Abstract:
The present invention provides a clutch having two pistons, a first piston defining a first, smaller area and a second piston, defining a second, larger area. The separate pistons are independently provided with flows of pressurized hydraulic fluid from first and second independent modulatable control valves. Engagement of the clutch may be rapid by providing hydraulic fluid to the smaller area piston, provide greater engagement force by providing hydraulic fluid to the larger area piston or a combination of speed and force by utilizing modulated or unmodulated flows of hydraulic fluid to both pistons.

Description:
FIELD 
       [0001]    The present disclosure relates to a clutch having a dual area piston and more particularly to a clutch having two pistons of distinct areas and dual pressure valves for providing independent control of the pressure applied to each piston. The clutch finds particular application in multiple speed automatic transmissions for motor vehicles. 
       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]    A current design class of multiple speed automatic transmissions comprehends a plurality of planetary gear assemblies having their sun gears, planet carriers and ring gears interconnected by permanent connections and selectively connected by clutches or grounded by brakes. The clutched and brakes are generally engaged or activated by hydraulic fluid pressure. 
         [0004]    The speed and force with which the clutches and brakes can, should or must be engaged is a major factor in the performance of such transmissions and is the subject of much study. If speed is the more significant design parameter, the clutch piston can be made smaller such that a typical flow of pressurized fluid will quickly move the piston. On the other hand, if force is more important, the clutch piston may be made larger (have a larger area). While it will obviously not move as quickly, given the same pressurized fluid flow provided to a smaller piston, it will be capable of generating higher force. 
         [0005]    An acknowledged engineering compromise to this problem is a clutch engaged or activated by a dual area piston. The flow of pressurized hydraulic fluid is provided to a modulating control valve and thence to a shift valve which directs the modulated flow of fluid to the selected larger or smaller area of the piston. Thus, by incorporation and control of the shift valve, a single clutch and piston can produce rapid, low force movement utilizing the smaller area of the piston and slower, higher force movement utilizing the larger area of the piston. 
         [0006]    In practice, however, this approach has revealed a shortcoming. In certain shift situations, it is necessary to reposition the shift valve in the middle of a shift. Whenever this is done, the pressure level on one side is immediately transferred to the other. When this occurs during a shift, poor torque capacity control may result. 
         [0007]    Thus it is apparent that improvements in dual area clutches and actuating systems for use in automatic transmissions are desirable. 
       SUMMARY 
       [0008]    The present invention provides a clutch having two pistons, a first piston defining a first, smaller area and a second piston defining a second, larger area. The separate areas of the pistons are independently provided with flows of pressurized hydraulic fluid from first and second independent modulatable control valves. Engagement of the clutch may then be rapid by utilizing the smaller area piston, provide greater engagement force by utilizing the larger area piston or a combination of speed and force by utilizing modulated or unmodulated hydraulic fluid flows to both pistons. Clutch engagement speed and force are also controlled by an orifice disposed in each fluid line between the control valves and the pistons. The dual area clutch and independent control valves of the present invention find particular application in automatic transmissions for motor vehicles in which they may be utilized in association with both clutches and brakes. 
         [0009]    Thus it is an object of the present invention to provide a clutch incorporating dual area pistons and having independent pressure control. 
         [0010]    It is a further object of the present invention to provide a clutch incorporating dual area pistons and dual modulating control valves. 
         [0011]    It is a still further object of the present invention to provide a clutch incorporating dual area pistons and dual modulating control valves which independently control the hydraulic pressure applied to each piston. 
         [0012]    It is a still further object of the present invention to provide a clutch incorporating dual modulating control valves, flow control orifices and dual area pistons. 
         [0013]    It is a still further object of the present invention to provide a clutch incorporating dual area pistons and dual modulating control valves having particular application in automatic transmissions for motor vehicles. 
         [0014]    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 
         [0015]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0016]      FIG. 1  is a diagrammatic view of a multiple speed automatic transmission incorporating the present invention; and 
           [0017]      FIG. 2  is a diagrammatic view of a hydraulic circuit of a clutch or brake having a dual area piston with independent pressure control according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0019]    With reference now to  FIG. 1 , a motor vehicle powertrain is illustrated and generally designated by the reference number  10 . The motor vehicle powertrain  10  includes an engine and torque converter  12 , a multiple speed automatic transmission  14  and a conventional final drive assembly  16 . 
         [0020]    The automatic transmission  14  includes an input shaft  17  connected to the output of the engine and torque converter  12 , a planetary gear configuration  18  and an output shaft  19  connected to the final drive assembly  16 . The planetary gear configuration  18  includes a first planetary gear set  20 , a second planetary gear set  30  and a third planetary gear set  40 . 
         [0021]    The first planetary gear set  20  includes a first sun gear  22 , a first ring gear  24  and a first planet gear assembly  26 . The first planet gear assembly  26  includes a first plurality of planet gears  27  rotatably disposed on a first planet gear carrier  29  and arranged in meshing relationship with both the first sun gear  22  and the first ring gear  24 . 
         [0022]    The second planetary gear set  30  includes a second sun gear  32 , a second ring gear  34  and a second planet gear assembly  36 . The second planet gear assembly  36  includes a second plurality of planet gears  37  rotatably disposed on a second planet gear carrier  39  and arranged in meshing relationship with both the second sun gear  32  and the second ring gear  34 . 
         [0023]    The third planetary gear set  40  includes a third sun gear  42 , a third ring gear  44  and a third planet gear assembly  46 . The third planet gear assembly  46  includes a third plurality of planet gears  47  rotatably disposed on a third planet gear carrier  49  and arranged in meshing relationship with both the third sun gear  42  and the third ring gear  44 . 
         [0024]    The planetary gear configuration  18  also includes a plurality of selectable torque transmitting devices. Two of the torque transmitting devices,  50  and  52 , selectively connect two rotating members and are thus properly characterized as clutches. Four of the torque transmitting devices,  54 ,  56 ,  58  and  59 , selectively ground, i.e., connect to a stationary, a rotating member and are thus properly characterized as brakes or reaction clutches. 
         [0025]    Several of the components of the planetary gear sets  20 ,  30  and  40  are permanently connected to other components. The input shaft  17  is connected to the first sun gear  22 . The output shaft  19  is connected to the to the third ring gear  44 . The first ring gear  24  is connected to the second sun gear  32  through an interconnecting member  70 . The first planet gear carrier  29  is connected to the second planet gear carrier  39  and the third sun gear  42  through an interconnecting member  72 . 
         [0026]    The first sun gear  22  is selectively connected to the third planet gear carrier  49  by a first clutch  50 . The second ring gear  34  is selectively connected to the third planet gear carrier  49  by a second clutch  52 . The first ring gear  24  is selectively grounded to a housing  60  of the transmission  14  by a first brake  54 . The first planet gear carrier  29  is selectively grounded to the housing  60  by a second brake  56 . The second ring gear  34  is selectively grounded to the housing by a third brake  58 . Finally, the third planet gear carrier  49  is selectively grounded to the housing  60  by a fourth brake  59 . 
         [0027]    As noted above, the automatic transmission  14  is capable of providing multiple forward speed, gear and torque ratios by selective engagement, in sequence, of various combinations of the just described clutches  50  and  52  and brakes  54 ,  56 ,  58  and  59 . Such operation is beyond the scope of this patent. Further explanation, however, may be found in U.S. Pat. No. 6,723,019 which is hereby incorporated by reference. 
         [0028]    Turning now to  FIG. 2 , a hydraulic circuit for activating or engaging any of the clutches  50  and  52  and the brakes  54 ,  56 ,  58  and  59  in an automatic transmission  14  is illustrated and designated by the reference number  70 . It should be understood that while primarily intended for use in automatic transmissions, the hydraulic circuit  70  may find broad application in diverse hydraulic device control applications. The hydraulic circuit  70  includes a first solenoid control valve  72  which is supplied with pressurized hydraulic fluid or oil in a line  74 . Hydraulic fluid or oil flows out of the first solenoid control valve  72  in an exhaust or return line  76 . The first solenoid control valve  72  includes a first electromagnetic coil  78 , a first axially, bi-directionally translatable plunger  82  and a first valve spool  84  which, depending upon its axial position, supplies and exhausts hydraulic fluid or oil from a first fluid line or passageway  86  communicating with a first, smaller area clutch or brake activating piston  88  of a dual area piston assembly  90  through a flow control orifice  91 . 
         [0029]    The hydraulic circuit  70  also includes a second solenoid control valve  92  which is supplied with pressurized hydraulic fluid or oil in the line  74 . Hydraulic fluid or oil flows out of the second solenoid control valve  92  in the exhaust or return line  76 . The second solenoid control valve  92  includes a second electromagnetic coil  98 , a second axially, bi-directionally translatable plunger  102  and a second valve spool  104  which, depending upon its axial position, supplies and exhausts hydraulic fluid or oil from a second fluid line or passageway  106  communicating with a second, larger area clutch or brake activating piston  108  of the dual area piston assembly  90  through a flow control orifice  109 . 
         [0030]    The solenoid control valves  72  and  92  are both preferably modulating valves which are commonly referred to as variable bleed solenoids (VBS) which may operate on a pulse width modulated (PWM) signal and include a regulator valve or they may be direct acting (VFS) solenoid valves. Alternatively, the solenoid control valves  72  and  92  may be two position (on-off) valves. 
         [0031]    The dual area piston assembly  90  also includes a housing  110  which receives the first and second pistons  88  and  108  and maintains them in operable alignment with a clutch assembly  52  which is representative of all of the clutches and brakes illustrated in  FIG. 1 . The configuration of the pistons  88  and  108  as well as that of the housing  110  will depend upon the configuration and location of the associated clutch or brake but they will typically be annular with the first, smaller area piston  88  having a smaller nominal diameter which is surrounded by the second, larger area piston  108  which has a larger nominal diameter. 
         [0032]    Disposed between the first and the second lines or passageways  86  and  106  is an optional dual input ball check assembly  114  including a chamber  116  communicating with both the first fluid line or passageway  86  and the second fluid line or passageway  106 . Disposed within the chamber  116  is a ball check  118  and communicating with the chamber  116  is a pressure sensor  120 . The ball check assembly  116  is supplied with hydraulic fluid or oil from both the first and the second fluid lines or passageways  86  and  106  and, because of movement of the ball check  118 , the pressure sensor  120  is subjected to, reads and provides data or a signal in a wire or cable  122  regarding the magnitude of the higher of the two pressures in the first and the second fluid lines or passageways  86  and  106 . The signal from the pressure sensor  120  may be supplied to operating or control devices to provide feedback regarding the higher instantaneous pressure in the fluid lines or passageways  86  and  106  or the signal may be provided to diagnostic devices which ensures proper operation of the dual area piston assembly  90  and provide fault signals, for example. As noted above, however, the dual input ball check assembly  114  is an optional component. 
         [0033]    The dual area piston assembly  90  according to the present invention has four modes of operation: a) utilizing only the first, smaller piston  88 , b) utilizing only the second, larger piston  108 , c) utilizing both the first and the second pistons  88  and  108  and d) utilizing one of the pistons  88  or  108  to engage the clutch  52  and then both of the pistons  88  and  108  to modulate the clutch  52 . The particular mode of operation chosen will be based on shift requirements. For example, a high torque shift may require that both pistons  88  and  108  are modulated together in order to achieve sufficient torque throughput to complete the shift. However, a high torque shift may also require the shortest possible delay before starting the shift. Under the circumstances, mode d) may be chosen in order to minimize delay while providing the required torque capacity. Another example is a low torque shift during which the smaller area piston  88  only is provided with modulated pressure hydraulic fluid. This provides minimum shift delay, maximum resolution and the smallest sensitivity to pressure errors due to, for example, circuit restrictions, overshoot, undershoot, instability and solenoid inaccuracy. 
         [0034]    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.