Abstract:
A method of controlling an upshift in a transmission having a main box and a compounder that has at least one gearset and at least one friction element separate from the main box includes initiating an upshift in the main box including application of at least one friction element (e.g. a clutch) in the main box, and releasing a friction element (e.g. a clutch) in the compounder providing a swap shift. The duty cycles of solenoids associated with the releasing and applying elements may be alternately controlled in open loop and closed loop fashion to improve the quality of the shift.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to vehicle transmissions and more particularly to a method for controlling an upshift in a transmission. 
       BACKGROUND OF THE INVENTION 
       [0002]    An automatic transmission typically includes an electronically controlled hydraulic system. In such an electro-hydraulic system, hydraulically actuated clutches are actuated to couple and decouple gearsets for changing gear ratios of the transmission. Also, a transmission pump supplies pressurized hydraulic fluid from a fluid sump to the clutches through fluid passages. Further, solenoid actuated valves are placed in fluid communication with the fluid passages upstream of the clutches. Finally, a controller receives vehicle input signals, processes the input signals with shift control algorithms to produce solenoid control output signals, and communicates the output signals to the solenoid valves to control flow of fluid to the clutches. 
       SUMMARY OF THE INVENTION 
       [0003]    A method of controlling an upshift in a transmission having a main box and a compounder that has at least one gearset and at least one friction element separate from the main box includes initiating an upshift in the main box including application of at least one friction element (e.g. a clutch) in the main box, and releasing a friction element (e.g. a clutch) in the compounder providing a double swap shift. The duty cycles of solenoids associated with the releasing and applying elements may be alternately controlled in open loop and closed loop fashion to improve the quality of the shift. 
         [0004]    One implementation of a method of controlling a double swap upshift in a transmission having a main box and a compounder coupled to the main box, includes: 
         [0005]    initiating an upshift in the main box; 
         [0006]    determining the end of an upshift torque phase in the main box; 
         [0007]    initiating a downshift in the compounder near the end of the upshift torque phase in the main box so that the speed phase of the downshift in the compounder begins after the speed phase of the upshift begins in the main box; 
         [0008]    determining a compounder target speed for the selected gear into which the transmission is being shifted; 
         [0009]    controlling, after the compounder speed is within a threshold value of the compounder target speed, the solenoid duty cycle associated with the clutch being applied to complete the shift. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The following detailed description of preferred embodiments and best mode will be set forth with regard to the accompanying drawings in which: 
           [0011]      FIG. 1  is a schematic view of one implementation of a transmission; 
           [0012]      FIG. 2  is chart illustrating clutches applied in the transmission of  FIG. 1  in the various gears of the transmission; 
           [0013]      FIG. 3  is a schematic view showing the torque flow in the transmission of  FIG. 1  when it is in second gear; 
           [0014]      FIG. 4  is a schematic view showing the torque flow in the transmission of  FIG. 1  when it is in third gear; and 
           [0015]      FIG. 5  is a graph of various parameters and components of the transmission and related components during execution of an upshift. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]    Referring in more detail to the drawings,  FIG. 1  illustrates a six-speed transmission  10  that includes a main gear box  12  and a compounder  14  arranged in series. In one implementation, the main gear box  12  is disposed between a torque converter  16  having a turbine diagrammatically illustrated at  17 , and the compounder  14 . The main gear box  12  may include gearsets  13 ,  15  and various friction elements, which in one implementation may include clutches such as an underdrive (UD) clutch  18 , overdrive (OD) clutch  20 , reverse clutch (R)  22 , 2-4 clutch  24 , and a low-reverse (L-R) clutch  26 , and associated gear sets. By themselves, the clutches and gearsets of the main box  12  provide a 4-speed transmission assembly that may be generally of the type set forth in U.S. Pat. No. 4,969,098, the disclosure of which is incorporated herein by reference in its entirety. The compounder  14  may include one additional gear set  28 , and associated friction elements such as a LC clutch  30  and a DR clutch  32  with an over-running or freewheel clutch  34 . The freewheel clutch  34  automatically releases or is not engaged when the DR clutch  32  is applied, and when the DR clutch  32  is not applied, the freewheel clutch  34  automatically engages, as is known in the art. With the addition of the compounder  14 , six speed transmission operation can be obtained with double swap shifts. The general construction and arrangement of the transmission  10  is set forth in U.S. Publication No. 2006/0142106, Published Jun. 29, 2006, and this reference is incorporated herein by reference in its entirety, although the double swap upshift control methodology is set forth herein. 
         [0017]    To accomplish six speed transmission operation, a so-called double swap shift is performed to shift the transmission  10  between 2 nd  and 3 rd  gears. In general terms, during the double swap shift an upshift is initiated in the main box  12  and near the end of a torque phase of that upshift a downshift is initiated in the compounder  14 . More specifically, to shift from 2 nd  to 3 rd  gear in this implementation of the transmission  10 , the L-R clutch  26  is released and the 2-4 clutch  24  is applied in the main box  12 , and near the end of the torque phase of the upshift in the main box, the DR clutch  32  is released and the freewheel clutch  34  is automatically grounded. Careful control of this swapshift permits it to be performed smoothly with minimal power loss, bump, or other feedback noticeable by the occupants of the vehicle. 
         [0018]    The solenoids that control application or release of the clutches preferably are, but are not limited to, pulse width modulated (PWM) solenoids and hence, the filling and venting of fluid chambers associated with the solenoids are controlled by controlling the duty cycle of the solenoids. The instantaneous duty cycle of a given solenoid may be provided, communicated or otherwise obtained from a table, list or other source of stored data, or it may be a function of closed loop feedback control from various sensors, a combination of both in a given shift sequence or sequences, or otherwise chosen, determined or selected. The duty cycle at any given time during a shift may be controlled to achieve a certain target or selected volume of fluid in the clutch, which may be related to the pressure and/or torque capacity of the clutch. Such target volume based torque phase control during an upshift is disclosed in U.S. patent application Ser. No. 11/222,066 which was filed on Sep. 8, 2005, and which is incorporated by reference herein in its entirety. 
         [0019]    The element being released is vented so that the fluid pressure therein is reduced to a minimum that will support the torque hand-off to the element being applied. The apply rate for the element being applied is controlled to develop the torque needed to begin the speed change phase just as the release element net-apply-pressure reaches zero. This provides a matched exchange that reduces resistance or fight between the release and apply elements and provides a relatively smooth shift. Once the speed change begins the apply element pressure may be controlled to provide desired acceleration of a torque converter turbine. 
         [0020]    Turning now to one implementation of a double swap shift, some of the time based events and sequence of a 2 nd  gear to 3 rd  gear double swapshift are shown in  FIG. 5 . As shown in  FIG. 2 , prior to initiation of the shift, the UD and L-R clutches  18 ,  26  are applied in the main box  12  and the DR clutch  32  is applied in the compounder  14 . As a result of the shift, the L-R and DR clutches  26 ,  32  are released and the 2-4 clutch  24  and freewheel clutch  34  are applied. By way of further illustration, the torque flow path of the transmission  10  in 2 nd  gear is shown in  FIG. 3 , and the torque flow path of the transmission in 3 rd  gear is shown in  FIG. 4 . In  FIGS. 3 and 4 , the applied clutches and active torque flow paths are shown in solid black, and released clutches are shown lighter grey lines. 
         [0021]    Referring now to  FIG. 5 , at to, the start of the upshift sequence, the 2-4 clutch solenoid  36  ( FIG. 1 ) duty cycle is at 100%, as shown in line  38 , for a fast fill and rapid increase in volume of the 2-4 clutch  24  as shown in line  41 , and some pressure increase as shown in line  40 . The fast fill may begin first because it usually takes more time to fill the clutch volume with the transmission fluid before the clutch develops any noticeable torque capacity than the time needed to completely vent a clutch to its zero torque capacity. The fast fill continues until the filled volume in the 2-4 clutch  24  reaches a learned fill volume that corresponds to a pressure just lower than the pressure where the 2-4 clutch overcomes the return spring force of the clutch piston (which is where the clutch initially has torque capacity), so just before the torque phase in the main box begins. At t 1 , the torque phase of the upshift begins, the fast fill rate of the 2-4 clutch ends and control of the duty cycle of the 2-4 clutch solenoid  36  begins to provide a second, slower fill rate for a more gradual increase in the volume (and hence, pressure) of the 2-4 clutch. In this manner, the solenoid  36  duty cycle may be changed to gradually increase the 2-4 clutch volume to a learned target volume as a function of various parameters including, for example, engine torque, torque converter turbine speed, transmission output speed, and time. The input and output speeds may be measured by sensors  39 ,  41 , respectively, and the compounder speed may be measured by another sensor  43  between the main box  12  and compounder  14 . The solenoid duty cycle in this time interval can be selected from a table and/or a source of learned data. 
         [0022]    Shortly thereafter, at t 2 , venting of the release element (the L-R clutch  26 ) is initiated (as shown by the pressure curve shown in  FIG. 5  at line  45 ) while the pressure of the 2-4 clutch  24  is increased as noted above. It should be noted that, depending on the venting rate or the L-R clutch volume, the venting may be initiated before t 2 . In the example shown herein, the L-R clutch is not associated with an overrunning clutch. If an overrunning clutch is provided, this venting process may not be needed. Venting of the L-R clutch  26  may be started with a ballistic vent rate and may begin after the volume in the 2-4 clutch reaches some threshold level, or based on some other criteria, including as a function of the time required to engage the 2-4 clutch (i.e. the time required for the 2-4 clutch to reach required torque capacity to start the speed change phase of the upshift may be used and compared to the time needed to vent L-R clutch to determine when to initiate venting of the L-R clutch so it reaches zero torque capacity just before the 2-4 clutch has reached the required torque capacity to start the speed change phase). As shown by lines  44 ,  46 , torque converter turbine speed and compounder speed may remain relatively constant to this time. At t 3 , venting of the DR clutch  32  in the compounder  14  is initiated, as shown by the duty cycle change in line  48  and the pressure decrease in line  50 . At t 4 , a soft or slower release of the DR clutch  32  is initiated when the DR clutch  32  reaches a learned volume selected to permit slip in the compounder at a desired time. Accordingly, the DR clutch  32  is vented at a first rate which may be a fast or ballistic rate until a soft release start volume is reached and then venting continues at a second, lower rate until slippage occurs in the compounder as will be discussed. The volume at which the soft release is started is based at least in part on the turbine output torque and transmission output speed and may be a learned value that can be adjusted as a function of conditions sensed in prior shifts (for example, the time interval between the start point of the speed phase in the main box and the start point of the speed phase in the compounder compared to a desired time interval). The soft release is initiated by moderating the duty cycle of the DR clutch solenoid  54  (as shown in  FIG. 1  and line  48 ) to slow the rate at which it is vented so that its volume is decreased to a level that corresponds with a pressure (as shown in line  50 ) just above the required torque capacity to prevent slip in the DR clutch. Turbine speed and compounder speed can remain relatively constant. 
         [0023]    At t 5 , and as shown in line  44 , the torque converter turbine speed changes indicative of slip of the L-R clutch in the main box. In other words, the turbine speed is less than the compounder speed times the gear ratio in the main box which means the L-R clutch slips after the 2-4 clutch takes over all capacity. If the turbine speed is higher than the compounder speed times the gear ratio in the main box, the L-R clutch slips before the 2-4 clutch reaches its target volume (or required torque capacity). If that happens, the L-R clutch would momentarily be reapplied to hold the turbine speed, which is so-called “bump along”, as set forth in U.S. Pat. No. 4,969,098. At this time the speed or inertia phase of the upshift in the main box begins and the torque phase ends. The duty cycle of the 2-4 clutch solenoid could be utilized to bring the turbine speed to a desired acceleration, and that could be accomplished at this point with feedback control. In some applications, though, the time until the next control phase (e.g. the time between t 5  and t 6 ) may be too short to effectively utilize feedback control. 
         [0024]    As the turbine decelerates, the torque input to the compounder increases which triggers the DR clutch slip. If this slip occurs later than desired, the learned soft release start volume used to initiate the soft release of the DR clutch at t 4  can be decreased. If the slip occurs earlier than the speed phase begins at the main box, the learned soft release start volume at which the soft release is initiated can be increased. In this manner, the system can accommodate and adjust as various factors cause changes in transmission operation over time. 
         [0025]    At t 6 , the compounder speed begins to increase (as shown in line  46 ) as the DR clutch  32  slips, and this marks the beginning of the speed phase in the compounder. Hybrid feedback control of the DR clutch solenoid  54  duty cycle is initiated and a fixed apply element volume instead of the feedback control or a feed forward control method may be used in the main box when the compounder speed change is detected. Hybrid feedback control of the DR clutch solenoid  54  duty cycle may be accomplished as a function of feedback from sensors that detect engine torque, turbine speed, compounder speed and transmission output speed, as examples, to achieve a desire acceleration. As shown, the duty cycle of the DR clutch solenoid  54  may be increased to increase the fluid volume and pressure in the DR clutch  32  or decreased to decrease fluid volume and pressure in the DR clutch to control the compounder acceleration to a desired or determined rate. As is known in the art, slippage in the compounder may be detected as a function of the input and output speeds, and the gear ratio. If the input speed at the compounder  14  is equal to the compounder output speed times the gear ratio in the compounder  14 , there is no slippage in the compounder. If the compounder input speed is greater than the compounder output speed times the gear ratio in the compounder, there is slippage in the compounder. If the rate of slippage speed increase is greater than a designed or desired slippage rate, the DR clutch pressure can be increased (by increasing the duty cycle of its solenoid to increase the fluid volume in the DR clutch). If the slippage rate is lower than the desired slippage rate, the DR clutch pressure can be decreased. 
         [0026]    At t 7 , as the compounder speed nears or is within a threshold value of its target speed (determined as a function of the selected gear into which the transmission is being shifted), feedback control of the 2-4 clutch solenoid  36  duty cycle is resumed and the DR clutch solenoid  54  duty cycle is changed to feed forward control (i.e. feedback control of the DR clutch solenoid  54  is stopped) so the compounder speed is controlled to its target speed for the selected gear at a learned or predetermined rate. This provides feedback control of the final application of the 2-4 clutch  24  to ensure the turbine speed is gently brought to its target speed for the selected gear and the main box goes to the proper gear ratio without any bumps. 
         [0027]    At t 8 , the overrunning clutch  34  in the compounder  14  takes the torque capacity and the compounder speed reaches its target speed. Preferably soon thereafter, the 2 nd  gear to 3 rd  gear upshift is finished and, at t 9 , the turbine  17  reaches its target speed by way of feedback control of the 2-4 clutch as noted above and the 2-4 clutch is quickly ramped up to its line pressure. 
         [0028]    In general terms and according to the implementation discussed above, the upshift is initiated first in the main box  12 , and the speed phase in the compounder  14  begins after the speed phase in the main box  12 . This permits the positive torque in the upshift speed phase to be canceled in whole or in part by the negative torque in the downshift speed phase to enable a smooth shift. In the implementation described, the soft release of the DR clutch facilitates maintaining control of the compounder after slip starts. Then, while performing open loop control in the main box  12  for the speed phase, the compounder downshift is controlled so that the compounder output speed nears its target speed. Soon after the compounder speed is sufficiently near its target speed, the turbine speed is controlled to its target speed and the shift sequence is finished. In at least one implementation it is preferred for a smoother shift to have the compounder  14  reach its target speed just before the turbine reaches its target speed, or at the same time. 
         [0029]    While certain preferred embodiments have been shown and described, persons of ordinary skill in this art will readily recognize that the preceding description has been set forth in terms of description rather than limitation, and that various modifications and substitutions can be made without departing from the spirit and scope of the invention. For example, while the term ‘clutch’ has been used throughout the description, that term may be interchangeable with the term ‘friction element’ or other corresponding structure. Accordingly, the invention should not be limited by a particular definition of the term ‘clutch’ or by any particular construction of a ‘clutch’ used by the assignee hereof or otherwise. The invention is defined by the following claims.