Abstract:
The present invention provides a flow accumulator and a clutch control system for an automatic transmission. The flow accumulator includes a dual area piston disposed in a complementary dual diameter cylinder. The small end of the piston is pressurized by fluid from a spool valve which supplies and exhausts fluid to the clutch. The large end of the piston displaces fluid into the clutch when the small end is pressurized. A flow restricting orifice is disposed in parallel with the flow accumulator between the spool valve and the clutch and a pair of check valves control fluid flow into and out of the larger diameter cylinder.

Description:
FIELD 
       [0001]    The present disclosure relates to a clutch control system for automatic transmissions and more particularly to an accumulator and clutch control system for automatic transmissions. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0003]    In most modern automatic transmissions, hydraulic assemblies are filled and exhausted to engage and disengage various clutches and brakes to connect or release various gear components to selectively achieve a plurality of forward speeds or gear ratios and reverse. 
         [0004]    One of the long recognized means of improving inter-ratio gear shifts, and one upon which there is much current emphasis, is to increase the speed of a shift, that is, to reduce the time between release of the currently engaged clutch(es) or brake(s) and engagement of the clutch(es) or brake(s) associated with the selected, new gear ratio. 
         [0005]    One of the ways to increase shift speed is to increase fluid pressure and flow by increasing the size of the pump within the transmission. Any increase in pump size is accompanied by increased energy consumption and thus reduced overall efficiency of the transmission. Although important, compromising the efficiency of the transmission for shift events that occur during a small fraction of its operating time is not a readily acceptable tradeoff. 
         [0006]    The present invention is directed to a device which provides improved shift speeds without the performance compromises accompanying prior solutions. 
       SUMMARY 
       [0007]    The present invention provides a flow accumulator and a clutch control system for an automatic transmission. The flow accumulator includes a dual area piston disposed in a complementary dual diameter cylinder. The small end of the piston is pressurized by fluid from a spool valve which supplies and exhausts fluid to the clutch. The large end of the piston displaces fluid into the clutch when the small end is pressurized. A flow restricting orifice is disposed in parallel with the flow accumulator between the spool valve and the clutch and a pair of check valves control fluid flow into and out of the larger diameter cylinder. When the spool valve moves to provide hydraulic fluid to the clutch to engage it, fluid pressure on the small end of the piston displaces a larger volume of fluid by the large end of the piston to rapidly bring the clutch surfaces into engagement. As the fluid pressure continues to increase, the clutch surfaces engage and transmit torque. When the spool valve moves oppositely to release the clutch, fluid pressure in the clutch reduces and a first check valve inhibits reverse flow into the larger diameter cylinder while a second check valve allows fluid from an exhaust circuit to refill the larger cylinder. A flow accumulator according to the present invention increases clutch activation speed by increasing low pressure, i.e., initial, flow to a clutch and allows downsizing of the hydraulic pump or reduced energy consumption if this is a more desirable design goal. 
         [0008]    Thus it is an object of the present invention to provide a flow accumulator for a clutch in an automatic transmission. 
         [0009]    It is a further object of the present invention to provide a flow accumulator for an automatic transmission clutch utilized with a flow controlling spool valve. 
         [0010]    It is a still further object of the present invention to provide a flow accumulator for an automatic transmission clutch disposed in parallel with a flow control orifice. 
         [0011]    It is a still further object of the present invention to provide a flow accumulator for an automatic transmission clutch having a pair of check valves. 
         [0012]    It is a still further object of the present invention to provide a flow accumulator for an automatic transmission clutch having a dual area piston. 
         [0013]    Further objects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0014]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0015]      FIG. 1  is a schematic diagram of a flow accumulator according to the present invention in a hydraulic clutch circuit of an automatic transmission, and 
           [0016]      FIGS. 2A ,  2 B,  2 C and  2 D are graphs illustrating various fluid pressures, piston displacement, fluid flows and force during operation of a fluid accumulator according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0018]    With reference to  FIG. 1 , a flow accumulator according to the present invention in a hydraulic clutch circuit of an automatic transmission is illustrated and generally designated by the reference number  10 . The flow accumulator  10  includes a stepped or dual diameter housing or cylinder  12  defining a first smaller diameter region  14  and a second larger diameter region  16 . The first smaller diameter region  14  is accessible through a first inlet port  18 . The second larger diameter region  16  is accessible through a first check valve  22  and an inlet or refill port  24 . The first check valve  22  is configured to allow fluid flow from an exhaust feed line into the second larger diameter region  16  but not out of it. The second larger diameter region  16  is also accessible through a second check valve  26  and outlet or exhaust port  28 . The second check valve  26  is configured to allow fluid flow out of the second larger diameter region  16  but not into it. The first and second check valves  22  and  26  may be any suitable type of one-way flow valves such as the ball type check valves illustrated, a flapper valve or a poppet valve. A stepped or dual diameter piston  30  is slidingly disposed within the stepped or dual diameter housing or cylinder  12  and a first compression spring  32  is disposed within the second larger diameter region  16  and biases the dual diameter piston  30  toward the first inlet port  18 . 
         [0019]    A spool valve  40  includes a generally cylindrical housing  42  which slidingly receives a valve spool  44 . The valve spool  44  includes a plurality of spools or lands  46 . The cylindrical housing  42  defines an inlet port  48 , a supply port  52  which communicates with a branching supply line  54  and an exhaust port  56 . The inlet port  48  is connected to a source of pressurized hydraulic fluid or oil such as a gear or gerotor pump  50  which may include a pressure regulator within the automatic transmission. One branch of the supply line  54  communicates with the first inlet port  18  of the flow accumulator  10 . Another branch of the branching supply line communicates through a first flow restricting orifice  58  with a first control port  62  at one end of the housing  42  of the spool valve  40 . A second compression spring  64  aligned with an end of the valve spool  44  biases the valve spool  44  away from the first control port  62 . 
         [0020]    A second control port  66  at the end of the cylindrical housing  42  opposite the first control port  62  receives pressurized hydraulic fluid from a first solenoid control valve  70  when it is energized and a third control port  72  adjacent the second control port  66  receives pressurized hydraulic fluid from a second solenoid control valve  80  when it is energized. Energization of the solenoid control valves  70  and  80  and supply of pressurized hydraulic fluid to the second and third control ports  66  and  72  controls or adjusts the axial position of the valve spool  44  and the lands  46  and thus whether pressurized hydraulic fluid is supplied from the inlet port  48  to the supply port  52  or whether hydraulic fluid in the supply port  52  and the branching supply line  54  is exhausted out the exhaust port  56 . 
         [0021]    In the branching supply line  54 , in parallel with the flow accumulator  10  is a second flow restricting orifice  84 . On the side of the second flow restricting orifice  84  opposite the spool valve  40 , the second check valve  26  and outlet or exhaust port  28  communicate with the branching supply line  54 . The branching supply line  54  terminates in a cylinder  88  of a piston and cylinder assembly  90  associated with a clutch or brake  92  of an automatic transmission (not illustrated). It will be appreciated that the automatic transmission may be, for example, a multiple planetary gear type, a dual clutch type or other configuration of automatic transmission and that the clutch or brake may be any type, for example, a plate or friction pack clutch or band or friction pack brake utilized in such a device. 
         [0022]    The operation of the flow accumulator  10  will now be described. Energization of the second solenoid control valve  80  provides pressurized hydraulic fluid or oil to the valve spool  44  and translates it to the right in  FIG. 1  to open the inlet port  48  and supply pressurized fluid to the outlet port  52  and the branching supply line  54 . The orifices  58  and  84  provide controlled flow restrictions that create a pressure in this portion of the branching supply line  54  higher than on the downstream side of the orifices  58  and  64 . The hydraulic pressure on the smaller face of the dual diameter piston  30  causes it to translate away from the inlet port  18 . The first check valve  22  closes and the second check valve  26  opens to allow a relatively large volume of hydraulic fluid or oil to flow out of the second larger diameter region  16 , into the branching supply line  54  and into the cylinder  88  of the piston and cylinder assembly  90 . As the pressure in the branching supply line  54  continues to increase, the second check valve  26  will close, blocking flow into the second larger diameter region  16  of the dual diameter cylinder  12 , maximum pressure will be applied to the clutch or brake  92  to fully engage it and pressure will build up at the first control port  62  and translate the valve spool  44  to the left to begin to close off the inlet port  48 . 
         [0023]    It should be appreciated that although the hydraulic fluid or oil initially filling the cylinder  88  is at a lower pressure than that nominally delivered by the pump  50  and that necessary to fully engage the clutch or brake  92 , it is sufficient to translate the piston and clutch or brake  92  into incipient engagement, that, is, to translate these components from an at rest, disengaged position to a position just short of full engagement after which there will be little additional movement but there will be significant increase in the pressure applied to the clutch or brake  92  to fully engage it. Accordingly, the flow accumulator  10  reduces the flow demand necessary to fill the cylinder  88  within an acceptable time. This benefit can be enjoyed either by utilizing the faster clutch fill and response time, by reducing the size and output flow of the hydraulic pump  50  or by a weighted compromise between these two operating parameters. It should also be appreciated that although the foregoing discussion has described engagement or activation of a clutch or brake  92  that in its relaxed or quiescent state is not transmitting torque, it is equally applicable to disengagement of such a device which is normally carrying torque and is activated to terminate the transmission of torque. 
         [0024]    To release the clutch or brake  92 , the solenoid valve  80  is de-energized and the fluid pressure at the first control port  62  and the force of the second compression spring  64  translates the valve spool  44  further to the left to close off the inlet port  48  and open the exhaust port  56 . Fluid pressure in the branching supply line  54  drops, the first check valve  22  opens, the second check valve  26  remains closed, the first compression spring  32  translates the dual diameter piston  30  toward the inlet port  18  and the second larger diameter region  16  once again fills with fluid from the first inlet or refill port  24  which may be supplied with fluid from the exhaust port  56 . The second larger diameter region  16  of the flow accumulator  10  according to the present invention is now filled with fluid and is ready to repeat the cycle when engagement of the clutch or brake  92  is commanded. 
         [0025]    Referring now to the graphs of  FIGS. 2A ,  2 B,  2 C and  2 D, they illustrate various relationships between hydraulic pressures and displacement during an operating cycle of the flow accumulator  10  described directly above. In  FIG. 2A , as in all  FIGS. 2B ,  2 C and  2 D, the X axis (abscissa) is time. In  FIG. 2A , the Y axis (ordinate) is relative pressure. The solid line represents pressure regulator output pressure and the dashed line represents the pressure in the piston and cylinder assembly  90 .  FIG. 2B , in synchronism with  FIG. 2A , presents the displacement of the dual diameter piston  30 .  FIG. 2C , also in synchronism with  FIG. 2A , presents flows: the solid line represents the total flow to the piston and cylinder assembly  90 , the dashed line represents the flow from the accumulator  10  and the dotted line represents flow directly from the pressure regulator and the pump  50 .  FIG. 2D , also in synchronism with  FIG. 2A , presents the force applied to the clutch or brake  92 . Note that the pressure in the piston and cylinder assembly  90  and the force exerted by it on the clutch or brake  92  essentially begins to rise only after the flow of hydraulic fluid or oil (see  FIG. 2C ) has ceased. Thus, the significant fluid flow which is necessary to achieve incipient engagement of the clutch or brake  92  is at low pressure and is provided by the flow accumulator  10  of the present invention. 
         [0026]    The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention and the following claims.