Patent Publication Number: US-2019195292-A1

Title: Clutch Local Peak Temperature Real Time Predictor and Applications

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to friction clutches in work machines, and more particularly, to apparatus and methods for predicting local peak temperatures in friction clutches and controlling the friction clutches to reduce failure and to predict preventative maintenance timing. 
     BACKGROUND 
     Machines such as articulated haul trucks and off-highway mining trucks include an engine that provides power to wheels of the trucks via a planetary-type transmission. A planetary-type transmission is generally made up of at least three different elements, including a sun gear, a planet carrier having at least one set of planet gears, and a ring gear. The planet gears of the planet carrier mesh with the sun gear and the ring gear. One of the sun gear, planet carrier and ring gear is driven as an input to the transmission, while another of the sun gear, planet carrier, and ring gear rotates as an output of the transmission. The sun gear, planet carrier, planet gears, and ring gear can all rotate simultaneously to transmit power from the input to the output at a first ratio of speed-to-torque and in a forward direction or, alternatively, one of the sun gear, planet carrier, and ring gear can be selectively held stationary or locked to rotate with another gear and thereby transmit power from the input to the output at a second ratio of speed-to-torque and/or in a reverse direction. The change in rotational direction and/or speed-to-torque ratio of the transmission depends upon the number of teeth in the sun and ring gears, the gear(s) that is selected as the input, the gear(s) that is selected as the output, and which gear, if any, is held stationary or rotationally locked with another gear. A hydraulic clutch (also commonly referred to as a brake) is used to hold particular gears stationary and/or to lock the rotation of particular gears together. 
     The clutches in the transmission typically rely on frictional forces for their operation. The purpose of friction clutches is to connect a moving member to another that is moving at a different speed or stationary, often to synchronize the speeds, and/or to transmit power. The friction clutches include plates connected to and rotating with each of the connected components. The plates are pressed together by a device such as a hydraulic piston with sufficient force to create frictional engagement between the plates to cause the connected components to rotate together. As little slippage as possible between the engaged plates is desired. However, because friction is involved in locking the clutches, heat is generated in the clutches. It is possible for the heat to rise to a level that can cause damage to the components of the clutches. Moreover, repeated heating cycles in the clutches over time can cause degradation of the components and the performance of the clutches so that periodic maintenance or replacement is necessary before the clutches fail during operation of the machine. Therefore, the clutch temperature of clutches can be a key indicator of clutch durability and performance. 
     Systems exist for determining and monitoring clutch temperatures in friction clutches. An example of such a system is provided in U.S. Pat. No. 8,879,979, issued to Hebbale et al. on Nov. 25, 2014, entitled “Thermal Model for Dry Dual Clutch Transmission” (“&#39;979 patent”). The reference discloses a method of determining temperatures for a dry dual clutch mechanism including one or more steps, such as determining a first heat input from a first clutch and determining a second heat input from a second clutch. The second clutch is separated from the first clutch by a center plate. The method also includes determining a housing air temperature of housing air within a bell housing case of the dry dual clutch mechanism. A thermal model is applied with the determined first heat input and second heat input. The thermal model includes temperature states for at least the first clutch, the second clutch, and the center plate. From the thermal model, the method determines at least a first clutch temperature and a second clutch temperature. The method includes executing a control action with the determined first clutch temperature and second clutch temperature. 
     Prior art systems such as that shown in the &#39;979 patent typically utilize energy dissipation and average temperature distributions to monitor friction clutches. However, friction clutches experience peak temperatures at localized areas within the friction clutches, typically at locations on the clutch plates. The existence of local peak temperatures, also known as thermoelastic instability (TEI), is typically not accounted for in the prior art systems. The omission of the local peak temperatures leads to the underestimation of the clutch temperature so that the prior art systems can fail to accurately predict the clutch durability and performance, and thereby increase the risk of clutch failures during operation of the machine. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect of the present disclosure, a method for determining a local peak temperature for a friction clutch in a machine and controlling engagement of the friction clutch using the local peak temperature, wherein the local peak temperature is a temperature at a hot spot of the friction clutch. The method may include determining current operating parameter values of operating parameters of the machine, determining a current local peak temperature for the friction clutch based on the current operating parameter values, comparing the current local peak temperature for the friction clutch to a critical peak temperature for the friction clutch, maintaining engagement of the friction clutch in response to determining that the current local peak temperature is less than the critical peak temperature, and disengaging the friction clutch in response to determining that the current local peak temperature is greater than the critical peak temperature. 
     In another aspect of the present disclosure, a machine. The machine may include an engine, traction devices, a friction clutch operatively connecting the engine to the traction devices and selectively engageable to transmit torque output by the engine to the traction devices, a friction clutch actuator operatively connected to friction clutch and actuatable in response to a clutch control current to selectively engage and disengage the friction clutch, and an electronic control module (ECM) operatively connected to the engine and the friction clutch. The ECM may be programmed to determine current operating parameter values of operating parameters of the machine, determine a current local peak temperature for the friction clutch based on the current operating parameter values, compare the current local peak temperature for the friction clutch to a critical peak temperature for the friction clutch, transmit the clutch control current to the friction clutch actuator to maintain engagement of the friction clutch in response to determining that the current local peak temperature is less than the critical peak temperature, and cease transmitting the clutch control current to the friction clutch actuator to disengage the friction clutch in response to determining that the current local peak temperature is greater than the critical peak temperature. 
     In a further aspect of the present disclosure, a method for determining a local peak temperature for a friction clutch in a machine and controlling engagement of the friction clutch using the local peak temperature, wherein the local peak temperature is a temperature at a hot spot of the friction clutch. The method may include detecting operating parameters of the machine, inputting operating parameter values corresponding to the operating parameters into a surrogate model of the friction clutch, determining, in the surrogate model, a current local peak temperature for the friction clutch, outputting, from the surrogate model, the current local peak temperature for the friction clutch, comparing the current local peak temperature for the friction clutch to a critical peak temperature for the friction clutch, maintaining engagement of the friction clutch in response to determining that the current local peak temperature is less than the critical peak temperature, and disengaging the friction clutch in response to determining that the current local peak temperature is greater than the critical peak temperature. 
     These and additional aspects are defined by the claims of this patent. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an exemplary machine having a multi-clutch transmission in which clutch local peak temperature real time prediction in accordance with the present disclosure can be implemented; 
         FIG. 2  is a table depicting exemplary gear combinations for the transmission of  FIG. 1 ; 
         FIG. 3  is a schematic illustration of an exemplary hydraulic circuit including clutch actuators for friction clutches of the transmission of  FIG. 1 ; 
         FIG. 4  is a block diagram of control components that may implement clutch local peak temperature real time prediction in accordance with the present disclosure in the machine and transmission of  FIG. 1 ; 
         FIG. 5  is a plan view of an exemplary clutch plate for the clutches of the transmission in the machine of  FIG. 1  indicating exemplary locations of hot spots; 
         FIG. 6  is a flow diagram of a friction clutch surrogate model development routine in accordance with the present disclosure; 
         FIG. 7  is a flow diagram of a local peak temperature prediction and friction clutch control routine in accordance with the present disclosure; and 
         FIG. 8  is a flow diagram of a proactive friction clutch maintenance routine in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an exemplary machine  10  is schematically illustrated in which real time prediction of clutch local peak temperatures and clutch control in accordance with the present disclosure may be implemented. The machine  10  includes an exemplary transmission  12  having a plurality of friction clutches for control of shifting the transmission  12  between available forward and reverse gears. The machine  10  may be a mobile machine that may perform predetermined tasks at a worksite. For example, the machine  10  may embody a mobile machine such as an off-highway mining truck, a wheel loader, a motor grader, an articulated haul truck, or any other mobile machine known in the art. The worksite may include, for example, a mine site, a landfill, a quarry, a construction site, or another type of worksite. The predetermined tasks performed by the machine  10  may require the machine  10  to traverse the worksite between different destinations. Accordingly, the transmission  12  may be a component of a power train of the machine  10  that facilitates travel between the different destinations at the worksite. 
     The power train of the machine  10  may generally include an engine  14  and the transmission  12 . The engine  14  may embody any type of engine known in the art, for example, a diesel, gasoline, or gaseous-fuel powered, internal combustion engine configured to generate a mechanical power output. The transmission  12  may include an input member  16  such as an input shaft connecting the transmission  12  to the mechanical power output of the engine  14  via a torque converter  18 , for example, and an output member  20  connecting the transmission  12  to one or more traction devices  22 , such as wheels or tracks. As will be described in more detail below, the transmission  12  may embody a mechanical step-change transmission having at least one reverse gear and a plurality of forward gears. Each of the different gears may be manually or automatically selected by an operator to provide a different ratio of speed-to-torque in either the forward or reverse travel directions. 
       FIG. 1  schematically illustrates one half of the transmission  12  located to the side of a rotational axis of symmetry (axis)  24 . The input member  16  and the output member  20  may be aligned along the axis  24 . The transmission  12  may generally include a stationary housing  26  and four different planetary gear assemblies  30 ,  32 ,  34 ,  36  disposed within the housing  26  and rotatably supported and aligned along the axis  24 . It is contemplated that the transmission  12  could include a greater or lesser number of planetary gear assemblies, as desired to provide the necessary gears to drive the machine  10  over the worksite. The structure of the different gears, input members, output members and connections there between can be achieved using conventional components, and those skilled in the art will understand that alternative transmission assembly arrangements may have local peak temperature real time prediction and clutch control in accordance with the present disclosure implemented therein. 
     In the disclosed embodiment, each of planetary gear assemblies  30 - 36  may include multiple interconnected components. Specifically, each of planetary gear assemblies  30 - 36  may include a sun gear  40 - 46 , a planet carrier  50 - 56 , and a ring gear  60 - 66 , respectively. The sun gear  40  of the planetary gear assembly  30  may be fixed to rotate with the input member  16  via a coupling  70 , while the ring gear  60 , also of the planetary gear assembly  30 , may be fixed to rotate with the planet carrier  52  of the planetary gear assembly  32  via a coupling  72 . The ring gear  62  of the planetary gear assembly  32  may be fixed to rotate with the sun gears  44  and  46  of the planetary gear assemblies  34 ,  36  via a coupling  74 . The sun gear  42  of the planetary gear assembly  32  may be fixed to rotate with the ring gear  64  of the planetary gear assembly  34  via a coupling  76 . Finally, the ring gear  66  of the planetary gear assembly  36  may be fixed to rotate with the output member  20  via a coupling  78 . 
     The transmission  12  may also include a plurality of friction clutches  80 - 90  selectively actuated to exert torque on portions of the couplings  70 - 78 , the sun gears  40 - 46 , the planet carriers  50 - 56 , and/or the ring gears  60 - 66  that resist relative rotations between components and thereby rotationally lock the components to each other and/or to housing  26  in a variety of different configurations. These connections may facilitate a modification of the speed-to-torque ratio and/or the rotational direction received at the input member  16  relative to the speed-to-torque ratio and rotational direction delivered to the output member  20 . 
     In the disclosed embodiment, the transmission  12  includes six different friction clutches  80 - 90 . It is contemplated, however, that the transmission  12  could include a greater or lesser number of friction clutches, as desired. The friction clutch  80  may be configured to selectively connect the planet carrier  56  with the planet carrier  50 . The friction clutch  82  may be configured to selectively connect the planet carrier  56  to the coupling  70 , that is, to the input member  16  and the sun gear  40 . The friction clutch  84  may be configured to selectively connect the planet carrier  50  to the coupling  74 , that is, to the sun gears  44 ,  46  and the ring gear  62 . The friction clutch  86  may be configured to selectively connect the coupling  76 , that is, the sun gear  42  and the ring gear  64 , to the housing  26 . The friction clutch  78  may be configured to selectively connect the planet carrier  54  to the housing  26 . The friction clutch  90  may be configured to selectively connect the planet carrier  56  to the housing  26 . 
       FIG. 2  illustrates a truth table  92  describing possible engagement combinations of the friction clutches  80 - 90 , which establish ten forward gear ratios and one reverse gear ratio between the input member  16  and the output member  20  by way of the planetary gear assemblies  30 - 36 . For example, to achieve the first forward gear ratio, the friction clutches  80 ,  86 ,  90  are shown to be simultaneously actuated to engage the corresponding components and thereby rotationally lock the corresponding components. Similarly, to achieve the fourth forward gear ratio, the friction clutches  80 ,  84 ,  88  are shown to be simultaneously actuated to engage and rotationally lock the corresponding components. In another example, the reverse gear ratio is shown to be achieved by simultaneously actuating the friction clutches  84 ,  86 ,  90  to engage and rotationally lock the corresponding components. 
     As shown in  FIG. 3 , the friction clutches  80 - 90  may be selectively supplied with hydraulic fluid to engage and connect the corresponding components described above. In particular, the transmission  12  may include a pump  100  configured to draw fluid from a low pressure supply  102 , pressurize the fluid, and direct the pressurized fluid in parallel to the friction clutches  80 - 90  by way of a manifold  104  and a plurality of distribution lines  106 ,  108 ,  110 ,  112 ,  114 ,  116 , respectively. Each of the friction clutches  80 - 90  may include one or more interior actuating chambers that, when filled with the pressurized fluid, displaces one or more pistons moving the piston(s) toward one or more clutch plates (not shown). As a piston “touches up” to a clutch plate, the actuating chamber(s) of the friction clutch  80 - 90  is full of fluid and the friction clutch  80 - 90  is engaged to rotationally lock the corresponding components. As described in connection with  FIG. 2  above, the combination of engaged friction clutches  80 - 90  may determine the gear and the rotational direction of transmission  12 . 
     A plurality of clutch control valves  120 ,  122 ,  124 ,  126 ,  128 ,  130  may be disposed within the distribution lines  106 - 116 , respectively, between the manifold  104  and the corresponding friction clutches  80 - 90 . The clutch control valves  120 - 130  may be selectively energized, based on operator or automatic transmission controller commands, to regulate flows of pressurized fluid to the interior actuating chambers of the friction clutches  80 - 90 . In one example, each of the clutch control valves  120 - 130  may include a two-position, two-way valve mechanism (not shown) that is solenoid operated to actuate one or more of the friction clutches  80 - 90  in response to receiving a clutch control current. Each of the valve mechanisms may be movable between an open or flow-passing position at which fluid is allowed to flow into an associated actuating chamber, and a closed or flow-blocking position at which fluid flow is blocked from the actuating chamber. It is contemplated that each clutch control valve  120 - 130  may include additional or different mechanisms, if desired, such as a proportional valve mechanism, a pilot valve mechanism configured to control a pressure of the fluid entering the two-position valve mechanisms and interior actuating chamber of the associated clutch or clutches, or any other mechanisms known in the art. It is further contemplated that a single clutch control valve  120 - 130  may be associated with more than one of friction clutches  80 - 90 , and vice versa. A pressure relief valve  132  may be disposed within the manifold  104  downstream of the distribution lines  106 - 116  and configured to selectively pass fluid to the low pressure supply  102  in response to a pressure of the fluid within the manifold  104  exceeding a predetermined threshold. 
     The clutch control valves  120 - 130  are among the components that form machine control systems for the machine  10 . Referring to  FIG. 4 , an exemplary arrangement of electrical and control components of the power train of the machine  10  is shown with various control components that may be integrated into real time clutch local peak temperature prediction and clutch control in accordance with the present disclosure. An electronic control module (ECM)  140  may be capable of processing information received from monitoring and control devices using software stored at the ECM  140 , and outputting command and control signals to the clutch control valves  120 - 130  and other devices of the machine  10 . The ECM  140  may include a processor  142  for executing a specified program, which controls and monitors various functions associated with the machine  10 . The processor  142  may be operatively connected to a memory  144  that may have a read only memory (ROM)  146  for storing programs, and a random access memory (RAM)  148  serving as a working memory area for use in executing a program stored in the ROM  146 . Although the processor  142  is shown, it is also possible and contemplated to use other electronic components such as a microcontroller, an application specific integrated circuit (ASIC) chip, or any other integrated circuit device. 
     While the discussion provided herein relates to the functionality of a clutch and transmission control system, the ECM  140  may be configured to control other aspects of the operation of the machine  10  such as, for example, steering, dumping loads of material, actuating implements and the like. Moreover, the ECM  140  may refer collectively to multiple control and processing devices across which the functionality of the clutch and transmission control system and other systems of the machine  10  may be distributed. For clarity in the present example, the electrical and control components include an engine ECM  150  that may have a similar configuration as the ECM  140  and have an engine governor control module stored in memory that is executed to control the operation of the engine  14  in response to operator commands to provide power to drive the traction devices  22  and other working components of the machine  10 . The ECMs  140 ,  150  may be operatively connected to exchange information as necessary to control the operation of the machine  10 . Other variations in consolidating and distributing the processing of the ECMs  140 ,  150  as described herein are contemplated as having use in clutch and transmission control in accordance with the present disclosure. 
     The electronic and control components of the machine  10  may include sensing devices providing information to the ECMs  140 ,  150  for monitoring the status of components and systems of the machine  10  and executing control functions. The sensing devices may include sensors providing information about the current operational state of the power train of the machine  10 . In general, such sensing devices may include speed, torque and position sensors transmitting signals corresponding to the rotational speeds, loads on and angular positions of various rotating components of the machine  10 . Of particular relevance to the present clutch and transmission control strategy are component speed sensors. Consequently, the ECM  140  may be operatively connected to a transmission input speed sensor  152  and a transmission output speed sensor  154 , among other speed sensing devices. The transmission input speed sensor  152  is operatively connected to the transmission input member or shaft  16  and transmits transmission input speed signals with values indicating the rotational speed of the transmission input shaft  16 . The transmission output speed sensor  154  is operatively connected to the transmission output member or shaft  20  and transmits transmission output speed signals with values indicating the rotational speed of the transmission output shaft  20 . 
     In a similar manner, the engine ECM  150  may be operatively connected to an engine output speed sensor  156 . The engine output speed sensor  156  is operatively connected to the output shaft of the engine  14  and transmits engine output speed signals with values indicating the rotational speed of the engine output shaft. The engine output speed signals may be used by the engine governor control module in controlling the engine speed and power output. As may be necessary for clutch and transmission control, the engine output speed signals may be transmitted from the engine ECM  150  to the ECM  140  via an appropriate communication link as known in the art. 
     The ECMs  140 ,  150  are also operatively connected to various output and control device that may be the operational and controllable elements of the machine  10  for propulsion and braking, among other machine functions, that are controlled based on the information from the sensors  152 - 156 . The output and control devices can include clutch actuator devices such as the clutch control valves  120 - 130  discussed above. The clutch control valves  120 - 130  are operatively connected to the ECM  140  for transmission of clutch control current to cause the clutch control valves  120 - 130  to open and allow the pressurized hydraulic fluid to flow to and cause engagement of the corresponding friction clutches  80 - 90 . 
     The output and control devices may further include an engine governor  158 . The engine governor  158  may be integrated into the engine  14  and may be a mechanical governor, an electronic governor implemented in software, or other appropriate conventional engine output control mechanism and control strategy. As illustrated, the engine governor  158  may be operatively connected to and receive engine control signals from the engine ECM  150  to cause the engine governor  158  increase, decrease or maintain the engine output speed and/or power output as dictated by operator inputs. The engine governor control module of the engine ECM  150  may determine values of operating parameters necessary for the engine  14  to produce a commanded output, such as fuel flow rates, intake air flow rates, engine output shaft speeds and the like, and transmit information in the engine control signals to cause the engine governor  158  to operate the engine  14  as commanded. As discussed further below, information related to the control of the engine governor  158  and, correspondingly, the engine  14  may be utilized in the clutch local peak temperature prediction and clutch control strategies in accordance with the present disclosure. Such information may be transmitted from the engine ECM  150  to the ECM  140  as necessary for execution of those strategies. 
     Under ideal conditions, the friction clutches  80 - 90  would heat uniformly such that energy dissipation in the friction clutches  80 - 90  may be used to calculate an average temperature distribution across the clutch components. However, the friction clutches  80 - 90  are sliding systems involving two or more sliding bodies, such as clutch plates, and frictional contact. Heat is not necessarily generated uniformly across the sliding bodies. Uneven heat generation produces non-uniform thermal-elastic distortion and further non-uniformity in the contact pressure distribution. When the sliding speed is sufficiently high, eventually the frictional load and heat generation can localize in a small region or regions of the contact area of the sliding surfaces in a phenomenon known as thermoelastic instability (TEI). 
       FIG. 5  illustrates an example of TEI in a component of one of the friction clutches  80 - 90 . A clutch plate  170  of one of the friction clutches  80 - 90  may be disk-shaped and have an annular outer edge  172  and an annular inner edge  174  defining a central opening. A planar surface  176  faces and contacts a corresponding planar surface  176  of another clutch plate  170  when the corresponding friction clutch  80 - 90  is engaged, and the planar surfaces  176  may slide relative to each other when in contact and thereby generate frictional heat. Lines  178  on the planar surface  176  of the clutch plate  170  are isotherms illustrating an exemplary heat distribution across the planar surface  176 . In general, the lines  178  proximate the outer edge  172  and the inner edge  174  represent cooler temperatures, with the temperatures represented by the lines  178  increasing as they move from the edges  172 ,  174  into the body of the clutch plate  170 . 
     In the illustrated example, a plurality of hot spots  180  may form where the friction between the planar surfaces  176  is greatest and the local peak temperatures are at their maximum. The local peak temperatures at the hot spots  180  can be significantly greater than the average temperature that can be determined from the energy dissipation of the friction clutches  80 - 90 . The cumulative effect of the high local peak temperatures at the hot spots  180  can lead to the need to replace the friction clutches  80 - 90  sooner than anticipated based on the clutch average temperatures. The methods and apparatus of the present disclosure provide a more accurate prediction of the operating conditions of the friction clutches  80 - 90  so that maintenance and replacement can be scheduled at the appropriate time during the useful life of the friction clutches  80 - 90 . 
     INDUSTRIAL APPLICABILITY 
     Several steps or components may be necessary to effectively utilize local peak temperatures to control the operation of clutches such as the friction clutches  80 - 90  and predict when maintenance or replacement may be necessary. First, a surrogate model of the friction clutch  80 - 90  can be developed that can determine the local peak temperatures based on the operating parameters associated with the friction clutch  80 - 90 . With the surrogate model developed, the surrogate model may be used in real time at the ECM  140  to monitor the local peak temperatures and control the operation of the friction clutches  80 - 90  to prevent the local peak temperatures from exceeding a critical temperature above which the friction clutches  80 - 90  may be damaged. Finally, in addition to contemporaneous control, the local peak temperatures may be accumulated and analyzed over time to predict when the friction clutches  80 - 90  will require maintenance or replacement. These components are addressed in systems and apparatus in accordance with the present disclosure. 
       FIG. 6  illustrates an exemplary surrogate model generation routine  200  for building a surrogate model of one of the friction clutches  80 - 90  that will yield a local peak temperature from machine operating parameters of the friction clutches  80 - 90 . The routine  200  may begin at a block  202  where a detailed, fully coupled thermal-mechanical finite element analysis (FEA) model is created that will simulate the clutch engagement process. The thermal-mechanical FEA model can be developed in the manner known in the art using any appropriate finite element software package that allows input and analysis of both mechanical and thermodynamic properties of the modeled device. The finite element software package may be a commercially available package, such as ANSYS®, ADINA®, Autodesk® Simulation and the like, or a custom developed software package. 
     With the thermal-mechanical FEA model developed, control may pass to a block  204  where Design of Experiments (DOE) are conducted using the thermal-mechanical FEA model at various levels of operating conditions to determine peak temperature locations or hot spots within the FEA model of the friction clutch  80 - 90 . Operating conditions relevant to frictional engagement and heat generation that will occur in the friction clutch  80 - 90  may be entered into the FEA model to cause the FEA model to calculate local temperatures in the friction clutch  80 - 90 . Relevant operating parameters can include the pressure in the clutch actuator forcing contact between the clutch plates  170  when the corresponding clutch control valve  120 - 130  is partially or fully open, torque loads on the components, and other conditions affecting the frictional engagement between clutch plates  170  and heat generation within the friction clutch  80 - 90 . Each combination of input operating conditions will result in temperatures being calculated by the FEA model for the friction clutch  80 - 90 . The output temperature distributions will provide indications of the locations of hot spots  180  with local peak temperatures within the friction clutch  80 - 90 . 
     After the DOE simulations are performed for a variety of operating conditions and theoretical local peak temperature locations are identified, control may pass to a block  206  where laboratory tests are conducted on the friction clutch design to determine if the actual local peak temperatures occur at the theoretical locations. It is typically not practical to directly measure the temperature at locations within the friction clutch  80 - 90  such as the hot spots  180  on the clutch plate  170  when the transmission  12  is in the field, but such measurements can be made in the testing environment. Laboratory test may be run using the most relevant sets of operating conditions from the FEA model simulations. For example, operating conditions that resulted in local peak temperatures approximately equal to the critical temperature may be used. Alternatively or in addition, operating conditions providing the clearest indication of the locations of the hot spots  180  may be used. In further alternatives, any other set of operating conditions that are expected to generate meaningful test results can be used. 
     After the laboratory tests are performed and the test data is compiled at the block  206 , control may pass to a block  208  where the laboratory test results are compared to the DOE simulation results to determine if the FEA model correlates to the friction clutch(es) used in the laboratory tests. The goal is to have the FEA model output match the actual thermal characteristics in the friction clutches  80 - 90 . Consequently, the relevant thermodynamic test data is compared to the corresponding FEA simulation results. For example, the locations of the hot spots  180  with high local peak temperatures measured during the laboratory tests are compared to the hot spots  180  from the FEA simulations. If the hot spot locations from the tests differ from the hot spot locations from the FEA simulations by more than a statistically relevant distance, the FEA model may require adjustments to shift the hot spot locations in the simulations. As another example, the values of the local peak temperatures from the laboratory tests may be compared to the values from the FEA simulations. If the local peak temperatures in the test data are significantly higher or lower than in the FEA simulation, the thermodynamic material properties used for the components may require adjustment to move the local peak temperatures in the FEA simulations toward the local peak temperatures in the test data. Additional thermodynamic test data may be correlated with the FEA simulation results to determine whether additional adjustments to the FEA model are necessary. 
     If it is determined at the block  208  that the test data does not correlate to the FEA simulation results, control may pass to a block  210  where the parameters of the FEA model are adjusted as necessary to make the FEA model match the actual friction clutch  80 - 90 . As suggested above, the adjustments can include those necessary to change the hot spot locations in the FEA model, to increase or decrease the local peak temperatures determined during the simulations, and any other changes to the thermal-mechanical properties necessary to match the FEA simulation results to the test data. After the FEA model is adjusted at the block  210 , control may pass to a block  212  where simulations may be performed using the updated FEA model and various operating conditions in a similar manner as described for the original FEA model at the block  204 . 
     As shown in the illustrated embodiment, after simulations are run on the updated FEA model at the block  212 , control may pass back to the block  208  to compare the new FEA simulation results to the test data from the laboratory tests performed at the block  206 . The comparison may be performed and the test data and simulations evaluated in a similar manner as described above. In alternative embodiments, control may pass from the block  212  back to the block  206  before the laboratory test may be performed to generate updated test data based on the most relevant sets of operating conditions from FEA simulations performed with the updated FEA model. In either embodiment, the test data and the FEA simulation results are compared as described above. If the FEA simulation results still do not correlate to the test data, the routine  200  may continue to iterate through FEA model adjustments at the block  210  and subsequent FEA model simulations at the block  212  until the FEA simulation results are sufficiently correlated to the laboratory test data. 
     When the simulation results are determined to correlate to the test data at the block  208 , control may pass to a block  214  were a new DOE is executed with the correlated FEA model to generate a large amount of simulation data. In the new DOE, a wider range of operating condition combinations are used with the correlated FEA model than were executed with the FEA model at the block of  204 . The operating conditions used in the new DOE can range from the most benign conditions at which minimal friction and heat generation occur to the harshest operating conditions where it may be expected that the local peak temperatures at the identified hot spots  180  will greatly exceed the critical temperature for the friction clutch  80 - 90 . The results data generated from the new DOE simulations may provide a comprehensive view of the response of the friction clutch  80 - 90  across the spectrum of potential operating conditions that may be experienced in the field. 
     After the comprehensive simulation data is generated at the block  214 , control may pass back to a block  216  where a surrogate model for the friction clutch  80 - 90  is generated using the simulation results from the block  214 . The simulation data is used to train a machine learning process, such as a neural network or other type of machine-learning technique known in the art, to generate a surrogate model that can be executed in real time by the ECM  140  of the machine  10  to predict local peak temperatures in the friction clutch  80 - 90  under the current operating conditions. During the training, the machine learning process performs the necessary calculations on the simulation data to identify the critical combinations of operating conditions and streamline the local peak temperature discriminations that will be performed by the ECM  140 . The resulting surrogate model when implemented in the ECM  140  of the machine  10  will receive values of the relevant operating parameters of the machine, process the operating parameter values using animal processing resources, and output local peak temperatures for the relevant locations within the friction clutch  80 - 90 . 
     As discussed, operating parameter values of relevant operating parameters will be input into the surrogate model generated at the block  216  to determine the local peak temperatures of the friction clutch  80 - 90  in real time. Some of the relevant operating parameters may be readily measured and input to the surrogate model. For example, the rotational speeds of the input member or shaft  16  and the output member or shaft  20  may be measured by the transmission speed sensors  152 ,  154  discussed above and have the sensed speeds input to the surrogate model. Other operating parameter values are not readily directly measured in real time. For example, it may not be practical to place a pressure sensor inside the friction clutch  80 - 90  to sense a pressure in a hydraulic piston. Also, torque of the engine output shaft that determines a load on the friction clutch  80 - 90  may not be able to be directly measured without reducing the torque and the efficiency of the engine  14 . Consequently, such operating parameter values must be derived from other measurable or known operating parameters. 
     When such derivations are required, control of the routine  200  may pass to a block  218  where operating parameter conversions are determined. Each of the operating parameters requiring derivation may have a corresponding conversion from measurable parameters developed. For example, a clutch pressure forcing the clutch plates  170  of the friction clutch  80 - 90  into engagement is generated based on the clutch control current transmitted to the corresponding clutch control valve  120 - 130 . Consequently, a relationship will exist between the clutch control current and the clutch pressure. This relationship can be expressed in the conversion as a lookup table, a mathematical function or other expression wherein a clutch control current value is input and a clutch pressure is output for subsequent input to the surrogate model. The load on the friction clutch  80 - 90  may be calculated from the output torque of the engine  14  which, as discussed above, is not directly measured. However, the engine output torque can be calculated from engine operating parameters that are known to the engine ECM  150 , such as the fuel flow rate from the engine governor control module and the engine output speed from the engine output speed sensor  156 . When the engine torque is known, the load on the friction clutch  80 - 90  can be calculated based on the kinematics of the transmission  12  and the connection of the engine  14 . This allows a clutch load conversion to be determined that receives operating parameters such as the fuel flow rate and the engine output shaft speed, and outputs a clutch load. Depending on the implementation, the operating parameter conversions can be integrated into the surrogate model, or may be standalone modules that are executed prior to the surrogate model and have their output operating parameters input to the surrogate model when performing clutch monitoring and control. 
     After any operating parameter conversions are determined at the block  218 , control may pass to a block  220  to determine whether there are other friction clutches  80 - 90  for which a surrogate model must be generated. Friction clutches  80 - 90  with different physical configurations may generate heat differently and therefore require unique FEA models and surrogate models. Also, friction clutches  80 - 90  with the same physical configuration may be subjected to different sets of operating conditions by the components connected thereto. For example, the friction clutches  86 ,  88  may have the same physical configurations, but may be subjected to different clutch loads from the coupling  76  versus the planet carrier  54 , respectively. In this case, the surrogate model for the friction clutch  86  may not provide accurate local peak temperatures for the friction clutch  88 . In these situations, control may pass from the block  220  back to the block  202  to execute the surrogate model generation routine  200  for each friction clutch  80 - 90  requiring a unique surrogate model. After all the surrogate models are generated for all friction clutches  80 - 90 , the routine  200  may terminate. 
     After being generated by the routine  200 , the surrogate models may be loaded into the memory  144  of the ECM  140  for use in friction clutch monitoring and control during operation of the machine  10 .  FIG. 7  illustrates a flow diagram for an exemplary local peak temperature prediction and clutch control routine  230  utilizing the surrogate model for the corresponding friction clutch  80 - 90 . The routine  230  may be executed in parallel for each of the friction clutches  80 - 90  having a unique surrogate model, or having the same surrogate model but different operating parameter values at a given time due to differences in engagement and disengagement in the various transmission gears, differences in loading from the components to which the friction clutches  80 - 90  are connected, and other factors. For purposes of discussion, the routine  230  will be described with reference to prediction and control of one of the friction clutches  80 - 90 . 
     The routine  230  may begin at a block  232  where the transmission  12  is engaged due to manual input from an operator of the machine  10  or automatically by commands from the transmission control module of the ECM  140 . The manual or automatic input can cause the ECM  140  to transmit clutch control currents to one or more of the clutch control valves  120 - 130  to engage the corresponding friction clutches  80 - 90  and shift the transmission  12  to one of the gears according to the truth table  92 . For example, the ECM  140  may transmit control signals to the clutch control valves  120 ,  126 ,  130  to engage the friction clutches  80 ,  86 ,  90 , respectively, to shift into the first forward gear  1 F. 
     After the transmission  12  is engaged at the block  232 , control passes to a block  234  where the machine operating parameters are detected and collected by the ECM  140 . The machine operating parameters can include various operating parameters that can be used to determine the local peak temperatures in the friction clutch  80 - 90  as discussed above. The clutch control current transmitted to the clutch control valves  120 - 130  of the friction clutch  80 - 90  being monitored may be provided by the transmission control module being executed by the ECM  140 . The transmission shaft speeds may be provided to the ECM  140  by the transmission speed sensors  152 ,  154 , and/or the engine output shaft speed from the engine output speed sensor  156  may be forwarded by the engine ECM  150 . Machine operating parameter used to determine the clutch load, such as the fuel flow rate for the engine  14  discussed above, may be provided from the engine governor control module at the engine ECM  150 . Additional operating parameters relevant to local peak temperature prediction and clutch control may be determined and collected in similar manners. 
     As the machine control parameters are collected at the block  234 , control may pass to a block  236  where any necessary calculations are performed to convert collected machine operating parameters to input parameters for the surrogate model of the friction clutch  80 - 90 . Such calculations or conversions may be necessary where operating parameter conversions have been generated at the block  218  as discussed above. Consequently, the clutch control current value to the clutch control valve  120 ,  130  may be converted to a clutch pressure value, and the fuel flow rate and engine output shaft speed may be converted to an engine torque or a clutch load. Additional or alternative conversions may be performed. In alternative embodiments, where the conversions are integrated into the surrogate model of the friction clutch  80 - 90 , the block  236  may be omitted as the collected machine operating parameters may be input directly to the surrogate model. 
     With the machine operating parameters collected at the block  234  and any necessary parameter conversions are performed at the block  236 , control may pass to a block  238  where the surrogate model input parameters are input to the surrogate model to determine the local peak temperature of the friction clutch  80 - 90  at the current operating conditions. As discussed above, the surrogate model was developed from the FEA simulation data to determine the local peak temperature without executing the calculations necessary in an FEA model simulation. Therefore, the surrogate model does not require an undue amount of processing resources of the ECM  140 . After executing the surrogate model with the current machine operating parameters at the block  238 , control may pass to a block  240  where local peak temperature data output by the surrogate model is transmitted to a machine monitoring location that may be remote from the machine  10 . In addition to addressing the current conditions and controlling the friction clutch  80 - 90  in real time, long-term tracking of the conditions to which the friction clutch  80 - 90  is subjected may be necessary to predict and schedule maintenance and replacement of the friction clutch  80 - 90 . Proactive clutch maintenance and replacement are discussed further below. 
     In addition to transmitting data to the machine monitoring location at the block  240 , control may pass to a block  242  where the local peak temperature of the friction clutch  80 - 90  is compared to a predetermined critical peak temperature. The critical peak temperature may be a temperature above which performance of the friction clutch  80 - 90  may degrade and a risk of excessive wear or other damage to the components of the friction clutch  80 - 90  may exist. If the local peak temperature output by the surrogate model is less than the critical peak temperature, then the friction clutch  80 - 90  is within the safe operating range and may continue to be engaged. Control may pass back to the block  234  to continue monitoring the machine operating parameters and the local peak temperature. 
     If the local peak temperature is greater than the critical peak temperature at the block  242 , the friction clutch  80 - 90  should be disengaged to prevent further heat generation until the friction clutch  80 - 90  can cool down. However, the machine  10  is still being driven by the engine  14  and the engaged transmission  12 . Therefore, it may be desirable for the disengagement of the friction clutch  80 - 90  to have minimal effect on the propulsion of the machine  10 . Consequently, control may pass to a block  244  where the ECM  140  may determine an alternative gear to which the transmission  12  should shift where the friction clutch  80 - 90  is disengaged that minimizes the effect of the gear shift on the machine  10 . As an example, the transmission  12  may be in the fourth foreword gear  4 F as shown in the truth table  92  with friction clutches  80 ,  84 ,  88  engaged. When the local peak temperature for the friction clutch  84  is greater than the critical peak temperature, it may be preferable to shift the transmission  12  to the third forward gear  3 F where the friction clutch  84  is disengaged instead of the fifth forward gear  5 F where the friction clutch  84  is still engaged or the sixth forward gear  6 F where the friction clutch is disengaged but the speed-to-torque ratio may be significantly different. In downshifting to the third forward gear  3 F, the friction clutch  86  must be engaged while the friction clutches  80 ,  88  remain engaged. The strategy for shifting in response to exceeding the critical peak temperature may be predetermined and based solely on the friction clutch  80 - 90  that exceeds the critical peak temperature and the current gear, or may incorporate dynamic determination of the gear to which the transmission will be shifted that takes into account factors such as shaft speeds, engine torque and the like that will influence the reaction of the machine  10  to the gear shift. 
     After the alternate gear is determined, control passes to a block  246  where the transmission control module of the ECM  140  disengages the overheating friction clutch  80 - 90  and shifts the transmission  12  to the alternate gear. In the above example, the transmission control module would cut off the clutch control current to the clutch control valve  124  of the friction clutch  84 , and transmit clutch control current to the clutch control valve  126  of the friction clutch  86  to engage the friction clutch  86  and downshift the transmission  12  from the fourth foreword gear  4 F to the third forward gear  3 F. 
     After the friction clutch  80 - 90  is disengaged and the transmission  12  is shifted at the block  246 , control may pass to a block  248  to determine whether the ECM  140  is still receiving commands to engage the transmission  12 . If the transmission  12  is to remain engaged, control may pass back to the block  234  to continue detecting and collecting machine operating parameter values and evaluating the local peak temperature of the friction clutch  80 - 90 . If the transmission  12  is disengaged at the block  248 , the routine  230  may cease execution until the transmission  12  is reengaged. 
     As discussed above, the local peak temperatures for the friction clutch  80 - 90  and associated machine operating parameter data may be transmitted to a machine monitoring location for accumulation and analysis.  FIG. 8  illustrates one embodiment of a proactive clutch maintenance routine  260  that utilizes the transmitted local peak temperature data to determine when the friction clutch  80 - 90  should be maintained or replaced. The routine  260  may begin at a block  262  where the local peak temperature and machine operating parameter data are received at the machine monitoring location. The machine monitoring location may be a field office at a worksite with responsibility for the machine  10  at the worksite, or a central office that has responsibility for monitoring machines  10  operating at multiple worksites. 
     After the data is received at the block  262 , control may pass to a block  264  where the local peak temperature and machine operating parameters are stored in a database along with previously received data for the friction clutch  80 - 90 . The stored data provides a historical record of the operation of the friction clutch  80 - 90  and the amount and severity of the usage to which it has been subjected since being placed into service. 
     In addition to storing the local peak temperature data in the database, control may pass to a block  266  where the data is input into a clutch data analytics module. The clutch data analytics module may use the current local peak temperature data along with historical data from the database to assess the present condition of the friction clutch  80 - 90 . The clutch data analytics module may be programmed to utilize information such as the service time since the transmission  12  was put into service, total operating hours where the transmission  12  has been engaged to drive the machine  10 , shaft speeds, loads, peak temperatures and other data influencing the wear and tear on the friction clutch  80 - 90  to determine whether the cumulative usage of the friction clutch  80 - 90  has reached a limit where preventive maintenance should be scheduled. Historical data and experience with previous friction clutches may serve as a basis for weighting the various factors for their influence on the useful life of the friction clutches  80 - 90 , and inputting the weighting into the configuration of the clutch data analytics module. 
     The output of the clutch data analytics module is evaluated at a block  268 . If the data indicates that the friction clutch  80 - 90  is not ready for maintenance, control may pass back to the block  262  to await subsequent transmissions of local peak temperature data. If the friction clutch  80 - 90  has reached the point in its useful life where preventive maintenance should be performed, control may pass to a block  270  where preventive maintenance on the friction clutch  80 - 90  is scheduled. The machine monitoring location may have a maintenance scheduling routine plan for the appropriate time and location for maintenance. The maintenance schedule routine may utilize information such as maintenance personnel availability, maintenance location availability, parts availability and order lead time, usage schedule for the machine  10  and other logistical information to determine an optimal time it to take the machine  10  out of service for maintenance on the friction clutch  80 - 90 . The maintenance schedule routine may also transmit notices to the machine operators, maintenance staff, facilities schedulers and others that you plan for the scheduled maintenance. After the maintenance is scheduled by the maintenance scheduling routine at the block  270 , control may pass back to the block  262  to await subsequent transmissions of local peak temperature data. 
     Determination and use of the local peak temperatures of the friction clutches  80 - 90  in monitoring and controlling the clutches  80 - 90  in the transmission  14  as disclosed herein can improve the ability to predict clutch durability and performance both in real time and over the long term. In real time, knowing the local peak temperatures at hot spot locations can provide more accurate identification of impending failure of the friction clutches  80 - 90  and the ability to take remedial steps before failure occurs than is possible when using an average temperature distribution. Dangerous conditions can be overlooked when only the average temperature is being evaluated. In other situations, uncertainty through the use of average temperatures may result in falsely identifying dangerous conditions by setting a threshold average temperature very low to ensure that all potentially dangerous conditions are covered even when the local peak temperatures are not close to being critical. The increased precision offered by evaluating local peak temperatures correspondingly increases the precision in identifying dangerous conditions and minimizing corrective actions to only those situations that truly require disengagement of the friction clutches  80 - 90 . Similar improvements may be realized over the long term where knowledge of the local peak temperatures can yield more accurate assessment of long term wear and tear on the friction clutches  80 - 90  and prediction of the approach of the ends of the useful lives of the friction clutches  80 - 90 . 
     While the preceding text sets forth a detailed description of numerous different embodiments, it should be understood that the legal scope of protection is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims defining the scope of protection. 
     It should also be understood that, unless a term was expressly defined herein, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to herein in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term be limited, by implication or otherwise, to that single meaning.