Patent Publication Number: US-2013253789-A1

Title: Method For Hydraulically Filling A Clutch Without Using A Calibration Routine

Description:
FIELD OF THE DISCLOSURE  
     The present disclosure relates to a method for hydraulically filling a clutch. More specifically, the present disclosure relates to a method for hydraulically filling a clutch without using a calibration routine. 
     BACKGROUND OF THE DISCLOSURE  
     A powertrain may comprise various gears in constant mesh that are engaged in a select manner by one or more hydraulic clutches for providing a powertrain path from one shaft to another shaft, which, ultimately, results in an active speed ratio corresponding to the engaged gears. Shifting from one speed ratio to another involves releasing one or more of the clutches associated with the active speed ratio and engaging one or more clutches associated with the new, desired speed ratio. To do this, an associated proportional control valve may independently vary the flow and pressure to its respective hydraulic clutch. In some powertrains having just one proportional control valve, only one clutch can be activated at any time and, therefore, a calibration routine requiring one clutch loaded against another clutch is not possible. 
     Shift quality depends on the several factors associated with each hydraulic clutch, during the filling of the clutch, prior to engagement. Some key factors are the active speed ratio, the length of time that full flow is available to the hydraulic clutch, and the length of time that an amount less than full flow is available to the hydraulic clutch. Various off-line calibration routines have been developed to optimize these times. These routines typically employ opposing clutches or park brakes for introducing a load on the clutch being calibrated. Then, during operation, further adjustments to the calibration parameters, following the calibration routine, may be necessary as the result of temperature, viscosity, and load variations. 
     What is needed is a method for hydraulically filling the clutch that does not require a calibration routine, yet still results in high shift quality. 
     SUMMARY OF THE DISCLOSURE  
     Disclosed is a method for hydraulically filling a clutch without using a calibration routine. The clutch comprises a spring and a clutch cavity, and the spring and the clutch cavity are positioned inside of the clutch. A valve is associated with the clutch and is configured for allowing a fluid to flow to and from the clutch cavity. The method comprises the step of sending a wakeup current to a valve. The wakeup current is sent to the valve for allowing the fluid to substantially fill the clutch cavity. Still further, the method comprises the step of determining whether the spring is compressed and, also, determining whether a speed ratio of the powertrain is unknown. The method further comprises the step of sending a ramped hold current that rises relatively gradually to the valve if the spring is compressed and if the speed ratio is unknown. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description of the drawings refers to the accompanying figures in which: 
         FIG. 1 . is a simplified schematic of a clutch a control system and a powertrain; 
         FIG. 2  is flow chart of a method for hydraulically filling a clutch when a speed ratio is unknown; and 
         FIG. 3  is a graph of the method for hydraulically filling the clutch when the speed ratio is unknown. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       FIG. 1 . is a simplified schematic of a clutch control system  10  and a powertrain  7 . The clutch control system  10  comprises a controller  115 , a valve  77 , a valve  95 , a valve  125 , and a pressure source  75 . The pressure source  75  provides pressurized fluid to the valve  77  via a line  80 . The valve  77  may be connected to the controller  115  via a line  87 , the valve  95  via a line  90 , and the valve  125  via a line  85 . The valve  77  may be a proportional control valve, and may, therefore, open proportionally to the level of current that the controller  115  provides. Alternatively, the valves  95  and  125  may be on/off valves. 
     The powertrain  7  comprises an engine  5 , a transmission  25 , a forward clutch  15 , and a reverse clutch  20 . In the powertrain  7 , a gear  35  may be connected to the engine  5  via a shaft  30 . The forward clutch  15  may be coupled to gear  35 . Gear  35  may mesh with a gear  40 , the gear  40  may mesh with a gear  45 , and the gear  55  may mesh with the gear  60 . The gear  45  and the gear  55  may rotate together via a countershaft  22 . The transmission  25  may be connected to a gear  60  via the shaft  65 , and the transmission  25  may also be connected to a shaft  70 . 
     A speed sensor  145  may be adjacent to the shaft  65 , and the speed sensor  145  may be in communication with the controller  115  via a line  135 . Likewise, a speed sensor  150  may be adjacent to the shaft  70 , and the speed sensor  150  may be in communication with the controller  115  via a line  140 . A pressure gauge  105  may be in communication with a controller  115  via a line  110 , and a pressure gauge  132  may be in communication with the controller  115  via a line  137 . As discussed, the controller  115  is connected to various components. Although these connections are illustrated via physical lines, the controller  115  may also connect to some or all of the components wirelessly. 
     The valve  95  may be connected to the controller  115  via a line  127 , and it may also be connected to a forward clutch  15  via line  100 . The forward clutch  15  may comprise a housing  42 , a piston  27 , a clutch cavity  37 , one or more disks  17 , a spring  32 , and a member  62 . The piston  27  may be adjacent to a clutch cavity  37  and to the one or more disks  17 . 
     When the forward clutch  15  engages, the power flow from the engine  5  bypasses the countershaft  22 , thereby rotating the shaft  65  in a forward direction. When the forward clutch  15  disengages, the spring  32  urges the member  62  and the piston  27  away from one another, which allows the one or more disks  17  to separate from one another. Assuming that the reverse clutch  20  is also disengaged, the engine  5  no longer provides power to the transmission  25 . 
     The valve  125  may be connected to the controller  115  via a line  120 , and it may also be connected to a reverse clutch  20  via a line  130 . The reverse clutch  20  comprises a housing  44 , a piston  49 , a clutch cavity  50 , one or more disks  47 , a spring  52 , and a member  64 . The piston  49  may be adjacent to the clutch cavity  50  and to the one or more disks  47 . 
     When the reverse clutch  20  engages, the power from engine  5  flows through a countershaft  22 , thereby rotating the shaft  65  in a reverse direction. Alternatively, when the reverse clutch  20  disengages, the spring  52  may urge the member  64  and the piston  49  away from one another, which then allows the one or more disks  47  to separate from one another. As such, assuming that the forward clutch  15  is also disengaged, the engine  5  can no longer provide power to the transmission  25 . 
     Shifting the transmission  25 , from one active speed ratio to another active speed ratio, may require releasing and engaging one or more clutches (not shown) of the transmission  25 . A powertrain comprising a single clutch or one comprising multiple clutches sharing a single proportional control valve (such as the proportional control valve  77  shown in  FIG. 1 ), cannot be calibrated using traditional methods, because traditional methods require a known load for calibration. Further, when the active speed ratio is unknown, a calibrated hold value that correlates with a particular active speed ratio also cannot be used. 
       FIG. 2  shows a method for hydraulically filling a clutch when the active speed ratio is unknown, and  FIG. 3  shows a graph of the method. In  FIG. 3 , a curve  155  represents the current commanded by the controller  115  versus time, a curve  160  represents the pressure in the clutch cavity  37  versus time, and a curve  165  represents the output speed of a powertrain component versus time. It is understood that even though the method is illustrated, in  FIG. 1 , and described using the forward clutch  15 , the method could use the reverse clutch  20  or other kinds of clutches. 
     In act  210 , the wakeup mode  172  begins. In the wakeup mode  172 , the controller  115  communicates a wakeup current  141  to the valve  77 . The wakeup current  141  is shown, in  FIG. 3 , between points  180  and  185 . The wakeup current  141  may be equivalent to a current that opens the valve  77  as far possible. By sending the wakeup current  141  and, thus, opening the valve  77  as far as possible, fluid begins to rapidly fill the clutch cavity  37 . To prevent an undesirable overfill of the clutch cavity  37 , the valve  77  may transition to a slightly closed position just before the clutch cavity  37  is completely filled. Off-line calibration routines may be used for optimizing the length of time that the controller  115  continues the wakeup mode  172 . 
     Eventually, so much fluid enters the clutch cavity  37  that the spring  32  begins to compress, and in act  215 , the controller  115  and the pressure gauge  105  may be used to determine when this occurs. One way of determining when the spring  32  begins to compress is by detecting a pressure inflection point. The pressure inflection point occurs as the rate of pressure increases, in the clutch cavity  37 , suddenly decreases, even though the flow rate of fluid entering the clutch cavity  37  remains constant. The pressure inflection point signals compression of spring  32  and, also, signals that the end of the wakeup mode  172  is approaching. 
     Act  220  is to determine whether the active speed ratio is known. In a high specification transmission, sensors and switches may be employed for determining the active speed ratio. But, in a low specification transmission, the active speed ratio may only be known at certain times. For example, when operating the powertrain  7 , as shown in  FIG. 1 , shuttle shifting may used. Shuttle shifting is the reversing of a direction of motion, and this is achieved via releasing the forward clutch  15  and simultaneously engaging the reverse clutch  20  without changing the active speed ratio. In addition, shuttle shifting also refers to releasing the reverse clutch  20  and simultaneously engaging the forward clutch  15  without changing the active speed ratio. Either way, when shuttle shifting, the active speed ratio before the shuttle shift is known, so the active speed ratio after the shuttle shift is also known. 
     Act  225  may be referred to as a known hold mode (not shown), and this mode occurs if the active speed ratio is known. Conversely, the combination of acts  230 ,  235 , and  237  may be referred to as a ramped hold mode  174 , and this mode occurs if the active speed ratio is unknown. The ramped hold mode  174  is illustrated, in  FIG. 3 , between points  185  and  190 . 
     Both the known hold mode (not shown) and the ramped hold mode  174  continue filling the clutch cavity  37 , and this may begin a short time after detection of the pressure inflection point. In act  225 , when the active speed ratio is known, the controller  115  sends a known hold current (not shown) to the valve  77  that has been identified to smoothly engage the forward clutch  15 . To do this, the controller  115  may use a look-up table that correlates a given active speed ratio to an optimal known hold current (not shown). 
     If a clutch is acting upon a single active speed ratio, the known hold current (not shown) is of a constant magnitude, but if a single clutch is acting upon multiple active speed ratios, such as forward clutch  15 , a current appropriate for one active speed ratio is likely inappropriate for another. So, in act  230 , the active speed ratio is unknown, the controller  115  initially commands and ramps the hold current  142  as the current associated with the lowest active speed ratio. Then, in act  235 , the controller  115  gradually raises the ramped hold current  142  until an output speed of a powertrain component is detected. Gradually raising the ramped hold current  142  accommodates widely varying, unknown active speed ratios and promotes efficient filling of the forward clutch  15 . 
     Act  237  is to determine whether an output speed of a powertrain component is detected. The powertrain component may be, for example, the shaft  65 , the shaft  70 , or any other component of the powertrain  7  that rotates as a result of the engagement of forward clutch  15 . The speed sensor  145  or the speed sensor  150  may, for example, be used for determining whether an output speed of a powertrain component is detected. If an output speed is not detected, then the acts  235  and  237  may repeat themselves. Alternatively, if an output speed is detected, then act  240  may begin. 
     In act  240 , the modulation mode  176  begins. In the modulation mode  176 , the controller sends a modulation current  143  to the valve  77 . The modulation current  143  is shown, in  FIG. 3 , between the points  190  and  195 . In the modulation mode  176 , as the forward clutch  15  continues to engage, the controller  115  and, for example, the speed sensor  145  or the speed sensor  150  may measure the output speed of the shaft  70 . Here, the controller  115  may comprise a proportional-integral-derivative controller (not shown) for using the measured output speed as feedback and, thus, controlling the engagement of the forward clutch  15 . 
     In act  245 , a full-on mode  178  may begin, as shown in  FIG. 3 , at point  195 . In the full-on mode  178 , the controller  115  communicates a full-on current  144  to the valve  77 , which allows enough fluid to enter clutch cavity  37  to fully engage the forward clutch  15 . 
     While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. It will be noted that alternative embodiments of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the present invention as defined by the appended claims.