Patent Abstract:
A system for controlling hydraulic fluid supplied to a torque converter of an transmission includes a torque converter including a chamber containing an impeller and a turbine, and a bypass clutch having a variable torque capacity, a source of variable control pressure, a latch valve changes in response to the variable control pressure alternately between an unlatched state, wherein the latch valve produces a low pressure output, and a latched state, wherein the latch valve produces a high pressure output, a first valve for limiting hydraulic pressure in the chamber alternately at two magnitudes of pressure in response to the low pressure output and the high pressure output, and a second valve responsive to the variable control pressure for regulating a magnitude of hydraulic pressure that actuates the bypass clutch and changes the torque capacity of the clutch.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a torque converter for an automatic transmission, and, in particular, to a hydraulic system that supplies oil to the converter, actuates an impeller clutch of the torque converter and provides a continuous supply of hydraulic lubricant to transmission components. 
     2. Description of the Prior Art 
     A torque converter is a modified form of a hydrodynamic fluid coupling, and like a fluid coupling, is used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load. A torque converter is able to multiply torque when there is a substantial difference between input and output rotational speed, thus providing the equivalent of a reduction gear. 
     A torque converter includes at least three rotating elements: an impeller, which is mechanically driven by the prime mover; a turbine, which drives the load; and a stator, which is interposed between the impeller and turbine so that it can alter oil flow returning from the turbine to the impeller to multiply torque. The stator is mounted on an overrunning clutch, which prevents the stator from counter-rotating the prime mover but allows for forward rotation. The torque converter is encased in a housing, which contains automatic transmission fluid (ATF), sometimes referred to as “oil,” “lube” or “lubricant.” 
     Hydrodynamic parasitic losses within the torque converter reduce efficiency and generate waste heat. In modern automotive applications, this problem is commonly avoided by use of a bypass clutch (also called lock-up clutch), which physically links the impeller and turbine, effectively changing the converter into a purely mechanical coupling. The result is no slippage, virtually no power loss and improved fuel economy. 
     Torque converter clutch designs include two basic types, a closed piston design and an open piston design. A closed piston design requires a dedicated hydraulic circuit into the torque converter, which communicates only with the apply side of the clutch piston. When pressure is high, the clutch applies. When pressure is low, the clutch releases. A more uncommon form is to have this circuit on the release side where high pressure releases the clutch and low pressure applies the clutch. 
     When the torque converter is multiplying torque, power loss occurs which significantly increases the temperature of ATF in the torque converter and must be cooled before returning to the transmission. Cooler return oil is usually routed into the transmission lubrication circuit to cool internal clutches, gear sets and bearings. The lubrication circuit is also used to fill or charge balance dams, which are intended to keep disengaged clutch pistons from drifting on when internal rotational speeds increase. 
     Hydraulic system logic that controls a torque converter is responsible for several functions including: 1) supplying the converter with sufficient pressure to keep the converter from cavitating, 2) flowing sufficient oil through the converter to remove heat generated in the torus and clutch, 3) controlling pressure in the lock-up clutch piston, 4) supplying oil to the cooling and lube circuits, and 5) minimizing system pump demand for flow and pressure when not required. Many controls systems do not properly control all of these functions 
     A need in the industry exists to control a closed piston torque converter bypass clutch using a simple valve arrangement, that improves clutch control, reduces converter flow demands without introducing risk to the transmission lubrication system. 
     SUMMARY OF THE INVENTION 
     A system for controlling hydraulic fluid supplied to a torque converter of an transmission includes a torque converter including a chamber containing an impeller and a turbine, and a bypass clutch having a variable torque capacity, a source of variable control pressure, a latch valve changes in response to the variable control pressure alternately between an unlatched state, wherein the latch valve produces a low pressure output, and a latched state, wherein the latch valve produces a high pressure output, a first valve for limiting hydraulic pressure in the chamber alternately at two magnitudes of pressure in response to the low pressure output and the high pressure output, and a second valve responsive to the variable control pressure for regulating a magnitude of hydraulic pressure that actuates the bypass clutch and changes the torque capacity of the clutch. 
     The system includes only two regulator valves instead of three to control converter charge pressure, converter clutch pressure and cooler/lube control, thereby reducing the probability of interactions among the regulators, regulator instability, regulator sticking and pressure variability. 
     The system also allows for independent and adjustable flows for the converter circuit, cooler circuit and the lube circuit. 
     Conventional two-pass and three pass converters send the locked converter oil flow directly to the transmission oil sump. This system saves this oil by sending it a transmission oil cooler and transmission lube circuit, effectively saving energy that would otherwise be required to pump a larger oil volume, allows for lower lug limits, and saves fuel. The flow rate is about two liters per minute in an automatic transmission operating in sixth gear at 1000 rpm, which results in a 33 percent reduction in oil flow to the converter, cooler and lube circuits during lock-up. 
     The system allows tuning of oil flow to the cooler and lube circuits when the converter clutch is locked, hard-locked or modulating torque transmitted between the converter&#39;s impeller and turbine. 
     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 sectional side view of a three-pass torque converter to which the control can be applied; and 
         FIG. 2  is schematic diagram of a hydraulic system for controlling operation of a torque converter, such as that shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is illustrated in  FIG. 1  a torque converter  10 , which is arranged about a central axis  12  and includes an impeller  14 , turbine  16 , and stator  18 . The impeller, stator and turbine are located in a toroidal chamber that defines a toroidal fluid flow circuit, whereby the impeller is hydrokinetically connected to the turbine. The torque converter impeller  14  is driveably connected to an engine or another power source. 
     The stator  18  is secured to, and supported for rotation on a stationary stator support shaft  20 . An overrunning brake  22  anchors the stator to shaft  20  to prevent rotation of the stator during torque multiplication but allows free rotation at higher speeds when the turbine flow pushes the backside of the stator blades. The turbine  16  is secured to a rotating transmission input shaft  24 , which transmits torque to a transmission gear box (not shown). A torque converter housing  26 , surrounding the turbine, impeller and stator, is driveably connected to the crankshaft of an internal combustion engine (not shown) or another power source, such as an electric motor. 
     Located within a torque converter housing  26  is a bypass clutch  28  (sometimes called a lockup clutch) for alternately opening and closing a drive connection between turbine  16  and the impeller  14 . Clutch  28  includes a set of friction discs  30 , secured by internal splines to, and supported on a clutch hub  32  for rotation with the hub; a blocker plate  34 , secured by a snap ring  36  to housing  26 ; and clutch plates  38 , secured by splines to housing  26  for rotation with the housing, each plate interleaved between successive friction discs  30 . Hub  32  is secured to compression-spring, torsional dampers  40 ,  42 , which are arranged in series between hub  32  and the transmission input shaft  24 . 
     A turbine shroud  44 , connected to each blade of turbine  16 , is connected by a series of rivets  48  to a turbine hub  50  and a ring  52 , which is driveably connected though a spline to clutch hub  32 . The output of damper  42  is driveably connected to a damper hub  54 , which is connected by a spline  56  to input shaft  24 . 
     Lockup clutch  28  is actuated by a piston  58 , which is supported for axial displacement along axis  12 . Piston is sealed at its outer periphery by a dynamic seal  60  to an inner surface of housing  26  and is sealed at its inner periphery by a dynamic seal  62 , thereby defining a sealed volume  64  located between piston  58  and housing  26 . When volume  64  is pressurized through clutch apply passage  66  (CAPY), piston  58  moves leftward forcing friction discs  30  and clutch plates  38  into mutual frictional contact, thereby engaging bypass clutch  28 . When clutch  28  is engaged, the engine and turbine  16  are mechanically interconnected and driveably connected to the transmission input shaft  24 . When lockup clutch  28  is disengaged, the turbine  16  and engine are mechanically disconnected, and the turbine is hydrokinetically driven by the impeller  14 . 
     ATF fills the toroidal volume in which the turbine  16 , impeller  14  and stator  18  rotate, at converter charge pressure (CCL) through an annular passage  70  between input shaft  24  and stator support  20 . ATF exits torque converter  10  at converter discharge pressure (COUT) through passage  72 , an annular passage between stator support  20  and a converter drive shaft  76 , on which impeller  14  is supported. 
       FIG. 2  illustrates a hydraulic system for controlling converter charge limit pressure (CCL) of the fluid that enters the toroidal chamber of converter  10  through line  70 , converter apply pressure (CAPY) that controls converter clutch  28 , and fluid exiting the converter (COUT) through line  72 . 
     The torque transmitting capacity of clutch  28  may vary among: (1) a locked condition, in which clutch  28  is applied but may be slipping; (2) a hard locked condition, in which the clutch is applied with zero slip, transmitting full engine torque; (3) a unlocked condition, in which clutch  28  is released and has zero torque capacity; and (4) a modulating condition, in which the clutch is slipping and transmitting a commanded torque equal to or less than engine torque. 
     The hydraulic system includes a converter charge pressure limit valve  80 , which may be a regulator valve or, as shown in  FIG. 2 , a limit valve having no exhaust port. 
     A converter apply pressure regulator valve  82 , a differential regulator valve that regulates pressure and has a second feedback pressure (CRLZ), supplied through a converter release latch orifice AE. 
     A converter charge pressure control latch valve  84  has only two positions, between which it shuttles to hold or latch in either of two pressure magnitudes, which are supplied to valve  82 . 
     Clutch exhaust (CLEX) line  86  keeps oil exhausted out of clutch  28  from draining out, keeping circuit fluid filled for improved consistency and response. Converter-out-to cooler (COTC) flow in line  72  exits the transmission case at  90  to transmission oil cooler  92 , returns to the transmission case at  94  after exiting the cooler, and the cooled ATF flows to a transmission lube circuit  96 , through which bearings, shafts, gears and other mechanical components of the transmission are lubricated. 
     Converter-out-to-exhaust (COTX) line  98  carries ATF to the lube circuit  96 . 
     Converter release latch exhaust pressure (CRLX) is carried in line  88  between ports of valve  80 . Converter release latch orifice pressure (CRLZ) is generated by converter charge pressure control latch valve  84  and is carried in orifice line  99  between valves  80  and  82 . 
     Line Pressure (LP), a first priority output of main regulator  100 , is carried in line  102  to valve  82 . Line pressure exhaust (LPX), a second priority output of main regulator  100 , is carried in line  104  to valve  80 . R: Reverse pressure (R), an output from manual valve  106 , is carried in line  108  to valve  82 . 
     Solenoid feed (SF), a regulated pressure carried in line  110 , is supplied to solenoid  112 , which controls TCC valve  114 . The output of solenoid  114  is torque converter clutch control pressure (TCCZ) carried in orifice line  116  to latch valve  84  and valve  82 . Torque converter clutch control pressure (TCCL), carried in line  118 , is the latched pressure output produced by latch valve  84 . 
     Ball valve (BV 10 ) opens and closes in response to differential pressure caused by COTX and COTC across valve  120 . A converter anti-drain back valve  122  prevents ATF from draining out of converter  10  through line  72 , when engine of off. 
     When clutch  28  is unlocked, solenoid control pressure TCCZ is less than about 7.3 psi, fluid at LPX pressure is supplied to valve  80 , and CRLZ pressure at the end of the spool  138  of valve  80  is zero as a result of its being vented at the VENT port of latch valve  84 . These pressures and the spring of valve  80  move spool  138  leftward from the position shown in  FIG. 2 , thereby opening a connection between LPX pressure and the CRLX passages  88  of valve  80 . The feedback CRLX pressure on land  139  regulates CCL pressure to 100 psi in CCL line  70 , which is connected by valve  80  to the CRLX passage  88 . 
     Therefore, while clutch  28  is unlocked, torque converter  10  is supplied with CCL pressure at about 100 psi from the converter charge pressure limit valve  80 . Flow through the converter  10  is a function of CCL pressure. While clutch  28  is unlocked, oil exiting converter  10  through line  72  flows directly to cooler  92  and the lube circuit  96 . A thermostatic control valve will bypass the cooler  92 , when oil temperature is below 180 deg F., allowing the transmission to warm up faster, thereby reducing viscous drag, improving the transmissions efficiency. This bypass occurs by creating a lower resistance path between circuits COTC  130  and LUBE  96 . Converter apply pressure regulator  82  is not used while clutch  28  is unlocked, and is held off by exhausting CRLZ circuit through the converter charge pressure control valve  84 . Also, when the vehicle operator moves the gear selector to the Reverse position, R pressure in line  108  is fed to the converter apply pressure regulator  82  as an additional force to hold valve  82  off. Although this action is not necessary, it comes without added cost or complexity. Check ball (BV 10 )  120  keeps oil from back flowing from COTC line  130  to COTX line  98 . 
     When clutch  28  is locked, hard locked or modulating, converter charge pressure control valve  84  must latch. Valve  84  is unlatched when TCCZ pressure is less than about 7.0 psi. Valve  84  is latched when TCCZ pressure is greater than about 10.0 psi. The magnitude of electric current supplied to solenoid  112  changes the magnitude of TCCZ pressure produced by valve  114  in response to the current. 
     To latch valve  84 , current supplied to solenoid  112  is increased toward 850 milliamps, which increases pressure TCCZ in line  116  to greater than the reference pressure, 10.0 psi, at which valve  84  latches. As TCCZ pressure increases toward 10 psi, the spool  132  strokes rightward opening a connection between TCCZ line  116  and TCCL line  118 , thereby adding to the pressure force on land  134 , which force opposes the force of spring  136 . 
     When valve  84  latches, CCL pressure line  70  is opened to CRLZ line  99 , and CCL pressure is sent to an addition pressure area on land  138  of the converter charge pressure limit valve  80 , causing valve  80  to reduce CCL pressure in line  70  to about 45 psi. This pressure reduction occurs because converter  10  does not need as much pressure while clutch  28  is locked or modulating, and because increasing the torque capacity of clutch  28  by leftward movement of the converter clutch piston  58  is facilitated by low CCL pressure in the toroidal chamber of converter  10 . 
     When valve  84  latches, CCL pressure is communicated to land  138  of the converter charge pressure limit valve  80  via CRLZ line  99  and to one of two feedback ports of valve  82 , causing the spool  140  of valve  82  to regulate converter apply pressure (CAPY), which is carried in line  66  to the converter clutch  28 . The pressure force effects of the two feedback pressures on valve  82 , CRLZ pressure at 45.0 psi in line  99  and variable TCCZ pressure greater than 10.0 psi in line  116  regulate CAPY pressure, which is carried in line  66  to the converter clutch  28 . 
     When valve  84  latches, the rightward stoking of its spool  132  connects CCL pressure in line  70  to cooler  92  through the COTX circuit line  98 , which is used to supplement flow to the COTC circuit  98  and LUBE circuit  96 , since circuits  98  and  96  will receive less oil from the COUT circuit  72  after valve  84  latches and CCL pressure drops to 45 psi. Flow in COUT circuit  72  is lower because the converter is now being fed oil at 45 psi instead of 100 psi. The diameter of orifices U  142  and SS  144  are sized to produce the correct flow rates in COTC circuit  130  and LUBE circuit  96  during locked and modulating operation of bypass clutch  28 . 
     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.

Technology Classification (CPC): 5