Abstract:
A system controlling gain in a control element includes a source of line pressure, a source of signal pressure, a control valve that controls communication between line pressure and the control element, including a first differential area communicating with control element pressure, and a second differential area, and a gain control valve that opens and closes communication between control element pressure and the second differential area in response to signal pressure.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to controlling gain of the hydraulic pressure applied to the servos that engage and release transmission clutches and brakes. 
     2. Description of the Prior Art 
     Automatic transmissions that employ planetary gearing often use the same shift control element, i.e., friction brake or friction clutch, to produce gearshifts among multiple transmission gear ratios. Necessarily, the gain of the hydraulic pressure used to produce the torque capacity of each clutch or brake will be different depending on which gear is applied. 
     In order to achieve smooth gear shifting, hydraulic gain management is used to provide optimum torque capacity of the respective shift control element. For example, in six-speed transmissions, gain management for a given clutch is often achieved using the control pressure from a different clutch. 
     In automatic transmissions able to produce a greater number of forward gear ratios, this is difficult to achieve because each clutch is applied in a greater number of gears. A single clutch control pressure cannot provide enough logical information to allow for gain management in transmission having a large number of forward gears. 
     In conventional practice, solenoid and spool valves are controlled by a system wherein the output of the command solenoid is routed to the designated spool valve being controlled, as well as to a shift valve. The shift valve is used to selectively route solenoid pressure to an additional area on the spool valve, thereby increasing the area on which solenoid pressure acts, resulting in a change in valve gain, i.e., the output/signal pressure ratio. The shift valve in these systems is controlled by a solenoid dedicated to this purpose. Additional dual gain regulators would then require additional shift valves and shift valve control solenoids. 
     SUMMARY OF THE INVENTION 
     A system controlling gain in a control element includes a source of line pressure, a source of signal pressure, a control valve that controls communication between line pressure and the control element, including a first differential area communicating with control element pressure, and a second differential area, and a gain control valve that opens and closes communication between control element pressure and the second differential area in response to signal pressure. 
     The system uses line pressure control solenoid output pressure as the control signal for clutch gain management. This allows for clutch gain to be managed for each clutch and brake element independently in each gear state. 
     The system provides gain management such that clutch gain is independently selected in each gear state via the line pressure control solenoid without additional hydraulic control elements needed to manage gain selection with multiple clutch elements. A single gain control valve is used for multiple dual gain regulators, without the addition of added gain controlling hardware, such as solenoids. 
     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 
         FIG. 1  is a schematic diagram of a system for managing hydraulic gain. 
     
    
    
     The invention will be more readily understood by reference to the following description, taken with the accompanying drawing, in which the FIGURE is a schematic diagram showing a hydraulic gain selection system. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The hydraulic gain selection system  10  includes a clutch control valve  12 , which is actuated by a solenoid  14  to produce a clutch-apply pressure carried in hydraulic line  16  to a clutch  18  of an automatic transmission. Similarly clutch control valve  20  is actuated by a solenoid  22  to produce clutch-apply pressure carried in hydraulic line  24  to another clutch  26  of the transmission. 
     A gain control valve  28  includes a spool  30 , which is urged by a compression spring  32  to move to the left-hand side of a valve bore, in which the spool and spring are located. 
     A fluid pressure signal output from a line pressure control valve  36  is carried in hydraulic line  38  to gain control valve  28 . Line pressure control valve  36  is actuated by a solenoid  40 . Signal pressure acting on the spool  30  of valve  28  produces a force on the spool that acts rightward in opposition to the force of spring  32 . 
     Fluid at regulated line pressure is carried from a line pressure source  41  in hydraulic lines  42 ,  44  to clutch control valve  20  and in lines  42 ,  46  to clutch control valve  12 . 
     Clutch control valve  12  includes a spool  50  formed with lands having unequal cross-sectional areas on which pressure is applied. 
     In operation, the system  10  produces low gain and a clutch-apply pressure in clutch  18  to an upper limit of about 100 psi. by applying to solenoid  14  electric current, preferably in the range between 0-1 amps. While low gain is produced, line pressure is at a relative low magnitude, such that the spool  30  of gain control valve  28  is located at the left-hand end of the valve due to the force of spring  32 . 
     Solenoid  14  opens a connection between ports  52 ,  54 , thereby directing fluid at clutch-apply pressure to clutch  18  through lines  56  and  16  and to port  58  of valve  12 . Clutch-apply pressure at port  58  acts on the larger area of land  60  and smaller area of land  62 , thereby producing a first differential pressure force on spool  50  tending to oppose the force of solenoid  14 . 
     Clutch-apply pressure is carried in lines  56  and  64 , through gain control valve  28  and in line  66  to port  68  of valve  12 . Clutch-apply pressure acts on the larger area of land  62  and the smaller area of land  70 , thereby producing a second differential pressure force on spool  50  tending to oppose the force of solenoid  14  and to maintain gain at the lower magnitude. 
     The system  10  produces high gain and a clutch-apply pressure in clutch  18  of about 200 psi. while solenoid  14  is energized with electric current. While high gain is produced, line pressure is at a relative higher magnitude causes the spool  30  of gain control valve  28  to move rightward against the force of spring  32 , thereby closing communication between lines  64  and  66 , removing the second differential pressure force from spool  50  of valve  12 , opening the throttled communication between ports  52  and  54  of valve  12 , thereby increasing the magnitude of clutch-apply pressure supplied to clutch  18 . 
     In a similar way operation, the system  10  produces low gain and a clutch-apply pressure in clutch  26  to an upper limit of about 100 psi. by applying to solenoid  22  electric current, preferably in the range between 0-1 amps. While low gain is produced, line pressure is at a relative low magnitude, such that the spool  30  of gain control valve  28  is located at the left-hand end of the valve due to the force of spring  32 . 
     Solenoid  22  opens a connection between ports  52 ,  54 , thereby directing fluid at clutch-apply pressure to clutch  26  through lines  72  and  16  and to port  58  of valve  20 . Clutch-apply pressure at port  58  acts on the larger area of land  60  and smaller area of land  62 , thereby producing a first differential pressure force on spool  50  tending to oppose the force of solenoid  22 . 
     Clutch-apply pressure is carried in lines  72  and  74 , through gain control valve  28  and in line  76  to port  68  of valve  20 . Clutch-apply pressure acts on the larger area of land  62  and the smaller area of land  70 , thereby producing a second differential pressure force on spool  50  of valve  20  tending to oppose the force of solenoid  22  and to maintain gain at the lower magnitude. 
     The system  10  produces high gain and a clutch-apply pressure in clutch  26  of about 200 psi. while solenoid  22  is energized with current. While high gain is produced, line pressure is at a relative higher magnitude causes the spool  30  of gain control valve  28  to move rightward against the force of spring  32 , thereby closing communication between lines  74  and  76 , removing the second differential pressure force from spool  50  of valve  20 , opening the throttled communication between ports  52  and  54  of valve  20 , thereby increasing the magnitude of clutch-apply pressure supplied to clutch  26 . 
     Although the system and control method have been described with reference to hydraulic gain control of transmission clutches, the system and control can be applied also to hydraulic gain control of transmission of brakes and to gain control of components other than those of transmissions. 
     Fundamental to gain selection on clutch control valve is that higher gain provides the ability to attain higher pressures in the servos of clutches and brakes. In order to achieve these higher pressures, higher system line pressures are generally required. The system takes advantage of this inherent overlap between line pressure and high gain conditions to use the line pressure command solenoid as the signal device for the gain control valve. 
     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.