Abstract:
A method for controlling trapped air in a clutch of an automatic clutch-to-clutch transmission includes, calculating a pulse on time based on a clutch volume and adaptive convergence. A pulse off time is calculated based on a temperature of transmission fluid. A pulse number is calculated based on the temperature of transmission fluid. A maximum pressure is commanded to the clutch based on the pulse on time and a minimum pressure is then commanded to the clutch based on the pulse off time. A pulse counter is incremented when the pulse off time expires. The steps of commanding maximum pressure, then commanding minimum pressure, and incrementing the pulse counter are repeated until the pulse counter equals a desired pulse number.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to transmission control systems and methods, and more particularly to transmission control systems and methods that purge air from a clutch of the transmission.  
       BACKGROUND OF THE INVENTION  
       [0002]     In an automatic transmission control valves supply hydraulic pressure to clutches and bands to engage each gear. A pump draws fluid from a sump in the bottom of the transmission and feeds it to the hydraulic system. Once the clutch is no longer required to be applied, the fluid is drained back to the sump. When the transmission is in park, neutral, or the engine is turned off, the pressurized fluid can be completely drained from the clutch and collected in a sump.  
         [0003]     During this time, rotating clutches in a clutch-to-clutch transmission experience drain down issues that cause air to get into the clutch. Despite a bleed orifice, air becomes entrapped in the clutch. The trapped air causes the first shifts after complete drain down to flare. In order to eliminate air entrapped in the clutch it is desirable to purge air from the clutch of the transmission.  
       SUMMARY OF THE INVENTION  
       [0004]     Accordingly, a method for controlling trapped air in a clutch of an automatic clutch-to-clutch transmission includes, calculating a pulse on time based on a learned clutch volume and an adaptive convergence state. A pulse off time and a pulse number are calculated based on a temperature of transmission fluid. A maximum pressure is commanded to the clutch based on the pulse on time and a minimum pressure is then commanded to the clutch based on the pulse off time. A pulse counter is incremented when the pulse off time expires. The steps of commanding maximum pressure, commanding minimum pressure, and incrementing the pulse counter are repeated until the pulse counter equals a desired pulse number.  
         [0005]     In other features, the method is performed if enable conditions are met, and wherein the enable conditions are met if the method has not been performed during a key cycle. Alternatively, enable conditions are met if the transmission has operated in a range park or neutral for a selected period of time.  
         [0006]     In another feature, the method is performed if the transmission is operating in a desired gear.  
         [0007]     In still other features, the method comprises delaying a current upshift of the transmission while repeating is being performed, wherein delaying the upshift is not performed if engine speed indicates an overspeed condition.  
         [0008]     In yet other features, subsequent upshifts are delayed after repeating is complete. Delaying is performed for each subsequent upshift, and wherein each subsequent upshift is delayed for a selectable amount of time. Delaying subsequent upshifts is not performed if engine speed indicates an overspeed condition.  
         [0009]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0011]      FIG. 1  is a schematic illustration of a vehicle including an air purge system according to the present invention;  
         [0012]      FIG. 2  is a chart illustrating the required clutches to be engaged in order to achieve a desired gear for a six speed clutch-to-clutch transmission;  
         [0013]      FIG. 3  is a data flow diagram illustrating a control module of the air purge system; and  
         [0014]      FIG. 4  is a flowchart illustrating steps performed by the control module. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, 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 term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.  
         [0016]     Referring now to  FIG. 1 , a vehicle is shown generally at  10 . The vehicle includes an engine  12  that drives a transmission  14  through a torque converter  16 . Air is drawn into the engine  12  through a throttle  18 . The air is mixed with fuel and combusted within cylinders (not shown) of the engine  12  to produce drive torque. The torque converter  16  supplies the engine torque to the transmission via an input shaft  20 . The transmission  14  in the exemplary embodiment is a multi-speed, automatic, clutch-to-clutch transmission that drives an output shaft  22  based on engine torque.  
         [0017]     The output shaft  22  drives a driveline  24  of the vehicle  10 . A range selection device  26  enables an operator to set the transmission  14  at a desired operating range including, but not limited to, park, reverse, neutral, and one or more forward drive positions. The speed and torque relationships between the engine  12  and the driveline  24  are controlled by hydraulically operated clutches C 1 , C 2 , C 3 , C 4 , and C 5  of the transmission  14 . Pressurized fluid is provided to the clutches from a regulated hydraulic pressure source  28 . The clutches C 1 , C 2 , C 3 , C 4 , and C 5  are coupled to the hydraulic pressure source via control valves  30 , which regulate clutch pressure by supplying or discharging fluid to/from the clutches C 1 , C 2 , C 3 , C 4 , and C 5 .  
         [0018]     Referring now to  FIG. 2 , in the exemplary transmission, the five clutches C 1 , C 2 , C 3 , C 4  and C 5  are selectively engaged to provide neutral, six forward drive ratios, and one reverse drive ratio. Although the exemplary automatic transmission  14  includes six forward drive ratios and one reverse drive ratio, it is appreciated that the air purge method and system for a rotating clutch according to the present invention can be implemented in automatic transmissions having more or fewer drive ratios.  
         [0019]     The table of  FIG. 2  illustrates an exemplary combination of engaged clutches to establish the various drive ratios. Each drive ratio relates to an automatic gear of the transmission where the gears for a six speed automatic transmission are first, second, third, fourth, fifth and sixth. The first forward drive ratio is established by engaging the first clutch C 1  and the fifth clutch C 5 . The second forward drive ratio is established by disengaging the fifth clutch C 5  and substantially simultaneously engaging the fourth clutch C 4 . To establish the third forward drive ratio, the fourth clutch C 4  is disengaged as the third clutch C 3  is engaged. The fourth forward drive ratio is established by disengaging the third clutch C 3  while engaging the second clutch C 2 . To establish the fifth forward drive ratio, the first clutch C 1  is disengaged as the third clutch C 3  is substantially simultaneously engaged. The sixth forward drive ratio is established by disengaging the third clutch C 3  and simultaneously engaging the fourth clutch C 4 . The reverse drive ratio is established by engaging the third clutch C 3  and the fifth clutch C 5 . The transmission  14  is in neutral when only the fifth clutch C 5  is engaged.  
         [0020]     Referring back to  FIG. 1 , a speed sensor  32  senses a rotational speed of the engine  12  and generates an engine speed signal. A temperature sensor  36  senses a temperature of the transmission fluid and generates a transmission temperature signal. The range selection device  26  generates a range signal. A control module  40  receives the above mentioned signals. The control module  40  controls the operation of the control valves  30  in order to pulse on and off clutches of the transmission  14 . The control module  40  pulses a clutch based on the received signals and the air purge method of the present invention. In an exemplary embodiment, the control module  40  pulses C 3  a determined number of times while the transmission  14  is operating in first and second gear, before the transmission  14  reaches third gear.  
         [0021]     Referring to  FIG. 3 ,  FIG. 3  is a data flow diagram illustrating sub-modules and data-flows of the control module  40  of the present invention. The control module  40  includes an enable module  42 , a gear enable module  44 , a pulse determination module  46 , a clutch pressure module  48 , and a shift delay module  50 . The enable module  42  receives the range signal  52  from the range selection device  26  ( FIG. 1 ). The enable module  42  determines whether the air purge method has already run this key cycle. If the air purge method has not run, the enable module enables the air purge method by setting an enable flag  54  to TRUE. If the air purge method has already run once this key cycle but the transmission range  52  indicates park or neutral for a selectable period of time during the key cycle, the enable module  42  re-enables the air purge method by setting the enable flag  54  to TRUE.  
         [0022]     Gear enable module  44  receives a transmission gear  56  determined from the ratio of the transmission  14  ( FIG. 1 ) and the enable flag  54  from enable module  42 . Gear enable module  44  evaluates the transmission gear  56 . If the enable flag  54  is TRUE and the transmission  14  ( FIG. 1 ) is operating in a proper gear to enable pulsing of a clutch, gear enable module  44  enables the pulse determination module  46  by setting a pulse enable flag  58  to TRUE. Pulse determination module  46  receives the transmission temperature  60 , a current calculated line pressure  62 , and the enable flag  58 . Pulse determination module  46  calculates a pulse on time  66  from a learned volume of the clutch and a state of convergence to the volume. The learned volume of the clutch and the state of convergence of the volume are calculated based on the transmission temperature  60  and the current line pressure  62 . Pulse determination module  46  also calculates a pulse off time  68  and an adequate pulse number  70  based on the transmission temperature  60 .  
         [0023]     Clutch pressure module  48  receives the pulse on time  66 , the pulse off time  68 , and the pulse number  70 . Clutch pressure module  48  commands line pressure  72  at a maximum value according to the pulse on and off times  66 , 68  and the number of pulses  70 . Clutch pressure module keeps a pulse count  74  of the number of pulses completed. Shift delay module  50  receives engine speed sensed from the engine  12  ( FIG. 1 ), the transmission gear  56 , and the pulse count  74 . If the pulse count  74  is not equal to a desired number of pulses for the current gear  56 , shift delay module  50  delays the transmission  14  ( FIG. 1 ) from shifting to the next higher gear (upshifting) by sending a commanded gear signal  78  to maintain the current gear. Shift delay module  50  delays the shift as long as the engine speed  76  does not indicate an overspeed condition. Shift delay module  50  further delays subsequent upshifts after the pulse count  74  indicates the pulses have completed to ensure adequate shift spacing.  
         [0024]     Referring now to  FIG. 4 , a flowchart illustrating steps of the air purge method according to the present invention is shown. The air purge method is continually performed throughout a key cycle. In step  100 , control determines whether enable conditions are met. If a new key cycle has occurred or the range indicates park or neutral for a selected period of time, enable conditions are met and control continues with step  110 . Otherwise control loops back and continues to monitor the enable conditions. In step  110 , control determines whether the transmission is operating in the proper gear to pulse the clutch on and off. In the example of pulsing C 3  on and off, the proper gears would be first gear and second gear. If the transmission is in the proper gear, control continues with step  120 .  
         [0025]     In step  120 , control calculates a pulse on and off time and pulse number based on a learned clutch volume, an adaptive convergence state, and the transmission temperature. In step  130 , control commands maximum pressure. If the pulse on time has expired in step  140 , control continues with step  150 . If the pulse on time has not expired in step  140 , control continues commanding maximum pressure in step  130 . Once the pulse on time has expired, control commands pressure off in step  150 .  
         [0026]     In step  160 , control determines whether a desired number of pulses has completed for that gear. If the desired number of pulses has not completed, control delays an upshift from occurring in step  170  by commanding the current gear to be maintained. Control then evaluates the pulse off time in step  180 . If the pulse off time has not expired control continues to command pressure off in step  150 . If the pulse off time has expired, control increments a pulse counter in step  186  and loops back to step  120  where a new pulse on and off time and pulse number is calculated. Control then continues to pulse the clutch on and off until a desired number of pulses has completed.  
         [0027]     In step  160 , if the pulse counter equals the desired number of pulses, the upshift is allowed in step  190  and the pulse values are reset to zero in step  200 . Control then loops back to step  110  where the transmission gear is evaluated. If the transmission is still operating in the proper gear for pulsing, control continues to pulse the clutch as stated in the steps above. Otherwise, the transmission  14  ( FIG. 1 ) has shifted to a gear in which pulsing of the clutch is not desired. In the exemplary embodiment, this is third gear because C 3  is required to be fully applied for the operation of third gear. Once the transmission  14  ( FIG. 1 ) is not operating in the desired gear, control delays any subsequent upshifts based on the time delay created by the pulsing in step  210 . This delay time can be selectable. The delay prevents undesireable shifts occurring one right after another. Control then loops back to step  100  where the enable conditions are evaluated.  
         [0028]     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.