Abstract:
A method of detecting substantial filling of a hydraulic cylinder of a hydraulically operated clutch of a vehicular transmission is disclosed and claimed. A pressure sensor disposed in a hydraulic line to the clutch cylinder provides a signal that the hydraulic pressure has dropped as the clutch cylinder begins to fill and also that the pressure has returned to a substantially normal level. The pressure sensor may be a continuously variable output such as an analog sensor, pulse width modulation (PWM) sensor, a similar device or, less desirably, a two state sensor. An iterative algorithm utilizes data from the sensor and a timer to determine when clutch fill is substantially complete.

Description:
FIELD 
       [0001]    The present disclosure relates to an operating method for a hydraulic clutch and more particularly a method of detecting completion of filling of a hydraulic clutch in a vehicle transmission. 
       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 many automatic transmissions, hydraulic piston and cylinder assemblies engage and disengage clutches to achieve a desired power flow path corresponding to a desired gear ratio or speed, typically in a sequence of gear ratios or speeds. Such operation occurs in both clutch-to-clutch (multiple planetary) and dual clutch (DCT) transmissions. 
         [0004]    In such transmissions, the smoothness and overall quality of a shift is primarily determined by the characteristics of clutch engagement, for example, how quickly clutch engagement begins after a clutch engagement command and how rapidly the clutch engages. Such clutch engagement characteristics are, in turn, the product of hydraulic fluid application, that is, the pressure of fluid application, the volume of fluid application and the duration and time based function of these application characteristics. 
         [0005]    In these transmissions, it is often desirable to know the status of hydraulic clutches, especially as filling nears completion when the hydraulic pressure on the clutch can be controlled to achieve controlled and optimum clutch engagement. 
         [0006]    In such transmissions, if clutch pressure control is begun when the hydraulic chamber of the clutch is not fully filled with transmission oil, it may result in engine flare when the engine speed rises suddenly due to lack of load. Similarly, when the clutch fill phase is extended for longer than necessary, sudden, uncontrolled engagement of the clutch may result and cause a bumpy gear shift or a transmission tie-up. Hence, it is important to monitor clutch fill pressure and fill the clutch chamber exactly as appropriate and than continue to the next phase to maintain shift quality and increase reliability on clutch materials. 
         [0007]    The present invention is directed to a method of detecting substantial filling of a hydraulic cylinder of a hydraulically operated clutch of a vehicular automatic transmission. 
       SUMMARY 
       [0008]    The present invention provides a method of detecting substantial filling of a hydraulic cylinder and incipient full engagement of a hydraulically operated clutch of a vehicular automatic transmission. Because hydraulic pumps in automatic transmissions are sized to provide and satisfy an average or nominal flow, when certain large flow events occur, such as filling of a clutch cylinder, hydraulic pump pressure may drop temporarily and rebound as the clutch cylinder fills and the clutch nears its travel limit. In hydraulic systems where this occurs, the pressure/time relationship in a supply line may be measured and utilized to anticipate clutch filling and thus pressure control and full engagement of the clutch can be carried out. 
         [0009]    A pressure sensor disposed in the main hydraulic line or in a location that is being fed by the main line such as another fully applied (on) holding clutch in the transmission of the control system provides a signal, first that the main line or supply hydraulic pressure from the pump has dropped as the clutch cylinder begins to fill and second, that the pressure has returned to a substantially normal level. The pressure sensor may be a continuously variable output such as an analog sensor, pulse width modulation (PWM) sensor, simple switch or similar device. An iterative algorithm utilizes data from the sensor and a timer to determine when clutch fill is substantially complete. Depending upon pump delivery flow rates and pressures, clutch cylinder size and operating pressure, flow rates and restrictions between the pump and the cylinder and proper selection of predetermined values in the algorithm, the method provides an indication that the clutch cylinder is substantially full of oil and that the pressure control can be carried out at the clutch 
         [0010]    Thus it is an object of the present invention to provide a method of determining the incipient end of fill phase of a hydraulic clutch. 
         [0011]    It is a further object of the present invention to utilize a pressure sensor in a hydraulic line in the control system to determine the incipient end of fill phase of the clutch. 
         [0012]    It is a still further object of the present invention to provide a method of sensing hydraulic pressure supplied to a hydraulic clutch cylinder to indicate incipient end of fill phase of the clutch. 
         [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 view of a portion of a transmission having a hydraulically operated clutch and pressure sensor according to the present invention; 
           [0016]      FIG. 2  is a graph of hydraulic clutch line pressure and clutch engagement versus time of a typical hydraulically operated clutch; 
           [0017]      FIG. 3  is a flow chart of the method of determining hydraulic clutch fill according to the present invention; 
           [0018]      FIG. 4  is a schematic view of a portion of a transmission having an accumulator, a hydraulically operated clutch and pressure sensor according to the present invention; and 
           [0019]      FIG. 5  is a graph of hydraulic clutch line pressure and clutch engagement versus time of a typical hydraulically operated clutch being fed by an accumulator. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0021]    With reference to  FIG. 1 , a portion of an automatic transmission incorporating the present invention is illustrated and generally designated by the reference number  10 . The automatic transmission  10  includes a rotatable input shaft  14  which provides drive torque to a clutch assembly  16  from a prime mover (not illustrated) such as a gas, Diesel, flex fuel, hybrid or electric power plant. It should be understood that the clutch assembly  16  is representative only and that, typically, multiple clutches will be utilized in a transmission and that the clutch locations may be at the input to the transmission, within the transmission or both. The clutch assembly  16  includes a hydraulic cylinder  18  which receives a bi-directionally slidable hydraulic apply piston  22 . The hydraulic apply piston  22  acts upon and compresses or releases an associated friction clutch pack  24  which selectively transfers drive torque from the input shaft  14  to a drive shaft or output member  26  and, in turn, to components within the transmission  10 . The clutch pack  24  may also contain wave plates (not illustrated) that provide variable stiffness properties to the clutch pack  24  along with the clutch plates. Typically, the clutch assembly  16  will also include a return spring  28  which acts upon the apply piston  22  to assist release of the friction clutch pack  24  when hydraulic pressure to the hydraulic cylinder is removed or lowered. 
         [0022]    The transmission  10  includes a hydraulic pump  30  that may be driven directly (or indirectly through a geared connection) from the input shaft  14 , the output shaft of the prime mover or may be driven independently by a dedicated electric motor (not illustrated). The hydraulic pump  30  provides pressurized hydraulic fluid (transmission oil) to an outlet or supply line  32  that communicates with a line pressure control system  34  (LPCS) which may include various electromechanical devices such as solenoid control valves and pressure regulators. In fluid communication with the output of the line pressure control system  34  is a fluid supply line  36  which is connected to a line pressure sensor  40  having an output which corresponds to the instantaneous hydraulic fluid pressure in the fluid supply line  36 . It should be apparent that the sensor  40  may also be disposed in other locations such as a fully applied clutch as long as it is capable of monitoring or measuring variations in the main supply pressure. The fluid pressure sensor  40  is preferably a proportional device having, for example, a continuously or intermittently variable output such as an analog, pulse width modulation (PWM) or similar output which is supplied to, for example, a transmission control module (TCM)  42  or similar device. Electronic conditioning, scaling and temperature compensating circuitry, if desired, may be included within the transmission control module  42 . Alternatively, the output of the fluid pressure sensor  40  may be provided directly to a clutch pressure control system (CPCS)  44 . 
         [0023]    From the fluid pressure sensor  40 , the fluid supply line  36  is connected to and supplies hydraulic fluid to a clutch pressure control system  44 . The clutch pressure control system  44  preferably includes, for example, one or more proportioning or variable bleed (VBS) solenoid valves along with pressure regulator valves or variable force solenoid valves (VFS) or similar devices shown as  46  which allows control of the flow and pressure of hydraulic fluid provided to a hydraulic line  48  which communicates with the hydraulic cylinder  18  of the clutch assembly  16 . The clutch pressure control system  44  may also include a microprocessor and related electronic components. Typically, the clutch pressure control system  44  will operate in conjunction with and receive data and commands from the transmission control module (TCM)  42 . 
         [0024]    Referring now to  FIGS. 1 and 2 , a diagram showing the performance of a typical hydraulic supply system of a transmission, such as the transmission  10  during a clutch fill cycle and engagement cycle, is presented. The horizontal (X) axis represents time and the vertical (Y) axis represents different hydraulic fluid pressures in the system. The upper, irregular horizontal line  50  represents and indicates the instantaneous hydraulic pressure in the fluid supply line  36  as sensed by the fluid pressure sensor  40 . Moving to the right across the diagram, the vertical event line  52  represents the desired pressure command to the clutch pressure control system  44  from the transmission control module (TCM)  42  or similar device to engage the clutch assembly  16  by filling the cylinder  18  and translating the piston  22 . The upwardly moving, irregular line  54  represents the actual pressure within the clutch cylinder  18 . 
         [0025]    After the start of the desired clutch pressure command  52 , there is a lot of flow demand at the clutch assembly  16  when the fluid from the line pressure system  36  flows into the clutch cylinder  18  through the hydraulic line  48  to begin stroking the clutch piston  22 . During this time, the actual pressure at the clutch cylinder  18  follows a low pressure value that depends on the stiffness of the return spring  28  and the apply area of the piston  22 . When the clutch piston  22  nears the end of its stroke, it is in full contact with the clutch pack  24  and the gap between the plates of the friction pack  24  is reduced to a minimum. At this point, the flow demand reduces as the clutch assembly  16  has completed stroking the piston  22  and the clutch fill phase is completed. Then, with the command pressure  52  being the same, the pressure at the clutch  54  begins to rise quickly as controlled by the control system  44  and finally settles down around the value of  52 . 
         [0026]    During the clutch fill process, the relationship between the lines  50  and  54  should be noted. During the clutch fill phase, the pump  30  which is usually flow limited, will be unable to maintain the same line pressure and the high flow requirement at the same time. As a result, there is a temporary drop in system line pressure  50  during the clutch fill phase. As this initial volume flow into the clutch cylinder  18  subsides at the end of the clutch fill phase and the pressure begins to build toward full clutch engagement pressure, the line pressure sensed by the pressure sensor  40  begins to return to a nominal, operating pressure. This return to the nominal operating pressure precedes full pressure in the clutch cylinder  18  and full engagement of the friction clutch pack  24  of the clutch assembly  16 . 
         [0027]    Referring now to  FIGS. 1 and 3 , an algorithm which can be embodied in the software of a microprocessor of the transmission control module  42  or the clutch pressure control system  44  is illustrated and designated by the reference number  60 . The software algorithm  60  begins with a start or initializing step  62  which is commenced upon a clutch fill command or instruction from the transmission control module  42  or similar device. The start or initializing step  62  will typically undertake such sub-steps as clearing arithmetic registers and resetting counters to zero or other desired initial values. The software  60  then moves to a process step  64  which measures the line pressure (L) from the pressure sensor  40  and the current time value (T) from an elapsed time counter which was reset to zero in the initializing step  62 . With this current data measured and stored in temporary registers, the algorithm  60  moves to a decision point  66  which undertakes a calculation and a two step interrogation. First of all, the decision point  66  computes the derivative dL/dT from the data measured and stored in the preceding step and determines whether it is less than a first predetermined or preset threshold rate of change. The derivative dL/dT can be calculated by one of many possible methods. The predetermined rate of change will depend upon the flow rate and pressure characteristics of the hydraulic pump  30 , the volume and nominal fill rate of the hydraulic cylinder  18  of the clutch assembly  16  and transmission and clutch operational characteristics and performance considerations. It may be selected empirically, arrived at experimentally or determined through other means and methods. 
         [0028]    The decision point  66  also interrogates the count timer and determines whether the current time T has exceeded or is greater than a second predetermined or preset threshold time. Once again, the predetermined or preset threshold time value will depend both upon the hydraulic and mechanical operating characteristics of the pump  30  and the clutch assembly  16  as well as the operational and desired performance characteristics of the transmission  10 . These interrogations are combined using an AND operation and if one or both are not true, the decision point  66  is exited at NO and the algorithm  60  loops back to the process step  64  where new values of the line pressure L and the timer count T are measured and stored. 
         [0029]    If both conditions are satisfied, i.e., the rate of change of dL/dT is less than the predetermined rate and T is greater than the predetermined threshold time, the decision point  66  is exited at YES and a process step  68  is entered which provides a signal or indication or achieves a state indicating to associated circuitry or devices that the end of clutch fill has been detected. The algorithm  60  then concludes at an end step  70 . Associated with this end step  70  is a diagnostic decision point  72  which inquires whether dL/dT is greater that the first predetermined or preset rate utilized above during the torque phase of operation of the transmission  10 , where the torque phase is the subsequent phase of clutch engagement after the clutch fill phase in a typical upshift. If it is, the diagnostic decision point  72  is exited at YES which sets a flag indicating a clutch underfill. If it is not, the diagnostic decision point  72  is exited at NO and no action is taken. 
         [0030]    An alternate for monitoring the threshold rate could also be understanding and characterizing the drop in pressure expected during a fill phase. In this case, the entrance and exit of fill can be simply characterized by a threshold pressure or a characteristic drop in pressure. 
         [0031]    Referring now to  FIG. 4 , it should be apparent to those skilled in the art that the pump and the line pressure regulator can be replaced by an accumulator fed by a hydraulic source and that very similar strategies of determining the end of fill can be employed.  FIG. 4  is essentially the same as  FIG. 1 , wherein the portion of the transmission  10  includes the shafts  14  and  26 , the clutch assembly  16 , the pump  30  and all the other components therein illustrated, the above descriptions being incorporated herein by reference. Additionally, an accumulator  31  is disposed in fluid communication with the outlet or supply line  32 . The accumulator  31  stores and provides a volume of hydraulic fluid under system pressure. During a fill phase, the accumulator  31  will show distinctly different rate of discharge during a clutch fill compared to the natural leakage of the system. Using similar methodologies and sensors, these changes in rates can be observed with a line pressure sensor  40  and the end of fill can be learned. 
         [0032]    Referring now to  FIG. 5 , which is similar to  FIG. 2  but relates to operation of the system with the accumulator  31  illustrated in  FIG. 4 . Once again, the horizontal (X) axis represents time and the vertical (Y) axis represents different hydraulic fluid pressures in the system. The upper, irregular line  56  represents and indicates the instantaneous hydraulic pressure in the fluid supply line  32  at the inlet/outlet of the accumulator  31 . The vertical event line  52  represents the clutch command to the clutch pressure control system  44  from the transmission control module (TCM)  42  or similar device to engage the clutch assembly  16  by filling the cylinder  18  and translating the piston  22 . The upwardly moving, irregular line  54  represents the actual pressure within the clutch cylinder  18 . It will be appreciated that as the clutch cylinder  18  is filling, the pressure at the accumulator  31  is dropping and at the end of clutch fill, the pressure within the cylinder  18  begins to build while the pressure at the accumulator  31  stabilizes. 
         [0033]    It will thus be appreciated that the present invention provides a method of detecting and providing a signal or indication to, for example, a transmission control module or other componentry associated with a vehicular automatic transmission or the powertain, that a hydraulic fluid clutch is substantially or essentially fully filled and that friction coupling and torque throughput is approaching its full operational value. This information is highly useful for the control systems of such transmissions, facilitating achievement of rapid, smooth and energy efficient gear shifts. 
         [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.