Abstract:
A control system includes a pressure control solenoid and a flow control solenoid having an input in fluid communication with the pressure control solenoid. A piston adjusts a position of a shift fork and includes a first area in fluid communication with the pressure control solenoid and a second area in fluid communication with the flow control solenoid. A fork sensor senses a position of a shift fork. A slip sensing module estimates slip acceleration between an input shaft and a gear. A flow determining module generates a flow command for the flow control solenoid. A sync control module determines a slip acceleration profile including an estimated slip acceleration, adjusts the estimated slip acceleration based on the measured slip acceleration, and generates a pressure command for the pressure control solenoid based on the adjusted slip acceleration.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/324,515, filed on Apr. 15, 2010, which is hereby incorporated by reference in its entirety. 
     This application is related to U.S. patent application Ser. Nos. 12/850,159 filed on Aug. 4, 2010, and 12/850,083 filed on Aug. 4, 2010. The disclosures of the above applications are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates to dual clutch transmissions, and more particularly to a control system and method for synchronization control in dual clutch transmissions. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     When a driver wants to change from one gear to another in a car with a manual transmission, the driver depresses a clutch pedal. The clutch disconnects the engine and interrupts power flow. Then the driver uses a manual stick shift to select another gear. The manual stick shift is connected by a mechanical linkage assembly to shift forks. The shift forks are attached to gear selectors, which deselect one gear and select another gear. 
     The gear selectors may include synchronizers to match a speed of the gear selector to the gear to prevent grinding. Once the new gear is engaged, the driver releases the clutch pedal to re-connect the engine and transmit power to the wheels. 
     As can be appreciated from the foregoing, manual transmissions do not provide a continuous flow of power from the engine to the wheels. Instead, power delivery changes from on to off (when the clutch is disengaged) and from off to on (when the clutch is engaged and the transmission is in gear). As can be appreciated, a loss of efficiency and reduced performance occurs during periods when the manual transmission is disengaged. Furthermore, the on/off nature of power delivery provided by the manual transmission can be annoying. 
     A dual-clutch transmission (DCT) uses two clutches but does not include a clutch pedal. One clutch may be used to control a first subset of gears (such as first, third, and fifth) while the other clutch may be used to control a second subset of the gears (such as second, fourth and sixth). Using this arrangement, a different gear can be preselected before the shift to prevent interruption in the power flow from the engine to the transmission. As a result, efficiency and performance is improved. 
     A powertrain control module and a hydraulic control system may be used to control operation of the clutches, shift forks and gear selectors. It is difficult to control the shift forks during synchronization and engagement or disengagement of the gear selectors. As a result, some DCTs may generate a banging noise when shifting. Furthermore, a significant amount of time and effort may be needed to calibrate the powertrain control module and hydraulic control system to shift with acceptable shift quality and speed. 
     SUMMARY 
     A control system includes a pressure control solenoid and a flow control solenoid having an input in fluid communication with the pressure control solenoid. A piston adjusts a position of a shift fork and includes a first area in fluid communication with the pressure control solenoid and a second area in fluid communication with the flow control solenoid. A fork position sensor senses a position of a shift fork. A slip sensing module estimates slip acceleration between an input shaft and a gear. A flow determining module generates a flow command for the flow control solenoid. A sync control module determines a slip acceleration profile including an estimated slip acceleration, adjusts the estimated slip acceleration based on the measured slip acceleration, and generates a pressure command for the pressure control solenoid based on the adjusted slip acceleration. 
     In other features, the sync control module includes a slip acceleration module that generates the slip acceleration profile based on an initial slip acceleration and a predetermined sync time. The sync control module further includes an error module that generates a slip acceleration error based on the estimated slip acceleration and the measured slip acceleration. The sync control module further includes a summing module that generates the adjusted slip acceleration based on the estimated slip acceleration and the slip acceleration error. The sync control module further includes a force converter module that generates a force command based on the adjusted slip acceleration. 
     In other features, the sync control module further includes a pressure converter module that generates the pressure command based on the force command. The slip acceleration profile includes a first portion that ramps to a maximum value, a second portion that is constant at the maximum value, and a third portion that ramps towards zero at a first rate. The second area is larger than the first area. The shift fork is moved from a neutral position to a sync position. The flow command is a constant flow command during synchronization. 
     In still other features, the systems and methods described above are implemented by a computer program executed by one or more processors. The computer program can reside on a tangible computer readable medium such as but not limited to memory, nonvolatile data storage, and/or other suitable tangible storage mediums. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIGS. 1 and 2  are functional block diagrams of a control system for a dual clutch transmission; 
         FIG. 3  is a functional block diagram of a sync module according to the present disclosure; 
         FIG. 4  is a flowchart illustrating a method for syncing a shift fork according to the present disclosure; 
         FIG. 5  illustrates synchronizer slip and an absolute slip acceleration profile during synchronization; and 
         FIG. 6  illustrates synchronizer slip, the absolute slip acceleration profile, an actual acceleration profile, and a pressure command. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     The present disclosure relates to control systems and methods for controlling fork actuators in a DCT during synchronization. In some implementations, fork actuators include two-sided pistons. A flow control (FC) solenoid may be connected to one side of the piston and a pressure control (PC) solenoid may be connected to the other side of the piston. The PC solenoid may feed the FC solenoid. 
     During synchronization, force is controlled to the piston of the fork actuator by setting the FC solenoid to a constant value and varying the pressure command to the piston using the PC solenoid. During synchronization, a shaft acceleration profile is calculated to bring a slip speed of the synchronizer from a level at the beginning of the synchronization event to zero during a predetermined period. The force that is commanded is a function of commanded shaft acceleration and synchronizer characteristics. The present disclosure allows smooth control of synchronization events in DCTS within a predetermined amount of time with minimal calibration effort. 
     During the synchronization event, the flow control solenoid is set to a constant level and the pressure control solenoid is used to apply a force to the synchronizer. The force reduces the slip between the input shaft and the gear to zero. The synchronizer slip is a function of the measured output speed of the transmission, the measured speed of the shaft that the synchronizer rotates on, and the gear ratio between the two. 
     When the synchronizer slip is reduced to zero, the synchronization event is complete. In order to complete synchronization, a slip acceleration profile is commanded that is a function of the slip at the beginning of the event and the calibrated time to complete the event. This profile is shaped by a ramp from the rate that slip is changing at the beginning of the event to the maximum acceleration and a ramp at the end from maximum acceleration to zero. These ramps are calibrated as percentages of the total calibrated synchronization time. 
     The shaft acceleration command is then converted to a force command as a function of reflected inertia and synchronizer capacity. The force command is then sent to the pressure control solenoid as a pressure command. The pressure command is equal to the force divided by the area of the piston that is being acted on. A closed loop approach is used to ensure that the actual shaft acceleration follows the commanded profile. The closed control loop uses the rate of change of the synchronizer slip as a feedback and makes corrections based on the difference between the commanded profile and the actual acceleration. 
     In some implementations, the two sides of the fork actuator pistons have different areas. The FC solenoid may be connected to a larger area of the two sides. The PC solenoid may be connected to a smaller area of the two sides. The PC solenoid also feeds pressure to the FC solenoid attached to the other side of the fork actuator piston. 
     Referring now to  FIGS. 1 and 2 , an exemplary control system  10  for the DCT is shown. A pump  14  pumps a fluid through a filter  16 . A bypass  18  may be provided around the filter  16 . An output of the filter  16  is supplied to an accumulator  20 . A check ball  19  may be arranged between the filter  16  and the accumulator  20 . An output of the accumulator  20  passes through a heat sync  22  before being supplied to pressure control (PC) solenoids  28 - 1 ,  28 - 2 ,  28 - 3  and  28 - 4  (collectively PC solenoids  28 ). 
     An output of the PC solenoid  28 - 1  is fed to a flow control (FC) solenoid  30 - 1 . An output of the FC solenoid  30 - 1  is fed to a clutch  34 - 1 . A clutch position sensor (CPS)  36 - 1  senses a position of the clutch  34 - 1 . In some implementations, the clutch  34 - 1  may be associated with odd gears of the DCT. 
     An output of the PC solenoid  28 - 2  is fed to a FC solenoid  30 - 2 . An output of the FC solenoid  30 - 2  is fed to a clutch  34 - 2 . A CPS  36 - 2  senses a position of the clutch  34 - 2 . In some implementations, the clutch  34 - 2  may be associated with even gears of the DCT. 
     An output of a PC solenoid  28 - 3  is fed to a first logic valve  50 - 1 . The output of the PC solenoid  28 - 3  is also fed to an FC solenoid  30 - 3 . An output of the FC solenoid  30 - 3  is fed to the first logic valve  50 - 1 . Outputs of the logic valve  50 - 1  are fed to a first fork actuator  52 - 1  and a second fork actuator  52 - 2 , respectively. First and second fork actuators  52 - 1  and  52 - 2  include first and second pistons  54 - 1  and  54 - 2 , respectively. First and second shift forks  56 - 1  and  56 - 2  are connected to ends of the first and second pistons  54 - 1  and  54 - 2 , respectively. First and second fork position sensors  58 - 1  and  58 - 2  sense a position of the shift forks  56 - 1  and  56 - 2 , respectively. 
     An output of a PC solenoid  28 - 4  is fed to a second logic valve  50 - 2 . The output of the PC solenoid  28 - 4  is also fed to an FC solenoid  30 - 4 . An output of the FC solenoid  30 - 4  is fed to the second logic valve  50 - 2 . Outputs of the second logic valve  50 - 2  are fed to a third fork actuator  52 - 3  and a fourth fork actuator  52 - 4 , respectively. Third and fourth fork actuators  52 - 3  and  52 - 4  include third and fourth pistons  54 - 3  and  54 - 4 , respectively. Third and fourth shift forks  56 - 3  and  56 - 4  are connected to ends of the third and fourth pistons  54 - 3  and  54 - 4 , respectively. Third and fourth fork position sensors  58 - 1  and  58 - 2  sense a position of the shift forks  56 - 3  and  56 - 4 , respectively. 
     Various check balls  60 - 1 ,  60 - 2  and  60 - 3  may be used as shown in the hydraulic circuits supplying the clutches  34 - 1  and  34 - 2 . A secondary logic valve solenoid  62  receives fluid from the check ball  60 - 1  and supplies flew in to the second logic valve  50 - 2  and the first logic valve  50 - 1  via the second logic valve  50 - 2 . For example, the shift fork  56 - 1  moves a gear selector  70  back and forth along a shaft  76  between gears  72  and  74 . 
     In  FIG. 2 , a control module  80  communicates with the fork position sensors  58 - 1 ,  58 - 2 ,  58 - 3  and  58 - 4 , the PC solenoids  28 - 1 ,  28 - 2 ,  28 - 3  and  20   8 - 4 , the FC solenoids  30 - 1 ,  30 - 2 ,  30 - 3  and  30 - 4 , the clutch position sensors  36 - 1  and  36 - 2 , the first and second logic valve&#39;s  50 - 1  and  50 - 2 , the secondary logic about  62  and the pressure sensor  24 . The control module  80  controls positions of the clutches and shift forks as will be described further below to effectuate shifting of the DCT. Additional inputs may include a transmission output speed sensor (TOSS)  92 , and shaft speed sensor(s)  94  that sense speeds of one or more shafts on which the gear selectors reside. 
     Referring now to  FIG. 3 , an exemplary sync module  100  according to the present disclosure is shown. The sync module  100  may be implemented in the control module  80  in  FIG. 2  or any other control module associated with the vehicle. The sync module  100  includes a sync slip acceleration module  110  that generates a command slip acceleration based on an initial sync slip and a predetermined sync time. 
     An error module  114  receives actual slip acceleration and the slip acceleration command and generates a slip acceleration error. The slip acceleration command and the slip acceleration error are output to a summing module  118 . The summing module  118  generates a difference between the slip acceleration command and the slip acceleration error. The summing module outputs an adjusted slip acceleration to a force converter module  122 , which converts the adjusted slip acceleration to a force. A pressure converter module  124  converts the force to a pressure command for the PC solenoid. 
     A fork velocity module  128  generates a fork velocity based upon fork position. A sync complete module  132  determines when sync is complete based upon a least one of fork position, fork velocity and actual slip acceleration. When one or more of the sync complete conditions are present, the sync enable signal to the pressure converter module  124  goes low or the sync module is otherwise disabled. 
     Referring now to  FIG. 4 , a method  150  for syncing a shift fork according to the present disclosure is shown. At  154 , an initial sync slip and sync period are determined. At  158 , a sync acceleration command is generated. At  162 , a slip acceleration error is determined. At  164 , the slip acceleration command is adjusted based on the slip acceleration error. At  168 , a pressure command is calculated based upon the adjusted slip acceleration command. At  172 , control determines whether the synchronization is complete. If not, control returns to  158 . Otherwise, control ends. 
     Referring now to  FIG. 5 , synchronizer slip  200  and an absolute slip acceleration profile  204  are shown during synchronization. The ramp rate at  226  provides a smooth transition of slip speed at  222 . The time required to reach maximum slip acceleration is shown at  208 . The percentage of the total time to decrease to a final slip acceleration is shown at  214 . The total time required to complete the synchronization event is shown at  218 . 
     Referring now to  FIG. 6 , synchronizer slip  200  and an absolute slip acceleration profile  204  are shown during synchronization. An actual absolute acceleration profile  240  is shown. A pressure command  250  is adjusted based on feedback to smooth slip acceleration. 
     The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.