Abstract:
A method for detecting a clutch fault of an automatic transmission includes determining a current clutch energy density of a clutch during a range shift and comparing the current clutch energy density to a first energy density threshold. A diagnostic alert is activated if the current clutch energy density exceeds the first energy density threshold.

Description:
FIELD OF THE INVENTION 
     The present invention relates to automatic transmissions, and more particularly to detecting a clutch fault in an automatic transmission. 
     BACKGROUND OF THE INVENTION 
     A vehicle powerplant produces drive torque that is transferred through a transmission to a driveline. The automatic transmission includes a number of clutches that are selectively engaged and disengaged to provide one of several speed ratios between input and output shafts. The input shaft is coupled to the vehicle&#39;s powerplant through a torque converter. The input shaft drives the output shaft through a gear set. The output shaft is coupled to the driveline to drive wheels of the vehicle. 
     Shifting from a current speed ratio to another speed ratio involves disengaging an engaged clutch or off-going clutch and engaging another clutch or on-coming clutch. During a shift, a clutch fault may occur. For example, failure of the off-going clutch to fully disengage can cause clutch tie-up. Failure of the on-coming clutch to engage can cause clutch flare. Clutch tie-up results in the on-coming clutch absorbing greater amounts of shift energy and can eventually lead to component failure. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides a method for detecting a clutch fault of an automatic transmission. The method includes determining a current clutch energy density of a clutch during a range shift and comparing the current clutch energy density to a first energy density threshold. A diagnostic alert is activated if the current clutch energy density exceeds the first energy density threshold. 
     In one feature, the method further includes comparing the current clutch energy density to a second energy density threshold that is greater than the first energy density threshold. Default range shifting is activated if the current clutch energy density exceeds the second energy density threshold. 
     In other features, determining the current clutch energy density includes determining energy into the clutch and determining energy out of the clutch. A difference between the energy into and the energy out of the clutch is calculated. The difference is divided by an area of the clutch. 
     In other features, determining the energy into the clutch includes determining torque across the clutch and determining slip across the clutch. Determining the energy out of the clutch includes determining a difference between a clutch temperature and a transmission fluid temperature. 
     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 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic illustration of a vehicle including an exemplary automatic transmission that is controlled by the clutch fault detection system of the present invention; 
         FIG. 2  is a table illustrating exemplary clutch engagement combinations to achieve various speed ratios of the exemplary automatic transmission; and 
         FIG. 3  is an exemplary flowchart illustrating steps performed by the clutch fault detection system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment 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 execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , the reference numeral  100  generally designates a motor vehicle including a powerplant  102 , a torque converter  104  and an exemplary multiple speed automatic transmission  110 . The powerplant  102  produces drive torque and includes, but is not limited to, an internal combustion engine, an electric machine and a combination thereof (e.g., hybrid electric vehicle). The torque converter includes a pump  106  and a turbine  108 . The exemplary transmission  110  includes a plurality of hydraulically actuated clutches C 1 , C 2 , C 3 , C 4 , and C 5 , that enable, for example, six speed ranges. Speed range shifts are accomplished by selectively engaging and disengaging select clutches. The motor vehicle  100  also includes a driveline  118 , a range selector  128 , a control module  134 , control valves  132  and a hydraulic pressure source  138 . 
     Referring now to  FIG. 2 , 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  110  includes six forward drive ratios and one reverse drive ratio, it is appreciated that the clutch fault detection system of the present invention can be implemented in automatic transmissions having more or fewer drive ratios. The table of  FIG. 2  illustrates an exemplary combination of engaged clutches to establish the various drive ratios. 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  110  is in neutral when only the fifth clutch C 5  is engaged. 
     Each drive ratio requires the engagement of different combinations of the multiple clutches. Further, shifting between successive forward ratios is accomplished by disengaging one of the clutches, deemed the off-going clutch, and substantially simultaneously engaging the next clutch, deemed the on-coming clutch, while another clutch is engaged during the transition. For example, given the exemplary transmission described above, shifting from the first drive ratio to the second drive ratio is achieved by keeping clutch C 1  engaged, disengaging clutch C 5  and engaging clutch C 4 . 
     Referring back to  FIG. 1 , the powerplant  102  drives the torque converter  104  via a shaft  112  and the torque converter  104  drives the transmission  110  via a shaft  114 . The transmission  110  includes an output shaft  116  that drives the driveline  118 . A first speed sensor  115  is responsive to a rotational speed of the input shaft  114  and generates an input shaft speed signal. A second speed sensor  117  is responsive to a rotational speed of the output shaft  116  and generates an output shaft speed signal. A temperature sensor  119  is responsive to a temperature of a transmission fluid and generates a transmission fluid temperature signal. 
     The speed and torque relationships between the powerplant  102  and the driveline  118  are controlled by the hydraulically operated clutches C 1 , C 2 , C 3 , C 4 , and C 5 . Pressurized fluid is provided to the clutches and the torque converter  104  from a regulated hydraulic pressure source  130 . The clutches C 1 , C 2 , C 3 , C 4 , and C 5  are coupled to the source  130  via the control valves  132 , which regulate clutch pressure by supplying or discharging fluid to/from the clutches C 1 , C 2 , C 3 , C 4 , and C 5 . 
     Operation of the pressure source  130  and the control valves  132  is controlled by the control module  134  in response to various input signals. The input signals include, but are not limited to, the input shaft speed signal (N T ), the output shaft speed signal (N O ), the transmission fluid temperature signal (F t ) and a range selector position signal that is generated by the range selector  128 . The control module  134  generates control signals based on the input signals to energize the select control valves  132  to achieve a desired drive ratio. The control signals regulate the hydraulic pressure supplied by the control valves  132 . Clutch pressure effects shifting between speed ratios by controllably releasing the pressure in an off-going clutch and controllably applying pressure to the on-coming clutch. 
     When tie up or flare occurs during a shift, there is an increase in clutch energy (ΔE). ΔE is defined as the difference between the energy into the clutch (E i ) during shift and the energy out of the clutch (E o ) during the shift:
 
Δ E=E   i   −E   o  
 
The energy E i  going into the clutch can be calculated as the product of clutch torque (T c ) and slip speed (S c ) across the clutch integrated over the shift time:
 
 E   i =∫( T   c   ×S   c ) dt  
 
The shift time is the time that is required to complete the shift.
 
     The clutch torque T c  is calculated based on the clutch pressure (p c ), the clutch area (A c ), the clutch return spring force (F c ), a known friction coefficient (f) for the clutch and constants k 1  and k 2 . k 1  and k 2  are calibration constants that can be determined from respective look-up tables.
 
 T   c   =k   1   ×p   c   A   c   −k   2 ×f×F c  
 
     The clutch slip speed S c  can be determined from the following equation:
 
 S   c   =g   1   ×N   T   −g   2   ×N   O ,
 
where g 1  and g 2  are known factors that are based on the transmission gear design and the shift ratio. The energy E o  going out of the clutch can be calculated as a function of a heat transfer coefficient (h) times the difference in a predicted clutch temperature (C t ) and the transmission fluid temperature (F t ):
 
 E   o   =h× ( C   t   −F   t )
 
C t  can be determined based on transmission operating parameters from a model or a look-up table.
 
     A clutch energy density (ED) is defined as ΔE divided by the clutch area A c . The clutch fault detection system determines the status of the clutch, as an indication of clutch fault, which can be imminent (short term) or impending (longer term). The clutch fault detection system selectively activates a default gear shift procedure or issues a diagnostic alert or other warnings depending on the severity of the detected fault. 
     An exemplary flowchart of the steps performed by the clutch fault detection system are illustrated in  FIG. 3 . In step  200 , the clutch data is input and includes all the parameters used to calculate ED during a current clutch shift. The current ED is calculated in step  202 . In step  204 , the historical or average clutch ED is updated based on the current clutch ED. The average clutch ED is determined over a predetermined number of shifts N s  using clutch ED values that have been stored in memory. For example, if N s  is selected as 10, then the current clutch ED and the previous nine clutch ED values are used to calculate the new average clutch ED. In this example, the current clutch ED is associated with the latest shift (e.g., number 10). The previous clutch ED values associated with number 9-10 drop their orders by one. The previous clutch ED associated number 1 is removed and is not used in future calculations of the average clutch ED. 
     The current clutch ED is compared to an imminent ED threshold value in step  206  to determine whether a clutch failure is imminent (i.e., shorter term). If the current clutch ED is not greater than the imminent ED threshold, control continues in step  208 . If the current clutch ED is greater than the imminent ED threshold, control issues an imminent failure alert in step  210  and ends. The current clutch ED is compared to an impending ED threshold value in step  208  to determine whether a clutch failure is impending (i.e., longer term). The impending ED threshold is less than the imminent ED threshold. If the current clutch ED is not greater than the impending ED threshold, control continues in step  212 . If the current clutch ED is greater than the impending ED threshold, control issues an impending failure alert in step  214  and ends. 
     In step  212 , control determines whether the average clutch ED exceeds an average ED threshold. If the average clutch ED is less than the average ED threshold, control ends. If the average clutch ED is greater than the average ED threshold control issues a maintenance alert in step  216 . The imminent failure alert, impending failure alert and maintenance alert can each be visual, audible or both. 
     In a further aspect of the present invention, the clutch energy densities ED for each clutch C 1 , C 2 , C 3 , C 4 , and C 5  over a selected number of range shifts or driving time can be summed to provide a cumulative clutch ED. The cumulative clutch ED can be compared to a cumulative clutch ED threshold to provide warnings for diagnostic purposes. The cumulative clutch ED can be stored in memory and can be used to provide historical data for the performance of the transmission fluid and the automatic transmission  110 . It is also anticipated that a default control can be implemented to provide a limp-home mode of vehicle operation along with one or each of the various failure alerts. The default control can limit engine operation (e.g., limit maximum engine speed) and/or limit transmission operation (e.g., limit selectable gear ratios) to avoid potential damage to the transmission. 
     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, the specification and the following claims.