Abstract:
A method for determining when in the course of a shift event an on-coming clutch gains torque capacity is provided. The method includes closed-loop controlling an off-going clutch to maintain a predetermined slip threshold by generating an off-going clutch pressure command, causing the on-coming clutch to engage during the closed loop control of the off-going clutch, generating a first derivative with respect to time of the off-going clutch pressure command, and using the first derivative to determine when the on-coming clutch gained torque capacity. A neural network method is preferably employed in analyzing the first derivative to locate a transition in the rate of commanded pressure indicative of off-going clutch release. A corresponding apparatus is also provided.

Description:
TECHNICAL FIELD 
     This invention relates to automatic vehicle transmissions that are characterized by closed-loop control of an off-going clutch pressure command to maintain a predetermined slip threshold, and that exploit data from the first and second derivatives of the off-going clutch pressure command to determine when an on-coming clutch gains torque capacity. 
     BACKGROUND OF THE INVENTION 
     In general, a motor vehicle automatic transmission includes a number of gear elements and selectively engageable friction elements (referred to herein as clutches) that are controlled to establish one of several forward speed ratios between the transmission input and output shafts. The input shaft is typically coupled to the vehicle engine through a fluid coupling such as a torque converter, and the output shaft is coupled to the vehicle drive wheels through a differential gear set. 
     Shifting from a currently established speed ratio to a new speed ratio involves, in most cases, disengaging a clutch (off-going clutch) associated with the current speed ratio and engaging a clutch (on-coming clutch) associated with the new speed ratio. Each such shift includes a fill or preparation phase during which an apply chamber of the on-coming clutch is filled in preparation for torque transmission. Once filled, the on-coming clutch transmits torque in relation to the clutch pressure, and the shift can be completed using various control strategies. 
     In a clutch-to-clutch transmission, disengagement of the off-going clutch and engagement of the on-coming clutch is accomplished by a transmission controller transmitting pressure commands to alter the pressure and fluid volume in the respective apply chambers. The transmission controller must take into account such variables as the volume of fluid necessary to fill each clutch&#39;s respective apply chamber, fluid flow rates, fluid temperature, etc., in generating the pressure commands to ensure proper timing of the clutches. If an on-coming clutch gains torque capacity prior to disengagement of the off-going clutch, then transmission tie-up may occur. If an on-coming clutch gains torque capacity too long after the off-going clutch disengages, then engine flare will occur. 
     The prior art includes clutch-to-clutch transmissions that employ closed loop control of the off-going clutch during a shift event such that the off-going clutch maintains a predetermined slip threshold. As the on-coming clutch gains torque capacity, the speed of the input shaft drops. The transmission controller, as a result of the closed loop control of the off-going clutch, will compensate by reducing the pressure command for the off-going clutch as the on-coming clutch gains capacity until the off-going clutch torque capacity is zero. 
     SUMMARY OF THE INVENTION 
     A method and apparatus for use with an automatic transmission having an off-going clutch and an on-coming clutch during a speed ratio shift event is provided. The method enables accurate determination during vehicle operation of when, in the course of a shift event, an on-coming clutch gains torque capacity. The method includes controlling the off-going clutch using closed loop control to maintain a predetermined slip threshold. Controlling the off-going clutch includes generating an off-going clutch pressure command to which the off-going clutch is responsive and that varies with respect to time. The method also includes causing the on-coming clutch to gain torque capacity while controlling the off-going clutch, determining the first derivative with respect to time of the off-going clutch pressure command, and determining when the on-coming clutch gained torque capacity using the first derivative. 
     In the preferred embodiment, a k-means neural network algorithm is employed in determining when the on-coming clutch gains torque capacity. More specifically, the method preferably includes generating a set of data points corresponding to local minima and local maxima of the first derivative. Each of the data points includes a time value and a first derivative value (i.e., the rate of change of the commanded pressure in the off-going clutch apply chamber) for one of the local minima or maxima. The method also preferably includes using a k-means algorithm to classify each of the data points into one of a first group and a second group, the data points in the second group having later time values than the data points in the first group, and determining the data point having the earliest time value in the second group. 
     The ability to determine, during vehicle operation, when in the course of a shift event the on-coming clutch gains torque capacity enables a transmission controller to determine the accuracy of the variables and calculations employed in generating pressure commands and to make appropriate adjustments as necessary to optimize the timing of the on-coming clutch. 
     A corresponding apparatus is also provided. 
     The above objects, features and advantages, and other objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an automatic transmission; 
         FIG. 2  is a truth table indicating a relationship between transmission clutch activation and corresponding speed ratio; 
         FIG. 3  is a graphical depiction of an off-going clutch pressure command and the first derivative with respect to time of the off-going clutch pressure command; 
         FIG. 4  is a schematic depiction of a buffer storing a set of data generated from the off-going clutch pressure command; and 
         FIG. 5  is a block diagram illustrating a k-means neural network algorithm for processing the data in the buffer of  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The control of this invention is described in the context of a multi-ratio power transmission having a planetary gear set of the type described in the U.S. Pat. No. 4,070,927 to Polak, and having an electro-hydraulic control of the type described in U.S. Pat. No. 5,601,506 to Long et al, both of which are hereby incorporated by reference in their entireties. Accordingly, the gear set and control elements shown in  FIG. 1  hereof have been greatly simplified, it being understood that further information regarding the fluid pressure routings and so on may be found in the aforementioned patents. 
     Referring to  FIG. 1 , the reference numeral  10  generally designates a vehicle power train including engine  12 , transmission  14 , and a torque converter  16  providing a fluid coupling between engine  12  and transmission input shaft  18 . A torque converter clutch  19  is selectively engaged under certain conditions to provide a mechanical coupling between engine  12  and transmission input shaft  18 . The transmission output shaft  20  is coupled to the driving wheels of the vehicle in one of several conventional ways. The illustrated embodiment depicts a four-wheel-drive (FWD) application in which the output shaft  20  is connected to a transfer case  21  that is also coupled to a rear drive shaft R and a front drive shaft F, but any driven wheel configuration is within the scope of the present invention. Typically, the transfer case  21  is manually shiftable to selectively establish one of several drive conditions, including various combinations of two-wheel-drive and four-wheel drive, and high or low speed range, with a neutral condition occurring intermediate the two and four wheel drive conditions. 
     The transmission  14  has three inter-connected planetary gear sets, designated generally by the reference numerals  23 ,  24  and  25 . The planetary gear set  23  includes a sun gear member  28 , a ring gear member  29 , and a planet carrier assembly  30 . The planet carrier assembly  30  includes a plurality of pinion gears rotatably mounted on a carrier member and disposed in meshing relationship with both the sun gear member  28  and the ring gear member  29 . The planetary gear set  24  includes a sun gear member  31 , a ring gear member  32 , and a planet carrier assembly  33 . The planet carrier assembly  33  includes a plurality of pinion gears rotatably mounted on a carrier member and disposed in meshing relationship with both the sun gear member  31  and the ring gear member  32 . The planetary gear set  25  includes a sun gear member  34 , a ring gear member  35 , and a planet carrier assembly  36 . The planet carrier assembly  36  includes a plurality of pinion gears rotatably mounted on a carrier member and disposed in meshing relationship with both the sun gear member  34  and the ring gear member  35 . 
     The input shaft  18  continuously drives the sun gear  28  of gear set  23 , selectively drives the sun gears  31 ,  34  of gear sets  24 ,  25  via clutch C 1 , and selectively drives the carrier  33  of gear set  24  via clutch C 2 . The ring gears  29 ,  32 ,  35  of gear sets  23 ,  24 ,  25  are selectively connected to ground  42  via clutches (i.e., brakes) C 3 , C 4  and C 5 , respectively. 
     As diagrammed in  FIG. 2 , the state of the clutches C 1 -C 5  (i.e., engaged or disengaged) can be controlled to provide six forward speed ratios ( 1 ,  2 ,  3 ,  4 ,  5 ,  6 ), a reverse speed ratio (R) or a neutral condition (N). For example, the first forward speed ratio is achieved by engaging clutches C 1  and C 5 . Shifting from one forward speed ratio to another is generally achieved by disengaging one clutch (referred to as the off-going clutch) while engaging another clutch (referred to as the on-coming clutch). For example the transmission  14  is shifted from first to second by disengaging clutch C 5  while engaging clutch C 4 . 
     The torque converter clutch  19  and the transmission clutches C 1 -C 5  are controlled by an electro-hydraulic control system, generally designated by the reference numeral  44 . The hydraulic portions of the control system  44  include a pump  46  which draws hydraulic fluid from a reservoir  48 , a pressure regulator  50  which returns a portion of the pump output to reservoir  48  to develop a regulated pressure in line  52 , a secondary pressure regulator valve  54 , a manual valve  56  manipulated by the driver of the vehicle and a number of solenoid-operated fluid control valves  58 ,  60 ,  62  and  64 . 
     The electronic portion of the electro-hydraulic control system  44  is primarily embodied in the transmission control unit  66 , or controller, which is microprocessor-based and conventional in architecture. The transmission control unit  66  controls the solenoid-operated fluid control valves  58 - 64  based on a number of inputs  68  to achieve a desired transmission speed ratio. Such inputs include, for example, signals representing the transmission input speed TIS, a driver torque command TQ, the transmission output speed TOS, and the hydraulic fluid temperature Tsump. Sensors for developing such signals may be conventional in nature, and have been omitted for simplicity. 
     The control lever  82  of manual valve  56  is coupled to a sensor and display module  84  that produces a diagnostic signal on line  86  based on the control lever position; such signal is conventionally referred to as a PRNDL signal, since it indicates which of the transmission ranges (P, R, N, D or L) has been selected by the vehicle driver. Finally, fluid control valves  60  are provided with pressure switches  74 ,  76 ,  78  for supplying diagnostic signals to control unit  66  on lines  80  based on the respective relay valve positions. The control unit  66 , in turn, monitors the various diagnostic signals for the purpose of electrically verifying proper operation of the controlled elements. 
     The solenoid-operated fluid control valves  58 - 64  are generally characterized as being either of the on/off or modulated type. To reduce cost, the electro-hydraulic control system  44  is configured to minimize the number of modulated fluid control valves, as modulated valves are generally more expensive to implement. To this end, fluid control valves  60  are a set of three on/off relay valves, shown in  FIG. 1  as a consolidated block, and are utilized in concert with manual valve  56  to enable controlled engagement and disengagement of each of the clutches C 1 -C 5  with only two modulated valves  62 ,  64 . For any selected ratio, the control unit  66  activates a particular combination of relay valves  60  for coupling one of the modulated valves  62 ,  64  to the on-coming clutch, and the other one of the modulated valves  62 ,  64  to the off-going clutch. 
     The modulated valves  62 ,  64  each comprise a conventional pressure regulator valve biased by a variable pilot pressure that is developed by current controlled force motors (not shown). Fluid control valve  58  is also a modulated valve, and controls the fluid supply path to converter clutch  19  in lines  70 ,  72  for selectively engaging and disengaging the converter clutch  19 . The transmission control unit  66  determines pressure commands for smoothly engaging the on-coming clutch while smoothly disengaging the off-going clutch to shift from one speed ratio to another, develops corresponding force motor current commands, and then supplies current to the respective force motors in accordance with the current commands. Thus, the clutches C 1 -C 5  are responsive to the pressure commands via the valves  58 - 64  and their respective actuating elements (e.g., solenoids, current-controlled force motors). 
     As indicated above, each shift from one speed ratio to another includes a fill or preparation phase during which an apply chamber of the on-coming clutch is filled in preparation for torque transmission. Fluid supplied to the apply chamber compresses an internal return spring (not shown), thereby stroking a piston (not shown). Once the apply chamber is filled, the piston applies a force to the clutch plates, developing torque capacity beyond the initial return spring pressure. Thereafter, the clutch transmits torque in relation to the clutch pressure, and the shift can be completed using various control strategies. The usual control strategy involves commanding a maximum on-coming clutch pressure for an empirically determined fill time, and then proceeding with the subsequent phases of the shift. The volume of fluid required to fill an apply chamber and thereby cause the clutch to gain torque capacity is referred to as the “clutch volume.” 
     If the predetermined fill time is too short, and the apply chamber is not filled sufficiently, the on-coming clutch does not have sufficient torque capacity when the off-going clutch is released, resulting in engine flare prior to the next phase of the shift; if the predetermined fill time is too long, the on-coming clutch will develop significant torque capacity before the off-going clutch is released, resulting in an early pull-down or a clutch overlap condition (i.e., a tie-up). 
     The controller  66  determines the timing of the pressure commands based on an estimated on-coming clutch volume, i.e., an estimated volume of fluid required to fill the on-coming clutch apply chamber and thereby cause the oncoming clutch to gain torque capacity. An estimated on-coming clutch volume must be used because the actual on-coming clutch volume may vary over time as a result of wear, and may vary from transmission to transmission because of build variations and tolerances. 
     The controller  66  calculates an estimated volume of fluid supplied to the on-coming clutch apply chamber as the chamber is being filled based on a mathematical model of the transmission hydraulic system, and compares the estimated volume of fluid supplied to the estimated clutch volume. When the estimated volume of fluid supplied to the apply chamber equals the estimated clutch volume, then the on-coming clutch should gain capacity. A hydraulic flow model for use in estimating the volume of fluid supplied to an apply chamber is described in U.S. Pat. No. 6,285,942, issued Sep. 4, 2001 to Steinmetz et al, which is hereby incorporated by reference in its entirety. The model inputs include the fill pressure, the shift type ST (for example, a 1-2 upshift), the speed of pump  46 , and the temperature Tsump of the hydraulic fluid. The output of the model is the on-coming clutch flow rate. The flow rate is integrated by an integrator to form the estimated cumulative volume of fluid supplied to the apply chamber. In a preferred embodiment, the controller  66  subtracts the estimated volume of fluid supplied from the estimated clutch volume to determine an estimated clutch volume remaining. If the controller is accurate, the estimated clutch volume remaining will be zero at the time the on-coming clutch gains torque capacity. 
     The controller  66  is programmed to effect a clutch-to-clutch shift by lowering the torque on an off-going clutch to the point of allowing slip, and then closed loop controlling the off-going clutch to maintain a predetermined slip threshold. More specifically, during a shift event, the controller  66  generates an off-going clutch pressure command to which the off-going clutch&#39;s actuating elements are responsive to affect the off-going clutch pressure. The controller uses the input shaft speed signal TIS and the output shaft speed signal TOS to determine the amount of slip on the off-going clutch, and adjusts the magnitude of the off-going clutch pressure command to maintain the predetermined slip threshold, thereby effectuating the closed loop control. 
     During the shift event, the controller  66  also generates an on-coming clutch pressure command sufficient to cause the on-coming clutch to gain torque capacity during the closed loop control of the off-going clutch at the predetermined slip threshold. As the on-coming clutch gains torque capacity, it resists the rotation of the input shaft, causing a reduction in input shaft speed. The controller  66  detects the reduction in input shaft speed, and, because of the closed loop control of the off-going clutch, reduces the magnitude of the off-going clutch pressure command in an effort to maintain the predetermined slip threshold. As the on-coming clutch gains torque capacity, the magnitude of the off-going clutch pressure command becomes smaller until the off-going clutch has no torque capacity and the shift event is completed. 
     The off-going clutch pressure command is therefore responsive to the on-coming clutch gaining torque capacity, and thus may be advantageously analyzed to obtain information about the on-coming clutch. Referring to  FIG. 3 , the off-going clutch pressure command  100 , as measured by the commanded off-going clutch fill pressure, is graphically depicted with respect to time during a shift event. The controller is programmed to determine the first derivative  104  with respect to time of the off-going clutch pressure command  100 , and the second derivative (not shown) with respect to time of the off-going clutch pressure command  100 . Local minima and maxima  108 A-R of the first derivative  104  are found where the second derivative is equal to zero. 
     Each local minimum and maximum  108 A-R is a data point comprising the time value at which the local minimum or maximum occurred and the corresponding value of the first derivative. The controller is programmed to generate a set of data containing the data points  108 A-R for each local minimum and maximum, and a corresponding estimated clutch volume remaining for each of the data points. The data is stored in a buffer  110 , as shown in  FIG. 4 . 
     The closed loop control of the off-going clutch results in a reduction in magnitude of the off-going clutch pressure command when the on-coming clutch gains torque capacity. Accordingly, the first derivative will change from a positive value to a negative value, or from a negative value to a more negative value, when the on-coming clutch gains torque capacity. Thus, data points with a time value earlier than a negative to positive transition in the first derivative are discarded or ignored. In  FIGS. 3 and 4 , the first derivative at local minimum  108 E is negative, and first derivative at local maximum  108 F is positive. Accordingly, all data points associated with local minima and maxima occurring prior to  108 F are ignored or discarded. 
     The controller then performs a k-means neural network algorithm to assign each of the data points  108 F- 108 R into one of two clusters or groups, where one group, “Group 1,” consists of those local minima and maxima that occur before on-coming clutch torque capacity, and where the other group, “Group 2,” consists of those local minima and maxima that occur after on-coming clutch torque capacity. The k-means neural network method employed by the controller is depicted in the flow chart of  FIG. 5 . The method includes selecting a first data point to function as an initial Group 1 Mean (step  112 ). In the preferred embodiment, the controller selects the data point  108 F having the earliest time value of all the remaining data points in the buffer as the initial Group 1 Mean. The method also includes selecting a second data point to function as an initial Group 2 Mean (step  116 ). In the preferred embodiment, the controller selects the data point  108 R having the latest time value of all the data points in the buffer as the initial Group 2 Mean. 
     The method also includes calculating, for each data point  108 F-R in the buffer, the distance between the data point and the Group 1 Mean (step  120 ). The method also includes calculating, for each data point  108 F-R in the buffer, the distance between the data point and the Group 2 Mean (step  124 ). The distance between a data point and a mean may be the Euclidean distance from the data point to the mean. That is,
 
 D =√{square root over (( M   m   −M   DP ) 2 +( t   m   −t   DP ))}{square root over (( M   m   −M   DP ) 2 +( t   m   −t   DP ))} 2  
 
     Where D is the distance between the mean and the data point, M m  is the value of the first derivative at the mean, M DP  is the value of the first derivative at the data point, t m  is the time value at the mean, and t DP  is the time value at the data point. Alternatively, the distance may be non time based, where the distance is simply the difference between the first derivative value of the data point and the first derivative value of the mean. 
     The method further includes classifying the data points that are closer to the Group 1 Mean than the Group 2 Mean into Group 1 (step  128 ), and classifying the data points that are closer to the Group 2 Mean than the Group 1 Mean into Group 2 (step  132 ). Using the data points in Group 1, a New Group 1 Mean is calculated (step  136 ). If the distances calculated in steps  120  and  124  are Euclidean distances, then the New Group 1 Mean will comprise the mean first derivative value and the mean time value of all the data points classified as Group 1. If the distances calculated are non time based, i.e., the difference between a data point&#39;s first derivative value and the mean&#39;s first derivative value, then the New Group 1 Mean will comprise the mean first derivative value of all points classified as Group 1. Similarly, using the data points in Group 2, a New Group 2 Mean is calculated (step  140 ). 
     In decision block  144 , the controller determines whether the Group 1 Mean is equal to the New Group 1 Mean, and whether the Group 2 Mean is equal to the New Group 2 Mean. If not, then the controller designates the New Group 1 Mean as the Group 1 Mean, designates the New Group 2 Mean as the Group 2 Mean (step  148 ), and then repeats the clustering process at step  120 . If so, the k-means neural network algorithm is successfully completed. 
     After the controller has processed the data in the buffer according to the k-means neural network algorithm, the controller determines the data point  108 I in the second group having the earliest time value. Data point  108 I is considered the point at which the on-coming clutch gained capacity, and, accordingly, the point at which the on-coming clutch&#39;s apply chamber is completely filled. The estimated volume remaining associated with point  108 I should be zero, that is, the estimated volume of fluid supplied to the on-coming clutch apply chamber should be equal to the estimated clutch volume. If the estimated volume remaining associated with point  108 I is not zero, then the controller can adapt its volume remaining calculations accordingly. For example, referring again to  FIG. 4 , the estimated clutch volume remaining at data point  108 I is −20 cc. The controller may increase the estimated clutch volume accordingly since the estimated volume of fluid supplied exceeds the estimated clutch volume by 20 cc. 
     While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.