a regulator spool valve controlled by a direct acting solenoid with a multiplex latch valve and located in a machined main control casting of an automatic transmission. 
     2. Description of the Prior Art 
     An automatic transmission includes a hydraulic system for regulating fluid pressure and hydraulic fluid flow in various lines connected to components of the transmission. The system includes a regulator spool valve packaged in a main control casting, which is machined at a transmission production plant. The casting, preferably of an aluminum alloy, is usually referred to as a valve body. The components of the system are assembled in the valve body and have transfer functions characterized at the plant. 
     A solenoid-actuated regulator valve controls pressure communicated from the valve to a clutch or brake whose state of engagement and disengagement determines the gear in which the transmission operates. 
     Transmissions clutch regulators require a method to provide hydraulic pressure to clutches and brakes for high torque operating conditions such that the required pressure can be delivered independently of the control pressure range suitable for shift control. The separation of static capacity (high torque) and dynamic control pressure ranges is accomplished through use of latch valves. 
     The typical latch valve acts to override the regulation of the clutch regulator by exhausting the feedback pressure at the spool. This causes the spool to no longer be in force equilibrium, resulting in spool traveling to its limit opening full communication between supply and control pressure ports. The exhaust of the feedback port and subsequent valve travel result in significant delay and undershoot in clutch control pressure on transition back to dynamic pressure control state. 
     A need exists in the industry for a latch valve formed in a valve body and operating with a regulating valve such that shift control of a transmission control element can be separated from the high pressure that is used to produce the high torque transmitting capacity of the control element when the element is engaged, which will eliminate deficiencies associated with altering regulator feedback pressure, and can be used in conjunction with self-contained devices such as direct acting solenoids. 
     SUMMARY OF THE INVENTION 
     A latch valve includes a first port for containing line pressure, a second port for containing control pressure, a third port located between the first and second ports, alternately connecting the first and second ports to a transmission control element, and a fourth port for containing control pressure that tends to close the second port and open the first port in opposition to a spring force. 
     A method for operating the latch valve includes supplying line pressure to a first port, supplying control pressure to a second port, alternately connecting the first and second ports to a transmission control element through a third port located between the first and second ports, controlling the valve using control pressure tending to close the second port and open the first port in opposition to a spring force, and latching the valve when the first port opens and the second port closes. 
     A multiplexing latch valve that can continue to move throughout the pressure range of the regulator valve doubles as a compliance source to stabilize the regulator valve when the transmission control element is not connected to the regulator valve. This combination maintains the regulator valve in a pressurized state with normal feedback even when the control element is latched to line pressure. 
     The latch valve is actuated by regulator control pressure to selectively connect either regulator control pressure or line pressure to the control element. 
     The multiplexing architecture can be applied to either a variable bleed solenoid (VBS) regulator valve paired systems or to direct acting solenoid systems. For the direct acting solenoid system, latch occurs without the addition of another solenoid, either to supplement the force of the primary solenoid coil or as an On-Off control of a similar multiplexing latch valve. 
     The latch valve provides circuit compliance to stabilize the regulator valve after it is disconnected from the clutch, thereby eliminating need for a separate accumulator part. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a cross section of a casting-integrated direct acting regulating solenoid valve and a latch valve; 
         FIG. 2  is a cross section of a modification of the valve of  FIG. 1  with the spool removed from the valve chamber; 
         FIG. 3  is a cross section of a casting-integrated direct acting regulating solenoid valve showing the spool located in the valve chamber; 
         FIG. 4  is a graph of control element pressure and solenoid current during engagement of the control element; and 
         FIG. 5  includes graphs of delatch pressure and regulating spool position while the latch valve is delatched. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The casting-integrated, direct acting solenoid hydraulic valve  10  shown in  FIGS. 1 and 2  includes a valve body  12  formed of cast metal, preferably an aluminum alloy. The valve body  12  contains a valve spool  14 , formed with lands  16 - 19 ; a compression spring  20  urging the spool rightward; an adapter  22 ; an armature pin  24  extending through the adapter and contacting the spool; an electromagnetic solenoid  26 , which actuates the pin to move leftward when the solenoid is energized and allows the spool to move rightward when the solenoid is deenergized; and a second compression spring  28  for maintaining the pin in contact with the spool. 
     Preferably spring  20  has a relatively low spring constant so that control pressure produced by valve  10  is substantially zero when no electric current is supplied to energize the solenoid  26 . 
     The valve body  12  is formed with control ports  30 ,  42  through which control pressure communicates with the chamber  32  containing the spool  14 ; a line pressure port  34 , through which line pressure communicates with the chamber; sump port  36 , through which hydraulic fluid flows from the chamber to a low pressure sump; and a exhaust ports  38 ,  40 , through which the chamber  32  communicates with a low pressure exhaust. 
     Adapter  22  is continually held in contact with an installation datum or reference surface  46  formed in sump port  34  by the elastic force produced by a resilient clip  44 , which is secured to the outer surface of a housing  45  that encloses the solenoid  26 . 
     In operation, valve  10  regulates control pressure in port  30  and feedback pressure in port  42  by producing a first sum of the force of spring  20  and the rightward net force due to control pressure in port  42  acting on the differential areas of lands  16  and  17 . Balancing the first sum of forces is a second sum of leftward forces comprising the force of the solenoid-actuated pin  24  and the force of spring  28 . As the force of pin  24  increases, valve  10  opens a connection through metering edge  49  between line pressure in port  34  and control pressure in ports  30 ,  42 . As metering edge  49  open, control pressure increases. When control pressure increases sufficiently for the current position of pin  24 , the differential feedback control pressure on lands  16 ,  17  causes the metering edge  49  to close and metering edge  48  to open a connection between control pressure port  30  and to the low pressure exhaust through chamber  32 , exhaust port  38  and passage  72 . 
     A single flycutting tool concurrently machines both of the metering edges  48 ,  49  and the installation datum or reference surface  46  in the valve body. The solenoid module  50  includes adapter  22 , solenoid  26 , housing  45  and spring  28 . 
     All edges that requiring precise relative positions are cut in a single operation for improved tolerances and manufacturing efficiency. Metering edges are precision machined rather than cast for improved edge quality, location accuracy, and zero draft. High precision tolerances enable close control of leakage and pressure regulation accuracy. Close tolerances enable flow control with a short stroke magnetic section  50 . 
     A single metering control pressure port  30  at spool land  18  (Meter Out-Meter In, as shown in  FIG. 1 ) or dual metering control pressure ports  30 ,  38  at control land  52  (Meter Out-Meter Out, as shown  FIG. 3 ) can be accommodated with no change in tolerances. A clear division of tolerance responsibility is established for the two manufacturing groups. 
     The valves shown in  FIGS. 1-3  enable standard main control (multi-bore including worm trail) configurations while providing magnet interface tolerances. 
     A control pressure bleed port  38  provides for spool position control and stability. Tracking response is improved with no dead-zone to cross. Low frequency hunting across the dead-zone is also prevented. 
     Tight machining tolerances allow for minimized overlap reducing dead band. 
     In  FIG. 2  the diameter of control land  17  is larger than the diameter of land  16  of valve  10 ′. The large diameter land  16  of valve  10 ′ defines a large diameter spool end damper  60  for enhancing stability, permitting use of a relatively large diameter, contamination resistant damper port  62 . Damper  60  is formed outside of the feedback path  64  for minimum feedback lag and improved stability. The diameter of damper  60  is large relative to the difference in diameter of the lands  16  and  17 . 
     The large diameter of spool land  16  and damper  60  combined with flow notches enables high flow with short stroke magnet as well as fly cut manufacturing technique. 
     The axial surface  68  of adapter  22  is located in chamber  32  due to contact with reference surface  46  such that, when solenoid  26  is deenergized and spool  14  moves rightward in the chamber, land  19  contacts surface  68  before the armature pin  24  contacts a stop surface  70  in the solenoid module, thereby preventing spring  28  from becoming fully compressed due to contacts among its coils. In this way, the spool end feature provides positive stop for forced over travel protection of the solenoid module  50 . 
     Damping chamber  60  is provided with an oil reservoir using an elevated vent  66  and fed from the control pressure bleed port  42 . 
     The casting-integrated, direct acting solenoid hydraulic valves  10 ,  10 ″ each includes a latch valve  80  formed in the valve body  12  of cast metal. Valve  80  includes a spool  82 , formed with lands  84 ,  86 ; a compression spring  87  urging spool  82  rightward; exhaust port  88 ; line port  90 , connected to a source of line pressure whose magnitude is substantially constant; an outlet port  92 , through which a clutch or brake  94  of the transmission is actuated; a control port  96  communicating through passage  64  with control pressure ports  30 ,  42  of regulator valve  10 ; and a control pressure feedback port  98  also communicating through passage  64  with control pressure ports  30 ,  42  of regulator valve  10 . 
     In operation, valve  80  supplies actuating pressure through line  100  to the cylinder  102  of a hydraulic servo that actuate the transmission control element  94 . When control pressure generated force is lower than spring installed load, spring  87  forces spool  82  to the right-hand end of the chamber, thereby closing line port  90 , opening control port  96  and communicating fluid at control pressure to the control element  94  through outlet port  92  and line  100 . As control pressure increases, spool  82  moves axially leftward along the valve chamber due to a force produced by control pressure in feedback port  98  acting in opposition to the force of spring  87 . After the clutch is fully engaged and control pressure increases further land  86  gradually closes port  96 , and land  84  maintains line port  90  closed. As control pressure increases further, land  86  closes control port  96 , and land  84  opens a connection between line port  90  and output port  92 , thereby bypassing valve  80  and pressurizing control element  94  using line pressure, which is based on static capacity of applied clutches. If control pressure increases further after valve  80  is latched, line pressure alone is applied to fully engage the control element  94 . The spool  14  of regulating valve  10  is maintained in its regulating position while valve  80  is latched. 
     Valve  80  is delatched by reducing control pressure, which causes land  84  to close line port  90 , and land  86  to reopen a connection between control port  96  and the transmission control element  94  through outlet port  92  and line  100 . 
       FIG. 4  shows the variation of outlet pressure in port  92  in response to current in solenoid  26 . The first portion of the relation occurs as control pressure is increased while control port  96  is connected to outlet port  92  and line port is closed. The second portion  106  occurs after point  108  where control port  96  closes and constant line pressure through port  90  opens to outlet port  92  bringing the control element to full capacity at  110 . The two portions allow for increased pressure to current resolution (reduced gain) while maintaining overall achievable pressure range, as seen when compared variation of system without latch feature. 
     The feedback chamber  102  of valve  80  is not exhausted when valve  80  is latched, thereby eliminating the possibility of entrapping air in the lines feeding control element  94 . Because the feedback chamber  102  of valve  80  is not exhausted when valve  80  is latched, those lines need not be refilled when valve  80  is delatched. 
     The regulator valve  10  and latch valve  80  in combination provide functional advantages in transition states of clutch control by performing the latch transition while maintaining regulation control. As  FIG. 5  shows, upon delatching valve  80 , the position  112  of spool  14  of the regulator valve  10  remains in a control metering position because its spool was regulating to the deadheaded circuit  96  and compliance volume  98  while latched and provides superior transition when switched to regulating to the line  100  and control element  94  compared to a VBS-regulator-latch valve system  114 . 
     A VBS-regulator-latch system commonly experiences pressure undershoots  116  past the desired delatch pressure  118 , whereas the delatch pressure transient  120  produced by the combination of valves  10 ,  80  closely tracks the desired delatch pressure  118  with virtually no undershoot. 
     The latch valve is applicable to both VBS/VFS actuated spool valves and direct acting solenoid controlled systems. 
     In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.