Abstract:
The present invention provides an apparatus and method for estimating the realtime position of a clutch piston during the fill cycle using noisy pressure measurements which ensures proper and desired clutch operation. Pressures on both sides of a flow controlling orifice, at the fluid control actuator and the clutch cylinder are measured and these measurements in conjunction with other system parameters such as orifice size, clutch volume and return spring characteristics are used to solve nonlinear dynamic equations (algorithms) which reside in a microprocessor. The microprocessor provides outputs corresponding to an estimate of the current position of the clutch piston, an estimate of the current speed of the piston and an estimate of the current hydraulic pressure. The method can also be utilized to detect clutch wear.

Description:
FIELD 
       [0001]    The present disclosure relates to estimating in realtime a position of a clutch component and more particularly to estimating in realtime the position of a piston of a hydraulically operated clutch. 
       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]    There are numerous ways to classify or categorize automatic transmissions for motor vehicles. Perhaps the most popular and practical way relates to the overall speed ratio change structure. Given this criterion, planetary gear, continuously variable and dual clutch transmissions constitute the three currently most popular types. 
         [0004]    Another way to classify automatic transmissions relates to their speed ratio shift configuration. Certain transmissions are classified as clutch-to-clutch transmissions meaning that each shift is accomplished by the release or disengagement of at least one clutch and the activation or engagement of at least one other clutch. This class of automatic transmissions includes most multiple planetary gear and all dual clutch transmissions. 
         [0005]    In clutch-to-clutch transmissions, the manner of clutch engagement and disengagement, that is, how quickly engagement (or disengagement) begins after a command, the rate of engagement dE/dt (or disengagement dD/dt), and the time to full engagement (or disengagement), for example, are critical to the overall satisfactory transmission operation and performance which demands consistent and smooth shifts. 
         [0006]    In clutch-to-clutch transmissions, to engage a clutch controllably, the piston actuating the clutch is moved to a point at which the full stroke of the clutch is completed. Thus, the clutch volume is completely filled with transmission or hydraulic fluid. After this “fill phase,” the torque transmitted by the clutch is then controlled by controlling the clutch fluid pressure. 
         [0007]    Prior art clutch control systems rely on collecting indirect information and utilizing it after a shift has been completed to determine the required fill time and time to begin full clutch engagement. This approach is limited by the numerous calibrations that must be utilized to relate the available data to the fill volume and the slow convergence rate of this limited data which delays and adds uncertainty to the computation of the clutch fill time. 
         [0008]    As the sophistication of clutch-to-clutch and other transmissions increases and their performance and fuel efficiency goals become even more demanding, controlled, that is, proper and desired engagement and disengagement of clutches in clutch-to-clutch and other transmissions is of increasing importance. The present invention is directed to this goal. 
       SUMMARY 
       [0009]    The present invention provides an apparatus and method for estimating the realtime position of a clutch during the fill cycle using noisy pressure measurements to ensure proper and desired clutch operation. Pressures on both sides of a flow controlling orifice, at the fluid control actuator and the clutch cylinder are measured and these measurements in conjunction with other system parameters such as orifice size, clutch volume and return spring characteristics are used to solve nonlinear dynamic equations (algorithms) which reside in a microprocessor. The microprocessor provides outputs corresponding to an estimate of the current position of the clutch piston, an estimate of the current speed of the piston and an estimate of the current hydraulic pressure. The method can also be utilized to detect clutch wear. 
         [0010]    Thus it is an aspect of the present invention to provide an apparatus for estimating the realtime position of a clutch piston during its fill cycle. 
         [0011]    It is a further aspect of the present invention to provide a method for estimating the realtime position of a clutch piston during its fill cycle. 
         [0012]    It is a still further aspect of the present invention to provide an apparatus for estimating the realtime position of a clutch during the fill cycle using noisy pressure measurements. 
         [0013]    It is a still further aspect of the present invention to provide a method for estimating the realtime position of a clutch during the fill cycle using noisy pressure measurements. 
         [0014]    It is a still further aspect of the present invention to provide an apparatus for providing a realtime estimate of the current position of the clutch piston, the current speed of the piston and the current hydraulic pressure. 
         [0015]    It is a still further aspect of the present invention to provide a method for providing a realtime estimate of the current position of the clutch piston, the current speed of the piston and the current hydraulic pressure. 
         [0016]    Further aspects, 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 
         [0017]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0018]      FIG. 1  is a schematic view of a portion of a motor vehicle transmission incorporating the present invention; 
           [0019]      FIG. 2  is a block diagram of a microprocessor embodying the algorithms of the present invention; 
           [0020]      FIG. 3  is a graph presenting measured and estimated clutch pressure with clutch pressure on the vertical (Y) axis and time on the horizontal (X) axis; and 
           [0021]      FIG. 4  is a graph presenting estimated and true clutch displacement with clutch piston displacement on the vertical (Y) axis and time on the horizontal (X) axis. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0023]    With reference to  FIG. 1 , a portion of an automatic transmission such as a dual clutch transmission is illustrated and generally designated by the reference number  10 . The transmission  10  includes a housing  12  having various openings, flanges and other features which receive, locate and support the internal components of the transmission  10 . Among those components are an input shaft  14  which is coupled to and drives an input clutch assembly  16  having a friction clutch pack  18  or similar selectively engageable, torque transmitting device. A drive shaft or output member  22  couples and delivers the torque from the friction clutch pack  18  to other components within the transmission  10 . 
         [0024]    The clutch assembly  16  also includes a typically annular cylinder  24  which receives an axially slidable piston  26  which engages and compresses the friction clutch pack  18 . Preferably, a wave plate  28  which provides variable stiffness properties to the friction clutch pack  18  resides between the piston  26  and the friction clutch pack  18 . Alternatively, the wave plate  28  may be disposed adjacent the face of the friction clutch pack opposite the piston  26 . A return spring  32  provides a restoring or return force to the piston  26  to translate it away from the friction clutch pack  18  when hydraulic pressure within the cylinder  24  is reduced in accordance with conventional design practice. 
         [0025]    The transmission  10  also includes a hydraulic fluid (transmission oil) supply and control system  40 . The supply and control system  40  includes a hydraulic pump  42  and line pressure control system. The hydraulic pump  42  may be driven directly by an electric motor or driven directly or indirectly from the input shaft  14  of the transmission  10  or the output shaft of a prime mover (not illustrated). The output of the hydraulic pump  42  is provided to a hydraulic supply line  44  which is in fluid communication with an optional accumulator  46 . As is well known, the accumulator  46  is a storage device for pressurized hydraulic fluid that stabilizes system pressure and fluid delivery when, for various reasons, fluid consumption exceeds fluid supply. In certain systems and for various reasons, the accumulator  46  may be omitted without sacrificing or compromising proper system operation. Through the supply line  44 , hydraulic fluid is provided to a proportional solenoid actuator or control valve  50  such as a variable bleed solenoid valve (VBS) along with a pressure regulating valve, a variable feed solenoid valve (VFS) or other proportioning valve which is controlled by a variable signal such as an analog voltage, or pulse width modulated (PWM) signal from a transmission control module (TCM) or similar controller  52 . 
         [0026]    The proportional actuator or control valve  50  provides a controlled flow of hydraulic fluid in a supply line  54  to a first actuator pressure sensor  56 . The first actuator pressure sensor  56  provides a continuously variable, i.e., proportional or analog, electrical signal or output in a lead or cable  58  to the controller  52 . The supply line  54  also communicates with a flow restricting orifice  60 . Depending upon instantaneous operating conditions, the orifice  60  limits hydraulic fluid flow and creates a pressure differential, as will be more fully described subsequently. The size of the orifice  60  depends upon many operating parameters such as the pressure and flow characteristics of the hydraulic pump  42  and the accumulator  46  and the pressure, flow and force characteristics of the clutch assembly  16  and may be experimentally or empirically determined. It should be appreciated that hydraulic fluid pressure in the supply line  54  ahead of the orifice  60  may also be read by another or pre-existing sensor (not illustrated) that is a component of the transmission  10  itself or another transmission sub-system. In other words, the first actuator pressure sensor  56  need not be a sensor dedicated to this system but may be a component of another system or sub-system of the transmission  10 . 
         [0027]    The orifice  60  provides hydraulic fluid to a clutch supply line  62  which communicates with both the cylinder  24  of the clutch assembly  16  and a second clutch pressure sensor  66 . The second clutch pressure sensor  66  is preferably located as close as is practical to the clutch cylinder  24  in order to most accurately sense the pressure therein. The second clutch pressure sensor  66  is preferably a device identical to the first pressure sensor  56  and also provides a continuously variable, i.e., proportional or analog, electrical signal or output in a lead or cable  68  to the controller  52 . 
         [0028]    It will be appreciated that in operation, the transmission control module  52  receives or generates commands that proportionally open or close the actuator or control valve  50 . The first actuator pressure sensor  56  senses hydraulic pressure proximate the outlet of the actuator or control valve  50 , before the orifice  60  and the second clutch pressure sensor  66  senses hydraulic pressure after the orifice  60 , closer to the clutch cylinder  24 . This information is provided in the leads or cables  58  and  68  to the transmission control module  52 . and is utilized as described below to generate a realtime estimate of the position of the hydraulic piston  26  as it translates within the cylinder  24  and applies force to the friction clutch pack  18 . 
         [0029]    Referring now to  FIG. 2 , a block diagram of the model based observer including the computational software or algorithms which may reside in the transmission control module  52  or a similar device is illustrated and generally designated by the reference number  70 . The model based observer  70  receives signals or data from the first sensor  56  in the lead or cable  58  and from the second sensor  66  in the lead or cable  68  which is provided to a model-based prediction processor  72  which contains algorithms which will be described subsequently. The output of the model-based prediction processor  72  is provided to a measurement correction processor  74 . The measurement correction processor  74  also contains algorithms which will be described subsequently and provides three data or signal outputs. A first output  76  is or represents an estimate of the present position of the hydraulic piston  26  and thus the extent of engagement of the friction clutch pack  18 ; the second output  78  is or represents an estimate of the present axial speed of the piston  26  and thus, for example, how soon and how abruptly engagement of the friction clutch pack  18  will occur; and a third output  82  is or represents an estimate of the present pressures at the output of the actuator or control valve  50  and at the input to the hydraulic cylinder  24 . 
         [0030]    Returning to the model-based prediction processor  72 , it includes a force-motion (F=ma) equation which computes the acceleration of the hydraulic piston  26  based upon several system variables and the pressure sensed at the cylinder  24  by the second pressure sensor  66 : 
         [0000]        {umlaut over (x)}   p   ={A   p   P   p   −D   p   {dot over (x)}   p   −F   drag ( P   p )tan  h ( {umlaut over (x)}   p /α)− k   p ( x   p   +x   po )− F   apl   }/M   p  
 
         [0031]    The instantaneous rate of change in the pressure at the hydraulic cylinder  24  per unit time may then be computed with the following equation: 
         [0000]    
       
         
           
             
               
                 p 
                 . 
               
               p 
             
             = 
             
               
                 β 
                 
                   ( 
                   
                     
                       V 
                       o 
                     
                     + 
                     
                       
                         x 
                         p 
                       
                        
                       
                         A 
                         p 
                       
                     
                   
                   ) 
                 
               
                
               
                 { 
                 
                   
                     
                       sign 
                        
                       
                         ( 
                         
                           
                             p 
                             out 
                           
                           - 
                           
                             p 
                             p 
                           
                         
                         ) 
                       
                     
                      
                     
                       C 
                       d 
                     
                      
                     
                       m 
                       clfd 
                       2 
                     
                      
                     
                       
                         
                           2 
                           p 
                         
                          
                         
                            
                           
                             
                               p 
                               out 
                             
                             - 
                             
                               p 
                               p 
                             
                           
                            
                         
                       
                     
                   
                   - 
                   
                     
                       
                         x 
                         . 
                       
                       p 
                     
                      
                     
                       A 
                       p 
                     
                   
                 
                 } 
               
             
           
         
       
     
         [0032]    This yields 
         [0000]        {dot over (X)}=f ( X,p   out   ,C ) 
         [0000]    where 
         [0000]    
       
         
           
             X 
             = 
             
               ( 
               
                 
                   
                     
                       x 
                       p 
                     
                   
                 
                 
                   
                     
                       
                         x 
                         . 
                       
                       p 
                     
                   
                 
                 
                   
                     
                       p 
                       p 
                     
                   
                 
               
               ) 
             
           
         
       
     
         [0000]    X represents a vector quantity of the system state variables that include, but are not limited to, position of the piston  26 , speed of the piston  26  and pressure at the cylinder  24  and C is equal to a set of parameters. 
         [0033]    These computations occurring in the model-based prediction processor  72  are summed with a computation occurring in the measurement correction processor  74  in the following step: 
         [0000]        {tilde over ({dot over (X)}=f ( {tilde over (X)},p   out-m   ,C )+ g ( p   p     m     −{tilde over (p)}   p ) 
         [0000]    which can be integrated to provide {tilde over (X)} which is the estimated value of X, the desired variable, namely the present position of the piston  26 , {tilde over (p)} which is the estimated value of p which is the pressure at the hydraulic cylinder  24 , Ppm is the hydraulic pressure measured value from the second sensor  66  at the clutch cylinder  24  and Pout-m is the hydraulic pressure measured value for the first sensor  56  at the output of the actuator or control valve  50 . A listing of all the variables which appear in the foregoing equations appears on page  12  of this specification. 
         [0034]    Thus by using the measured pressures Ppm and Pout-m, one can estimate the other state variables. It will be appreciated that the choice of the functions ƒ({tilde over (X)}, Pout-m, C) and g(Ppm−{tilde over (P)}p) shall be different for different techniques like Kalman filter and sliding mode observer methodologies. For example, g(Ppm−{tilde over (P)}p) can be a gain that may be computed using a Kalman filter methodology while a gain multiplied by a signum function may be computed using a sliding mode methodology. The rationale behind adding a function of the error g(Ppm−{tilde over (P)}p) is to provide a computational feedback mechanism to correct the overall estimate based on the available clutch pressure measurement Ppm and its estimate Pp. It must be appreciated hence that other estimation methods may be utilized to calculate the states relevant for this application. 
         [0035]    With reference now to  FIGS. 3 and 4 , it should be understood that one of the primary benefits of the Kalman Filter, its progeny, and their data analysis and computational techniques is the reduction of the effect of noise in a signal. As utilized herein, noise refers to any variation in a signal that can be and is assumed to be a divergence from the actual, true and present value of a measured variable. As  FIG. 3  illustrates, the measurement and data analysis techniques of the present invention minimize the effects of noise in the control loop. The plot or line  82  illustrates the raw (unfiltered and unconditioned) data supplied by one of the sensors  56  or  66 . It can de appreciated that interpretation of such a data stream may be difficult and that control and transmission operating decisions based upon an instantaneous value may not be optimal. The plot or line  84  represents the pressure value estimated by the above-noted algorithms and utilized to estimate the position of the piston  26 .  FIG. 4  presents two plots of piston displacement versus time, showing the close agreement between the position of the piston  26  estimated by the above-noted algorithms ( 86 ) and the position of the piston  26  confirmed by a truth model ( 88 ). 
         [0036]    It should be understood that the foregoing description sets forth the best mode contemplated by the inventors for practicing the invention, especially with regard to the incorporation and use of the two pressure sensors  56  and  66  on opposite sides of the orifice  60 . However, it should be understood that two alternatives exist which achieve the purpose and goal of the invention but which do not expressly require the first pressure sensor  56 . In a first alternative, the first (dedicated) pressure sensor  56  can be replaced with a sensor that is a component of another control or monitoring system (not illustrated). The output of this other, typically pre-existing sensor may then also be provided to and utilized by the controller  52 . This, of course, eliminates what might be considered a redundant pressure sensor, thereby saving weight and reducing cost. In a second alternative, the pressure in the supply line  54  is assumed to be the desired (design) system operating pressure such 1000 kPa. Such system design pressures can vary between about 200 kPa and 2200 kPa. Although this assumption has been found to lead to some error in the computation of the piston position estimate and other data, it does provide a viable and operable computational scheme, again without the necessity of incorporating the first pressure sensor  56 . 
         [0037]    Last of all, since the foregoing apparatus and method provides a realtime estimate of the position of a piston in a friction clutch assembly of a vehicular transmission based on sensed hydraulic pressures in the clutch circuit, it is also possible and should be understood to have utility as well to sense clutch wear, that is, a wearing away of the friction material of the friction clutch pack  18  such that increased piston displacement is necessary to achieve the same level of clutch engagement and torque transfer as in the past. 
         [0038]    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. 
       LISTING OF SYMBOLS UTILIZED IN EQUATIONS 
       [0039]    
       
         
           
             
               ( 
               
                 
                   
                     
                       x 
                       p 
                     
                   
                 
                 
                   
                     
                       
                         x 
                         . 
                       
                       p 
                     
                   
                 
                 
                   
                     
                       p 
                       p 
                     
                   
                 
               
               ) 
             
             = 
             
               ( 
               
                 
                   
                     
                       Piston 
                        
                       
                           
                       
                        
                       Displacement 
                     
                   
                 
                 
                   
                     
                       Piston 
                        
                       
                           
                       
                        
                       Velocity 
                     
                   
                 
                 
                   
                     
                       Pressure 
                        
                       
                           
                       
                        
                       at 
                        
                       
                           
                       
                        
                       Clutch 
                        
                       
                           
                       
                        
                       Chamber 
                     
                   
                 
               
               ) 
             
           
         
       
       
         A p =Piston Area 
         D p =Viscous Drag Coefficient at Piston 
         F drag =Friction Drag on Piston 
         α=Friction Drag Parameter 
         k p =Spring Constant of Return Spring at Piston 
         x po =Initial Piston Position 
         F apl =Force due to Wave Plate at the Clutch 
         M p =Mass of the Piston 
         β=Bulk Modulus of Transmission Fluid 
         V o =Initial Clutch Chamer Volume 
         P out =Pressure before the orifice between control solenoid valve and clutch 
         C d =Flow Discharge Coefficient the orifice between control solenoid valve and clutch 
         r clfd =Effective Flow Radius of orifice between control solenoid valve and clutch 
         p=Mass Density of Transmission Fluid 
         h 1 =Piston displacement when wave plate compression starts 
         h 1 =Piston displacement when wave plate compression starts 
         C=set of all parameters listed above that is used to model the clutch