Abstract:
A system for controlling temperature of a transmission clutch includes a housing containing the clutch, a fan for circulating air through the housing and over the clutch, and a controller configured to determine an inferred temperature at a reference surface on the clutch and to actuate the fan in response to the inferred temperature.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to a multiple speed powershift transmission for a motor vehicle. In particular, the invention pertains to controlling temperature of the input clutches for the transmission. 
         [0003]    2. Description of the Prior Art 
         [0004]    A powershift transmission is a geared mechanism producing multiple gear ratios in forward drive and reverse drive and having two input clutches, which connect a power source, such as an engine or electric motor, to two transmission input shafts. 
         [0005]    The transmission incorporates gearing arranged in a dual layshaft configuration between the transmission input and its output. One input clutch transmits torque between the input and a first layshaft associated with first, second, fifth and sixth gears; the other input clutch transmits torque between the transmission input and a second layshaft associated with third, fourth and reverse gears. The transmission produces gear ratio changes by alternately engaging a first input clutch and running in a current gear, disengaging the second input clutch, preparing a power path in the transmission for operation in the target gear, disengaging the first clutch, engaging the second clutch and preparing another power path in the transmission for operation in the next gear. 
         [0006]    Temperature is a critical factor that determines the length of the service life of a dry powershift transmission in which each input clutch is a dry clutch. A principal failure mode is attributable to high clutch temperature, which is a durability predictor for the dual clutch of the powershift transmission. 
         [0007]    Two clutch locations, where the temperature and degradation rate are relevant, include the clutch surface temperature, and a reference point used for temperature monitoring, which is located preferably 4.0 mm under the clutch contact surface. Although these two locations are critical to clutch durability, no direct, real time temperature feedback is available for alerting the driver of potentially abusive harmful usage because thermocouple access and the transmission of data from a thermocouple on a rotating member present technical difficulties. Additionally, when a vehicle equipped with a dual clutch powershift transmission is presented for service with clutch problems, it is difficult to trace the history of the particular problem to its root cause, and to identify possible usage conditions and anomalies. 
         [0008]    A need exists in the industry for a mechanism to alert the operator of a vehicle with a dual clutch powershift transmission of potentially abusive conditions, combined with temperature integration for application severity and history monitoring and cumulative wear as reflected by temperature feedback. 
       SUMMARY OF THE INVENTION 
       [0009]    A system for controlling temperature of a transmission clutch includes a housing containing the clutch, a fan for circulating air through the housing and over the clutch, and a controller configured to determine an inferred temperature at a reference surface on the clutch and to actuate the fan in response to the inferred temperature. 
         [0010]    The invention contemplates a method for controlling the temperature of a clutch. A housing is provided containing a dual input clutch. A fan is provided for circulating air through the housing both internally and externally for forced convection. An inferred temperature on the clutch within the housing is determining and the fan is actuated in response to the inferred temperature. 
         [0011]    The system and method provide a mechanism to modulate temperature on the input clutch of a dual clutch powershift transmission. The temperature of each clutch is determined without requiring that a temperature sensor be placed on a surface of the clutch, which is located in a bell housing to which access is difficult to attain. 
         [0012]    The invention avoids high clutch temperature at various vehicle operating conditions, thereby lengthening the service life of the input clutches and improving their operation. 
         [0013]    The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0015]      FIG. 1  is a schematic diagram showing details of a dual input clutch powershift transmission; 
           [0016]      FIG. 2  is cross sectional view of a bell housing that contains the dual dry input clutches of  FIG. 1 ; 
           [0017]      FIG. 3  is a schematic diagram showing a system for cooling dual dry input clutches of  FIG. 1  located in the bell housing of  FIG. 2 ; 
           [0018]      FIG. 4  is a graph showing the variation of the inferred clutch temperature and a hysteresis temperature band; 
           [0019]      FIG. 5  is a diagram of an algorithm for controlling operation of a fan that reduces the clutch temperature; 
           [0020]      FIG. 6  is schematic diagram showing a TCU, input information supplied as input, and equations used to determine an inferred temperature; and 
           [0021]      FIG. 7  is a schematic diagram of a vehicle powertrain that includes an engine and a dual clutch powershift transmission. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    Referring now to the drawings, there is illustrated in  FIG. 1  a dual dry clutch powershift transmission  10  including a first dry input clutch  12 , which selective connects the input  14  of transmission  10  alternately to the even-numbered gears  16  associated with a first layshaft  18 , and a second dry input clutch  20 , which selective connects the input  20  alternately to the odd-numbered gears  22  associated with a second layshaft  24 . 
         [0023]    Input  14  is driveably connected to a power source such as an internal combustion engine or an electric motor. An electronic transmission control module (TCM) controls the input clutches  12 ,  20  through command signals sent to solenoid-actuated servos, which actuate the input clutches. The TCM includes a microprocessor accessible to electronic memory and containing control algorithms expressed in computer code, which are executed repeatedly at frequent intervals. 
         [0024]    Shaft  18  supports pinions  26 ,  28 ,  30 , which are each journalled on shaft  18 , and couplers  32 ,  34 , which are secured to shaft  18 . Pinions  26 ,  28 ,  30  are associated respectively with the second, fourth and sixth gears. Coupler  32  includes a sleeve  36 , which can be moved leftward to engage pinion  26  and driveably connect pinion  26  to shaft  18 . Coupler  34  includes a sleeve  38 , which can be moved leftward to engage pinion  28  and driveably connect pinion  28  to shaft  18 . Sleeve  38  can be moved rightward to engage pinion  30  and driveably connect pinion  30  to shaft  18 . 
         [0025]    Shaft  24  supports pinions  40 ,  42 ,  44 , which are each journalled on shaft  24 , and couplers  46 ,  48 , which are secured to shaft  24 . Pinions  40 ,  42 ,  44  are associated respectively with the first, third and fifth gears. Coupler  46  includes a sleeve  50 , which can be moved leftward to engage pinion  40  and driveably connect pinion  40  to shaft  24 . Coupler  48  includes a sleeve  52 , which can be moved leftward to engage pinion  42  and driveably connect pinion  42  to shaft  24 . Sleeve  52  can be moved rightward to engage pinion  44  and driveably connect pinion  44  to shaft  24 . 
         [0026]    Output  54  supports gears  56 ,  58 ,  60 , which are each secured to shaft  54 . Gear  56  meshes with pinions  26  and  40 . Gear  58  meshes with pinions  28  and  42 . Gear  60  meshes with pinions  30  and  44 . 
         [0027]    Couplers  32 ,  34 ,  46  and  48  may be synchronizers, or dog clutches or a combination of these. 
         [0028]      FIG. 2  illustrates a bell housing  70  formed with a shell  72 , in which input clutches  12 ,  20  are located, and fins  74  extending radial from an axis  76 , which is coaxial with input  14  and output  54 . At least two fins  74  are interconnected at their radial outer edge by a cylindrical shell  78 , which forms an annular air jacket or duct  80 . 
         [0029]      FIG. 3  is a schematic diagram showing a system  90  for cooling the dual dry input clutches  12 ,  20  and the bell housing  70 . A fan  92  forces incoming ambient air through an inlet  94  to a splitter  96 , which direct a portion of the incoming air across the interior of the bell housing  70  and over the surfaces of the clutches  12 ,  20  to an outlet  98 . A residual portion of the incoming air is directed by the splitter  96  into external ducting  80 , in which fins  74  are located. Air exits the duct  80  through outlet  98  and is returned to the ambient atmosphere. 
         [0030]    Empirical data obtained by bench testing, which simulates in-service operation of clutches  12 ,  20 , is used to correlate the temperature indicated by a thermocouple  100  on the bell housing  70  and the temperature of the critical surfaces  102 ,  104  of the input clutches  12 ,  20 , respectively, and surfaces about 4 mm below the clutch surfaces  102 ,  104 . In this way, data produced by thermocouple  100  is a reference from which the temperature of the critical clutch surfaces  102 ,  104  can be inferred. 
         [0031]      FIG. 1  show a transmission control unit (TCU)  106 , which controls operation of fan  92  in accordance with a control algorithm expressed in computer code, stored in electronic memory and executed by a microprocessor incorporated in the TCU. An electric motor  108  activates and deactivates fan  92  in response to electric power carried on line  110  from a source of electric power  112  to the motor  198  subject to a switching function provided by the TCU  106  in accordance with the algorithm. 
         [0032]      FIG. 4  graphically illustrates the variation of the clutch temperature T infer  at clutch surfaces  102 ,  104  as inferred from an electronic signal  114  produced by thermocouple  100  and transmitted as input to TCU  106 . The graph shows an upper limit temperature T ul , a lower limit temperature T II  and a hysteresis temperature band  110  between the upper and lower limits to avoid cycling the fan  92  around a set temperature. 
         [0033]      FIG. 5  is a diagram of the algorithm that controls operation of fan  92 . At step  120  a test is made to determine whether the difference between the inferred clutch temperature T infer  and the upper limit temperature T ul  is greater than zero. If the result of test  120  is logically true, at step  122 , fan  92  is turned on by the TCU  106  electrically connecting the power source  112  and the electric motor  110 . 
         [0034]    If the result of test  120  is logically false, the control algorithm advances to step  124  where a test is made to determine whether the difference between the inferred clutch temperature T infer  and the lower limit temperature T II  is less than zero. If the result of test  124  is logically true, at step  126 , fan  92  is turned off by the TCU  106  electrically disconnecting the power source  112  and the electric motor  110 . 
         [0035]    If the results of tests  120  and  124  are both logically false indicating that the inferred clutch temperature T infer  is in the hysteresis band  110 , the control algorithm advances to step  128  where the operating state of fan  92  is maintained unchanged, whereupon the algorithm returns to step  120  and is re-executed. 
         [0036]    Instead of using temperature data from thermocouple  100  as a reference from which the temperature of the critical clutch surfaces  102 ,  104  can be inferred, an alternate technique, described with reference to  FIGS. 6 and 7 , can be used to infer that temperature. 
         [0037]    Input information supplied to the TCU  106  includes engine speed and engine torque  130  transmitted to input  14  from an engine or other power  132  source driveably connected to the input  14 . An engine control module (ECM)  133  monitors engine speed and repeatedly at frequent intervals determines from engine operating variables the magnitude of torque produced by the engine  132 . The speed and torque  134  transmitted by output  54  of transmission  10  to the driven wheels  136  is input repeatedly at sampling intervals to the TCU  106 . 
         [0038]    Additional input information  138  supplied to the TCU  106  repeatedly at sampling intervals includes the specific heat of the clutches  12 ,  20 , the rate of heat convection from the clutches, and the weight and thermal conductivity of the clutches. Further input information  140  supplied to the TCU  106  repeatedly at sampling intervals includes the ambient temperature, coefficient of friction (COF) of the clutch surfaces  102 ,  104 , and initial temperature of the clutches. 
         [0039]    As  FIG. 6  shows, TCU  106  uses these input data and information stored in electronic memory to calculate the rate of change of rotating power absorbed by the clutches  12 ,  20  due to clutch input power (Q in ); the magnitude of heat energy absorbed by the clutches (Q s ) due to a change of clutch temperature ΔT; the rate at which heat energy is carried from the critical surfaces  102 ,  104  of the clutches by conduction (Q c ) due to a temperature difference (T 1 −T 2 ); the rate at which heat energy is carried from the critical surfaces  102 ,  104  of the clutches by convection (Q v ) due to a temperature difference (T 1 −T 2 ); the net heat change at the critical surfaces of the clutches (Q s ) during a period whose length is Δtime; and the change in the inferred temperature at the critical surfaces of the clutches during a sampling interval (T i+1 ). 
         [0040]    M is the symbol for mass, Lambda for conductivity, A for convective area, l for length of the conductive element, and Alpha for heat transfer coefficient. Power expressed in watts is 
         [0000]      Power= T   slip *( N   in   −N   out )*π/30 
         [0041]    The algorithm illustrated in  FIG. 5  that controls operation of fan  92  is used to actuate the fan when the inferred temperature of the critical surfaces  102 ,  104  is determined as described with reference  FIG. 6 . At step  120  a test is made to determine whether the difference between the inferred clutch temperatures T i+1  and the upper limit temperature T ul  is greater than zero. If the result of test  120  is logically true, at step  122 , fan  92  is turned on by the TCU  106  electrically connecting the power source  112  and the electric motor  110 . 
         [0042]    If the result of test  120  is logically false, the control algorithm advances to step  124  where a test is made to determine whether the difference between the inferred clutch temperatures T i+1  and the lower limit temperature T II  is less than zero. If the result of test  124  is logically true, at step  126 , fan  92  is turned off by the TCU  106  electrically disconnecting the power source  112  and the electric motor  110 . 
         [0043]    If the results of tests  120  and  124  are both logically false indicating that the inferred clutch temperature T i+1  is in the hysteresis band  110 , the control algorithm advances to step  128  where the operating state of fan  92  is maintained unchanged, whereupon the algorithm returns to step  120  and is re-executed. 
         [0044]    In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.