# Patent

## Title
Method for determining initial temperatures in dry dual clutch transmissions

## Abstract

A method for determining initial or starting temperatures for a dry dual clutch mechanism at vehicle start-up includes as determining a time lapse from shut-down to start-up. The method determines a housing air start temperature of the housing air within a bell housing case of the dry dual clutch mechanism at vehicle start-up, reads a first clutch stop temperature of a first clutch at vehicle shut-down, reads a housing air stop temperature of the housing air at vehicle shut-down, and determines a heat transfer coefficient between the first clutch and the housing air. The method includes determining a first clutch start temperature from, at least: the heat transfer coefficient between the first clutch and the housing air; a temperature differential between the first clutch stop temperature and the housing air stop temperature; and the housing air start temperature.

## Background
TECHNICAL FIELD
This disclosure relates to thermal modeling to determine clutch temperatures in dry dual clutch transmissions.
BACKGROUND
Motorized vehicles use dual clutch transmissions to combine some of the features of both manual and automatic transmissions. Dual clutch transmissions use two clutches to shift between sets of gears within the same transmission, operating with some of the characteristics of both manual and conventional automatic transmissions. Some dual clutch transmissions use oil-bathed wet multi-plate clutches, and some use dry clutches without oil or fluid.
SUMMARY
A method for determining initial or starting temperatures for a dry dual clutch mechanism at vehicle start-up is provided. The method includes one or more steps, such as determining a time lapse from a vehicle shut-down to the vehicle start-up. The method determines a housing air start temperature of the housing air within a bell housing case of the dry dual clutch mechanism at vehicle start-up, reads a first clutch stop temperature of a first clutch at vehicle shut-down, and reads a housing air stop temperature of the housing air at vehicle shut-down.
The method determines a heat transfer coefficient between the first clutch and the housing air. The method includes determining a first clutch start temperature from, at least: the heat transfer coefficient between the first clutch and the housing air; a temperature differential between the first clutch stop temperature and the housing air stop temperature; and the housing air start temperature. The method also includes executing a control action with the determined first clutch start temperature.
The above features and advantages, and other features and advantages, of the present invention are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the invention, as defined in the appended claims, when taken in connection with the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic plane intersection view of a powertrain having an illustrative dry dual clutch transmission usable with thermal models described herein;
FIG. 2 is a schematic flow chart of a method or algorithm for determining clutch temperatures in a dry dual clutch transmission, such as that shown in FIG. 1;
FIG. 3 shows schematic charts or graphs that broadly illustrate testing and validation of a thermal models applied to the dry dual clutch transmission shown in FIG. 1;
FIG. 4 shows a schematic chart or graph that broadly illustrates the initial temperature model; and
FIG. 5 is a schematic flow chart diagram of an algorithm or method for determining initial (or starting) temperatures in a dry dual clutch transmission, such as that shown in FIG. 1.



DETAILED DESCRIPTION
Referring to the drawings, wherein like reference numbers correspond to like or similar components whenever possible throughout the several figures, there is shown in FIG. 1 a schematic diagram of a powertrain 100. The powertrain 100 may be incorporated into a hybrid vehicle (not shown) or a conventional vehicle (not shown). Features, components, or methods shown or described in other figures may be incorporated and used with those shown in FIG. 1.
While the present invention is described in detail with respect to automotive applications, those skilled in the art will recognize the broader applicability of the invention. Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” et cetera, are used descriptively of the figures, and do not represent limitations on the scope of the invention, as defined by the appended claims.
The powertrain 100 includes a dry dual clutch transmission 110, which may be referred to herein as the dry DCT 110 and receives power from an internal combustion engine 112. The dry DCT 110 includes a transmission gearbox 114 and dual clutch mechanism 116. The engine 112 is drivingly connected for powerflow communication with the dry DCT 110. The dual clutch mechanism 116 selectively allows torque transfer between the engine 112 and the gearbox 114.
The gearbox 114 is operatively connected to a final drive 118 (or driveline). The final drive 118 is shown schematically and may include a front or rear differential, or other torque-transmitting mechanism, which eventually provides torque output to one or more wheels (not shown). The final drive 118 may include any known configuration, including front-wheel drive (FWD), rear-wheel drive (RWD), four-wheel drive (4WD), or all-wheel drive (AWD), without altering the description herein.
Only a portion of the powertrain 100 is illustrated in FIG. 1. The lower half (as viewed in FIG. 1) of the powertrain 100 is below a central axis 120, but may be substantially similar to the portions shown. The transfer shafts between the dual clutch mechanism 116 and the engine 112 and gearbox 114 are not shown in FIG. 1. The dual clutch mechanism 116 is housed in a bell housing or bell housing case 122.
The dual clutch mechanism 116 includes a first clutch 132 or clutch one (C1) and a second clutch 134 or clutch two (C2). A center plate 136 (CP) is between the first clutch 132 and the second clutch 134. Each of the first clutch 132 and the second clutch 134 includes friction discs, friction plates, or other friction materials. The center plate 136 contains corresponding friction plates.
A first friction interface 142 is disposed or occurs at the friction plates between the first clutch 132 and the center plate 136. When the dual clutch mechanism 116 is allowing slip (relative difference in rotational speed) and transferring torque between the first clutch 132 and the center plate 136, the first friction interface 142 generates heat. A second friction interface 144 occurs at the friction plates between the second clutch 134 and the center plate 136. When the dual clutch mechanism 116 is allowing slip and transferring torque between the second clutch 134 and the center plate 136, the second friction interface 144 generates heat.
A first pull cover 146 and a second pull cover 148 (PC1 and PC2, respectively) are operatively connected to other components of the dual clutch mechanism 116 and are configured to selectively apply or engage the first clutch 132 and the second clutch 134. The first pull cover 146 and the second pull cover 148 are used to actuate torque transfer of the first clutch 132 and the second clutch 134 order to selectively control power transfer to the gearbox 114. Some connections between components occur via, for example, bolts or fasteners and some connections are made with straps. The conduction properties of the different connection between components are altered by the type of materials connecting the components and by the area of conduction.
The designation of any specific element or component as “first” or “second” is illustrative and descriptive only. The numerical designations are not intended to be limiting and no requirement of connection should be implied from components having the same numerical designation.
The dry DCT 110, and the dual clutch mechanism 116, may be controlled and monitored by a controller or control system (not shown). The control system may include one or more components with a storage medium and a suitable amount of programmable memory, which are capable of storing and executing one or more algorithms or methods to effect control of the dry DCT 110 or the powertrain 100. Each component of the control system may include distributed controller architecture, such as a microprocessor-based electronic control unit (ECU). Additional modules or processors may be present within the control system. The control system may alternatively be referred to as a transmission control processor (TCM).
The interior chamber of the bell housing case 122 is filled with housing air 150. Depending upon the configuration of the dual clutch mechanism 116 and the thermal model applied used to determine temperatures of the dual clutch mechanism 116, the powertrain 100 may include a housing air temperature sensor 152.
The housing air temperature sensor 152 measures the temperature of air within the bell housing case 122. The powertrain may also include an ambient air temperature sensor 154, an engine coolant temperature sensor 156, and a gearbox oil sensor 158. As used herein, ambient air refers to the air just outside of the bell housing case 122. The sensors may also be measuring or sensing other data. The temperature measurements from these sensors may be used in thermal models to determine the temperatures of the components of the dual clutch mechanism 116.
In the dual clutch mechanism 116, there is a critical temperature of the friction surfaces that carry torque for the first clutch 132 and the second clutch 134. Above this temperature, the components may start to suffer permanent damage. Furthermore, the clutch friction characteristics—i.e., the coefficient of friction and the torque carrying capacity of the first clutch 132 and the second clutch 134—are a function of the temperatures of the first friction interface 142 and the second friction interface 144.
In many configurations of the dry DCT 110, it may be difficult to place a temperature sensor directly on the first clutch 132 and the second clutch 134, and may be impossible to place a temperature sensor near the first friction interface 142 and the second friction interface 144 of the dual clutch mechanism 116. Therefore, the control system uses a thermal model to determine the temperatures of the first clutch 132 and the second clutch 134, to estimate the torque capacity at the first friction interface 142 and the second friction interface 144, and also to provide driver warnings to prevent misuse of the dry DCT 110.
A seven-state thermal model may be used to determine the temperatures of the first clutch 132 and the second clutch 134 for the dry DCT 110. However, in some configurations, a simplified, five-state thermal model may be used instead. The five-state thermal model requires less computational throughput.
When the seven-state thermal model is used, the states (or temperatures) are calculated at: the first clutch 132, the second clutch 134, the center plate 136, the first pull cover 146, the second pull cover 148, the bell housing case 122, and the housing air 150. When the simplified, five-state thermal model is used, the states are reduced to: the first clutch 132, the second clutch 134, the center plate 136, the first pull cover 146, and the second pull cover 148. The five-state thermal model may be used when the temperature of the housing air 150 is known, such as from the inclusion of the housing air temperature sensor 152.
The five-state thermal model will be described first. When either the first clutch 132 or the second clutch 134 is applied, the apply force pushes the corresponding pressure plate of the first clutch 132 or the second clutch 134, squeezing the friction discs against the center plate 136. The dual clutch mechanism 116 is encased in the bell housing case 122, which is assembled between the engine 112 and the gearbox 114. The first clutch 132, the second clutch 134, the center plate 136, the first pull cover 146, and the second pull cover 148 are all masses that conduct heat, and each mass in the system is represented by a single temperature state.
The bell housing case 122 shown in FIG. 1 has no forced cooling and has no vents. However, the models described herein may be changed to incorporate cases with different cooling and airflow The heat from the masses is transferred by convection to the housing air 150 and from the housing air 150 to the mass of the bell housing case 122. Heat is then convected from the bell housing case 122 to the ambient air just outside of the bell housing case 122.
There is also heat transfer between the bell housing case 122, the engine 112 and the gearbox 114. However, it is assumed that heat from the masses is transferred only to bell housing air 150. Therefore, when the housing air temperature sensor 152 provides known temperature of the housing air 150, the five-state thermal model is configured to use state equations representing the temperature of the masses. The five-state thermal model also assumes that other heat sources, such as the engine 112, the gearbox 114, and the ambient air, will not separately affect the temperature prediction beyond the measured temperature of the housing air 150.
The governing equation describing the heat balance for each individual mass is given by:

Massi*Cpi*dTi=Qi—in−Qi—out 

where Massi and Cpi represent the mass and specific heat of the specific component of the dual clutch mechanism 116 under consideration; Qi—in and Qi—out represent the heat input and heat output for the mass, respectively; and dTi is the change in mass temperature with respect to time. All equations described herein are illustrative only and may be modified based upon specific configurations of the powertrain 100, the dry DCT 110, and the dual clutch mechanism 116.

When either the first clutch 132 or the second clutch 134 is applied and torque is transmitted across the clutch, heat is generated at the first friction interface 142 or the second friction interface 144 if the applied clutch is slipping. When there is no slip, the two sides of the clutch are rotating substantially in sync and substantially all power is transferred through the clutch.
Using the first clutch 132 for illustration, the five-state thermal model assumes that the heat generated at first friction interface 142 is absorbed by substantially equally by the first clutch 132 and center plate 136. The temperatures of the first clutch 132 and center plate 136 increase during the slip event, resulting in heat transfer due to conduction and convection to other components in the dual clutch mechanism 116.
Because the equations are similar for all of the masses used in the five-state and the seven-state thermal models, only the equations for the first clutch 132 are illustrated here. The heat power input (Watts) to the first clutch 132 is the product of torque (Nm) and slip speed (rad/s) at the first clutch 132. The heat power integrated over time results in heat (joules).
The slip speed is known or may be determined from measurements or estimates of input speeds and output speeds of the dual clutch mechanism 116 or the dry DCT 110. Similarly, the torque carried by the first clutch 132 is known or determined from torque of the engine 112 or other parameters.
The discrete form of the heating mode of the first clutch 132 is given by:

Thc1(k+1)=Tc1(k)+(1⁄2Torquec1*ωC1—Slip*delta_time)/(Cpc1*Massc1)

where Cpc1 is the specific heat of the material of the first clutch 132 and Massc1 is the mass of the first clutch 132. The term k represents the current time at which the variable (such as temperature of the first clutch 132) is computed or represented and is the instant (or current) time period or loop of the thermal model. The term k+1 represents the next time period, after the lapse of delta_time.

The heat losses due to conduction from the first clutch 132 to the first pulling cover 146 and to the center plate 136 are given by the following expressions:

Heatloss—PC1=[Tc1(k)−Tpc1(k)]*Cond*Area—PC1

Heatloss—CP=[Tc1(k)−Tcp(k)]*Cond*Area—CP 

where Cond is the thermal conductivity of the connecting material. Area_PC1 and Area_CP are the conducting areas divided by the thickness of the conducting sections. The area/thickness values for each conduction path may be identified by testing and data optimization or by CAD models. These heat losses are subtracted from the heat input due to the slippage at the first friction interface 142.

The cooling of the first clutch 132 due to convection is given by:

Tcc1(k+1)=(Tc1(k)−Thousing(k))*exp(−b*delta_time)+Thousing(k)

where Thousing is the measured housing air temperature and b is the cooling coefficient for the first clutch 132.

The cooling coefficient is given by:

b=hc1*Ac1/(Cpc1*Massc1)

where Ac1 is the surface area of the first clutch 132 that is convecting the heat and hc1 is the heat transfer coefficient.

The heat transfer coefficient is calculated using the Nusselt number. The Nusselt number is proportional to the square root of the Reynold's number, with the proportionality constant, NuReConstc1, to be determined from the cooling data for the first clutch 132. The Reynolds number is function of clutch speed, as shown in the equations below:

hc1=Nu*Kair/mean_radius

Nu=NuReConstc1*sqrt(Re)

Re=ωc1*mean_radius2/(mu/rho)

where mu is the viscosity of air, rho is the density of air, Kair is the conductivity in air, and the mean_radius is of the first clutch 132. Similar equations can be derived for the other four masses (the second clutch 134, the center plate 136, the first pull cover 146, and the second pull cover 148) in the dual clutch mechanism 116.

With similar equations for all five of the masses in the dual clutch mechanism 116, the control system determines the operating temperature of any of the individual components due to heating during slip events (usually from gear changes or launches) and cooling during non-slip events (steady state operations). The goal, or target, of the five-state thermal model is to determine the temperature of the first clutch 132 and the second clutch 134. These temperatures may be referred to as the bulk temperatures of the first clutch 132 and the second clutch 134 and represent average temperature throughout the whole mass of the component. From the bulk temperatures, the control system can determine whether the first clutch 132 and the second clutch 134 are below critical temperatures and estimate the torque capacity at the first friction interface 142 and the second friction interface 144.
Some of the inputs and values of the heating and cooling equations may not be easily determined through inspection, reference tables, or CAD models. These inputs and values may be determined through data optimization by comparing testing data of the dual clutch mechanism 116 with pre-optimized simulations. The data is optimized by comparing the simulations with the test data, and the five-state thermal model is developed with more-precise inputs and values for the actual dual clutch mechanism 116 used.
The five-state thermal model is developed to determine temperatures of the first clutch 132 and the second clutch 134 based upon heating events (clutch slipping) and cooling events (periods of non-slipping engagement or non-engagement). The five-state thermal model may be running within the control system at all times, including during vehicle off periods. In such a case, the five-state thermal model tracks all changes to the temperature of the first clutch 132 and the second clutch 134, and the temperatures are accurate absolute temperatures.
However, if the five-state thermal model is not running while the vehicle is turned off or in shut-down mode, the five-state thermal model will actually be determining the changes to temperatures of the first clutch 132 and the second clutch 134. Therefore, the control system may also need to know the initial (starting) temperatures of the first clutch 132 and the second clutch 134 at vehicle start-up in order to determine the absolute temperatures from the temperature changes (delta temperature) determined by the five-state thermal model. Vehicle start-up and vehicle shut-down states may be defined in numerous ways or may be based upon the running state of the engine 112. The initial temperatures may be separately determined by the control system—such as from another model.
The five-state thermal model operates with known temperatures from the housing air 150, such as from the housing air temperature sensor 152. However, it may not always be practical or possible to have the housing air temperature sensor 152 or another mechanism for determining the temperature of the housing air 150. Without known housing air 150 temperatures, the five-state thermal model may be insufficient to determine the temperature of the first clutch 132 and the second clutch 134. Therefore, the non-simplified model, the seven-state thermal model, is used to determine the temperature of the first clutch 132 and the second clutch 134 when the temperature of the housing air 150 is not known or readily determined. Additional temperature states may be incorporated into the five-state and seven-state thermal models illustrated in detail herein.
The seven-state thermal model includes temperature states or nodes for the bell housing case 122 and for the housing air 150 contained therein. The five-state thermal model included only two heat sources, the heat generated during slip events at the first friction interface 142 and the second friction interface 144 of the first clutch 132 and the second clutch 134, respectively. However, the dual clutch mechanism 116 is also in heat-exchange communication with the engine 112, the gearbox 114, and the ambient air outside of the bell housing case 122. The effects of these other heating or cooling sources are actually incorporated into the five-state thermal model through the known temperature of the housing air 150. Since the seven-state thermal model does not include known temperatures of the housing air 150, the heat effects of the engine 112, the gearbox 114, and the ambient air are incorporated into the seven-state thermal model.
When the seven-state thermal model is used, the powertrain 100 is equipped with mechanisms to determine the temperature of the engine 112, the gearbox 114, and the ambient air outside of the bell housing case 122. As illustrated in FIG. 1, the engine coolant temperature sensor 156, the gearbox oil sensor 158, and the ambient air temperature sensor 154 may determine these temperatures for used in the seven-state thermal model. Alternatively, especially for the ambient temperature, other sensors may be used to closely approximate the temperature. For example, a sensor may be located at the air intake for the engine 112, and this temperature may be used as the ambient air temperature for the seven-state thermal model, instead of locating the ambient air temperature sensor 154 just outside of the bell housing case 122.
The two additional temperature states and the three additional heating and cooling sources are replacements in the seven-state thermal model for the known temperature of the housing air 150 in the five-state thermal model. Therefore, the five-state thermal model is a simplified version of the seven-state thermal model. The seven-state thermal model includes only conduction heat transfer with the engine 112 and the gearbox 114, with convention and radiation from those sources assumed to be negligible.
The equations for the housing air 150 temperature and bell housing case 122 case temperature can be written as follows. For the housing air 150:

Massh*Cph*dTh=Qh—in−Qh—out 

where subscript h refers to housing air 150 and dTh is the change in air temperature with respect to time. Qh—in is the amount of heat convected from the five masses in the dual clutch mechanism 116. The expressions for Qh—in was given in the description of the five-state thermal model. Qh—out is the amount of heat convected to the bell housing case 122 and is given by:

Qh—out=hair*Areaair(Th(k)−Tc(k))

where hair and Areaair are heat transfer coefficient and area of convection and these are determined by the parameter optimization.

Similarly, for the bell housing case 122:

Massc*Cpc*dTc=Qc—in−Qc—out 

where subscript c refers to bell housing case and dTc is the change in temperature of the bell housing case 122 with respect to time. Qc—in is the amount of heat convected from housing air 150 (Qh-out, given above) and the heat conducted from the engine 112 and gearbox 114 sides.

Focusing only on the conduction from engine 112 and gearbox 114 to the bell housing case 122, we can write:

Qeng—gear=Kc*Areaeng(Teng(k)−Tc(k))+Kc*Areagear(Tgear(k)−Tc(k))

where Teng is the temperature of the coolant in engine 122, as measured by engine coolant temperature sensor 156, and Tgear is the temperature of oil in the gearbox 114, and measured by gearbox oil sensor 158. The areas of conduction, Areaeng and Areagear, may be very complex due to the odd shapes and interfaces of the components. Therefore the areas of conduction may be determined for any specific powertrain 100 by the parameter optimization from test data.

The value Qc—out is the amount of heat conducted to the ambient air just outside of the bell housing case 122, and is given by:

Qc—out=Kc*Areac(Tc(k)−Tamb(k))

where Area is the area of convection of the bell housing case 122 and may also be determined by the parameter optimization. Tamb(k) is the ambient temperature around the bell housing case 122. This temperature might be different from the temperature outside the vehicle. The intake air temperature of the engine 112 may be substituted for the ambient temperature.

Therefore, the convention and conduction for each of the seven components in the seven-state thermal model can be determined. The seven-state thermal model is developed with a lumped parameter approach, where each component is represented by one temperature state. After implementation for the specific vehicle and powertrain 100, the control system uses the seven-state thermal model to determine the bulk temperatures of the first clutch 132 and the second clutch 134.
The seven-state thermal model may not be running while the vehicle is turned off or in shut-down mode, such that the seven-state thermal model is actually determining the changes to temperatures—as opposed to the absolute temperatures—of the first clutch 132 and the second clutch 134. Therefore, the control system may also need to know the initial (starting) temperatures of the first clutch 132 and the second clutch 134 at vehicle start-up in order to determine the absolute temperatures from the temperature changes (delta temperature) determined by the seven-state thermal model.
Referring now to FIG. 2, and with continued reference to FIG. 1, there is shown a schematic flow chart diagram of an algorithm or method 200 for determining clutch temperatures in a dry dual clutch transmission, such as the dry DCT 110 shown in FIG. 1. FIG. 2 shows only a high-level diagram of the method 200. The exact order of the steps of the algorithm or method 200 shown in FIG. 2 is not required. Steps may be reordered, steps may be omitted, and additional steps may be included. Furthermore, the method 200 may be a portion or sub-routine of another algorithm or method.
For illustrative purposes, the method 200 may be described with reference to the elements and components shown and described in relation to FIG. 1 and may be executed by the control system. However, other components may be used to practice the method 200 and the invention defined in the appended claims. Any of the steps may be executed by multiple components within the control system.
Step 208: Start.
The method 200 may begin at a start or initialization step, during which time the method 200 is monitoring operating conditions of the vehicle and of the powertrain 100. Initiation may occur, for example, in response to the vehicle operator inserting the ignition key or in response to other specific conditions being met. The method 200 may be running constantly or looping iteratively whenever the vehicle is in use.
Step 210: Initial Loop?
The method 200 determines whether it is running on an initial or starting loop after the vehicle has been turned on. If this is the initial loop, the method 200 will determine initial temperatures to be used in the five-state or the seven-state thermal model. To determine the initial temperatures, the method 200 proceeds through a sub-process 400, which uses an initial temperature model (described herein) to calculate or determine the needed initial temperatures.
Step 212: Read Previous States (Temperatures).
The method 200 reads the previous five or seven temperature states. The previous states are stored by the control system from the last loop of the method 200. If the method 200 is running for the first time, such as after the engine 112 has just started, the previous states may be replaced by initial conditions of the components. If needed, the initial conditions may be either calculated or estimated by the control system.
Step 214: Determine Heat from Clutches.
The method 200 determines the heat being generated by the clutches. The heat generated is a function of torque capacity and slip speed of the first clutch 132 and the second clutch 134. The heat is generated at the first friction interface 142 and the second friction interface 144.
When neither the first clutch 132 nor the second clutch 134 is slipping, such as during steady state operation, no heat is generated by the clutches. Generally, when no heat is generated by the clutches, the dual clutch mechanism 116 is cooling.
Step 216: Determine Housing Air Temperature.
The method 200 takes the temperature of the housing air 150 into account regardless of the thermal model being used. If the temperature of the housing air 150 is known, such as from the housing air temperature sensor 152, then the five-state thermal model may be used, and the method 200 simply takes the known temperature from the housing air temperature sensor 152. However, if the temperature of the housing air 150 is not known, then method 200 uses the seven-state thermal model instead of directly measuring the temperature of the housing air 150.
Step 218: Determine Ambient, Engine, and Gearbox Temperatures.
If the method 200 is using the seven-state thermal model, steps 218 and 220 are also executed. The method 200 determines or measures the temperatures of the ambient air outside of the bell housing case 122, the engine 112, and the gearbox 114. The ambient air temperature sensor 154, the engine coolant temperature sensor 156, and the gearbox oil sensor 158, respectively, may measure these temperatures. Alternatively, the temperatures may be derived or approximated from other known conditions.
Step 220: Determine Heat from Ambient, Engine, and Gearbox.
The method 200 calculates the heat transfer between the bell housing case 122 and the ambient air outside of the bell housing case 122, the engine 112, and the gearbox 114. Depending upon the relative temperatures involved, heat may be flowing into or out of the bell housing case 122.
Step 222: Load Model Parameters.
The method 200 loads the parameters of the dual clutch mechanism 116 for use with the five-state or seven-state thermal model. The parameters include, without limitation: heat transfer coefficients and other characteristics of the specific materials making up the components, Nusselt and Reynolds numbers for the components experiencing convection, and the areas and thickness of conduction interfaces between components.
Step 224: Apply Five-State or Seven-State Thermal Model.
The method 200 applies one of the thermal models. If the temperature of the housing air 150 is known, the method 200 applies the five-state thermal model and includes temperature states for: the first clutch 132, the second clutch 134, the center plate 136, the first pull cover 146, and the second pull cover 148. When the temperature of the housing air 150 is not known, the method 200 applies the seven-state thermal model and further includes temperature states for the bell housing case 122 and the housing air 150.
Step 226: Output Bulk Temperature of Clutches C1 and C2.
From the thermal model, the method 200 determines the temperatures of the first clutch 132 and the second clutch 134. These temperatures may be the primary goal of the method and of the five-state or seven-state thermal model.
The temperatures of the first clutch 132 and the second clutch 134 may be compared to the critical temperatures for the friction linings of the first clutch 132 and the second clutch 134 and to alert the driver of possible damaging conditions. Furthermore, the temperatures of the first clutch 132 and the second clutch 134 may be used to calculate the coefficient of friction of the first friction interface 142 and the second friction interface 144.
Step 228: Execute Control Action.
The method 200 executes a control action based upon, at least, the determined temperatures of the first clutch 132 and the second clutch 134. Executing the control action may include many tasks or operations.
For example, the control action may include storing all (five or seven) of the determined temperatures. The stored temperatures may be used during the next loop, or may be stored as the last conditions when the vehicle or the engine 112 is turned off.
Executing the control action may include determining the actual coefficient of friction at the first fiction interface 142 and the second friction interface 144 based upon the determined temperatures of the first clutch 132 and the second clutch 134. The control action may also include storing the temperatures for calculation of maintenance or service actions and timelines for the first clutch 132 and the second clutch 134 or other portions of the powertrain 100.
Step 230: Stop/Loop.
The method 200 may stop running until called to run again by the control system, such as due to occurrence of events likely to change the temperature of components of the dual clutch mechanisms 116. Alternatively, the method 200 may run with a scheduled number of loops per time segment, such as several times per second.
Referring now to FIG. 3, and with continued reference to FIGS. 1-2, there are shown schematic charts or graphs that broadly illustrate testing and validation of the thermal models described herein. FIG. 3 shows actual test data compared with actual data from one of the five-state thermal model and the seven-state thermal model (in the description of FIG. 3, both will be referred to generally as the “thermal model”). During the test, the first clutch 132 was used for repeated launches from 0 to 1200 rpm slip speed, and then allowed to cool.
In the test shown in FIG. 3, the temperatures of the first clutch 132, the second clutch 134, and the center plate 136 were actually measured. The results of the thermal model with optimized parameters where also calculated.
A chart 310 shows the temperature of the first clutch 132, with temperature shown on a y-axis 312 and time on an x-axis 314. A measured temperature of the first clutch 132 is shown as a solid line 320. The upward spikes in the line 320 are increases in temperature due to the heat created as the first clutch 132 slips from non-engagement to complete engagement during the launch events. A simulated temperature from the thermal model is shown as a dashed line 322.
A chart 330 shows the temperature of the second clutch 134, with temperature shown on a y-axis 332 and time on an x-axis 334. A measured temperature of the second clutch 134 is shown as a solid line 340. A simulated temperature of the second clutch 134 from the thermal model is shown as a dashed line 342.
A chart 350 shows the temperature of the center plate 136, with temperature shown on a y-axis 352 and time on an x-axis 354. A measured temperature of the center plate 136 is shown as a solid line 370. A simulated temperature of the center plate 136 from the thermal model is shown as a dashed line 372. The upward spikes in the solid line 370 are increases in temperature due to the heat created in the first clutch 132 and passed into the center plate 136 from the first friction interface 142.
As shown in FIG. 3, the thermal model closely predicts the temperatures of the first clutch 132 during the test shown. The thermal model also closely predicts the temperature of the second clutch 134 and the center plate 136.
The five-state and seven-state thermal models described herein generally determine temperatures of the first clutch 132 and the second clutch 134 (and other components) based upon the heating and cooling flows during operation of the vehicle. However, temperature changes, particularly cooling of the dual clutch mechanism, occur even while the vehicle is off. Therefore, unless the initial temperatures are known or calculated, the thermal models may be calculating the changes in temperature of the first clutch 132 and the second clutch 134 without having an accurate starting point. An initial temperature model or method for determining the initial temperature states of the dual clutch mechanism 116 is also described herein.
Like the seven-state thermal model, the initial temperature model may be simplified if the temperature of the housing air 150 is known from the housing air temperature sensor 152. If the temperature of the housing air 150 is unknown, the initial temperature model will first calculate the temperature of the housing air 150. Note that when the temperature of the housing air 150 is unknown, the control system will be using the results of the initial temperature model with the seven-state thermal model to determine the temperatures of the first clutch 132 and the second clutch 134 while the vehicle is running.
To compute the initial temperatures for components of the dual clutch mechanism 116, it is assumed that when the control system is powered down at vehicle shut-down, the last available states (temperatures) of the thermal model are stored. Also, the last available ambient temperature, and other temperatures, such as engine coolant and gearbox temperatures, may be stored. Furthermore, the control system is configured to determine the time lapse during for which the control system was off.
Note that when the dry DCT 110 is incorporated into a hybrid vehicle, the engine 112 may not be the only source of power for the dry DCT 110. Therefore, the on/off state of the engine 112 may not be the only indicator of whether the dry DCT 110 and the powertrain 100 are in use, and the control system may be operable even though the engine 112 is shut down (or un-fueled).
The equation for the temperature of the bell housing case 122 at restart of the vehicle can be written as:

Tc—start=(Tc—stop−Tamb—stop)*exp(−bc*time)+Tamb—start 

where subscript “c” refers to the bell housing case 122 and subscript “amb” refers to the ambient air. Tc—stop is taken form the seven-state thermal model, Tamb—stop measured by the ambient air sensor 152, and both temperatures stored when the engine 112 or the vehicle was shut down. Tamb—start is the measured ambient temperature when the vehicle is subsequently restarted after the time lapse. The temperature of the coolant in the engine 112 may also be used in the calculation of the starting temperature for the bell housing case 122.

The heat transfer coefficient, bc, for the bell housing case 112 may be determined from data optimization and is a function of the temperature difference between the bell housing case 122 and the ambient air; (Tc—stop−Tamb—stop). Optimization of the heat transfer coefficient may be determined by fitting a table lookup function to measured experimental data.
After the temperature of the bell housing case 122 is determined, the temperature of the housing air 150 is determined using the equation:

Th—start=(Th—stop−Tc—stop)*exp(−bh*time)+Tc—start 

where subscript “h” refers to the housing air 150 and “c” refers to the bell housing case 122. Th—stop and Tc—stop (from the seven-state thermal model) are temperatures stored at the last shut down and Tc—start is the estimated temperature of the bell housing case 112 from the equation above.

If the temperature of the housing air 150 is known from the housing air temperature sensor 152, such that the control system is using the five-state thermal model, the above portions of the initial temperature model may be skipped. Therefore, the initial temperature model used with the five-state model may be considered as a simplified version of the initial temperature model used for the seven-state thermal model.
The initial temperature model, unlike the five-state and seven-state thermal models, assumes that heat conduction among the first clutch 132, the second clutch 134, and the center plate 136 is negligible. Therefore, the initial temperature model assumes that the main heat transfer path is convection to the housing air 150. The cooling equations for the clutch masses—the first clutch 132, the second clutch 134, and the center plate 136—are decoupled, and the masses are considered separately.
The cooling equations are similar for the first clutch 132, the second clutch 134, and the center plate 136, so only the equation for the first clutch 132 is shown here. The heat transfer (cooling) can be described using a temperature difference exponential function for the temperature of the first clutch 132 at vehicle start-up (Tc1—start). The critical parameter is the cooling coefficient, bc1, for the first clutch 132, bc1, in the following:

Tc1—start=(Tc1—stop−Th—stop)*exp(−bc1*time)+Th—start 

where the cooling coefficient is bc1. The cooling coefficient is given by:

bc1=hc1Ac1/(Cpc1*Massc1)

where Ac1 is the surface area of the pressure plate of the first clutch 132 that is convecting the heat, and hc1 is the heat transfer coefficient between the first clutch 132 and the housing air 150.

The heat transfer coefficient, hc1, is a function of the temperature difference between first clutch 132 and the housing air 150, and can be obtained from a look up function, illustrated in the equation:

hc1=f(Tc1—stop−Th—stop)

where the lookup table is calibrated using a nonlinear optimization approach, comparing testing data and repeated simulations with the initial temperature model. The heat transfer coefficient is, therefore, treated by the initial temperature model as a function of the temperature difference between the stored temperature of the first clutch 132 and the stored temperature of the housing air 150.

Note that if the calculation of the initial temperature is done in one loop of the control system at vehicle start-up, then only one value of the heat transfer coefficient will be used, irrespective of the time lapse (vehicle-off duration). However, the time lapse can vary from minutes to hours. During long cooling periods (the vehicle-off times), the value of the heat transfer coefficient changes due to changes in the temperature differential between the first clutch 132 (or the other components) and the housing air 150.
In order to incorporate the changing heat transfer coefficients, the initial temperature model calculates the start temperature using multiple steps within one control loop at the vehicle restart. The number of steps or segments per time lapse may be optimized based upon the specific configuration of the powertrain 100. Alternatively, a fixed number of segments may be used, irrespective of the time lapse. For example, and without limitation, the initial temperature model may use a ten-segment calculation algorithm.
During the illustrative ten-segment calculation, the vehicle-off time lapse is divided into ten equal segments—such as six minutes each, if the time lapse was sixty minutes. The temperature of the housing air 150 is then linearly interpolated for these ten time points using Th—stop and Th—start. For each of the ten segments, the heat transfer coefficient equation is successively used by inputting the start temperature from one segment as a stop temperature for the next segment, such that the Th—start calculated for the third segment becomes the Th—stop used for the fourth segment.
To estimate the initial temperatures for the first pull cover 146 and the second pull cover 148, the initial temperature model uses different logic. The first pull cover 146 and the second pull cover 148 are bolted directly to the masses of the first clutch 132 and the second clutch 134.
After the vehicle is turned off, the temperatures of the first pull cover 146 and the second pull cover 148 may initially increase even though no additional heat is being created in the dual clutch mechanism 116. This temperature increase occurs if the first clutch 132 and the second clutch 134 are at a higher temperature. Therefore, the initial temperature model assumes that the temperatures of the first pull cover 146 and the second pull cover 148 will begin to eventually approach the temperatures of the first clutch 132 and the second clutch 134, respectively.
The initial temperature model uses a calibrated convergence time to allow the temperatures of first pull cover 146 and the second pull cover 148 to equal the temperatures of the first clutch 132 and the second clutch 134. After the convergence time, the temperature of the first pull cover 146 is assumed to be equal to the temperature of the first clutch 132, and the temperature of the second pull cover 148 is assumed to be equal to the temperature of the second clutch 134. Before the convergence time expires, the temperature of the first pull cover 146 linearly approaches the temperature of the first clutch 132, and the temperature of the second pull cover 148 linearly approaches the temperature of the second clutch 134.
Referring now to FIG. 4, and with continued reference to FIGS. 1-3, there are shown schematic charts or graphs that broadly illustrate the initial temperature model. FIG. 4 shows a chart 400 illustrating a time lapse (vehicle off) period of approximately sixty minutes, which may be the sub-process 400 identified in FIG. 2. The powertrain 100 illustrated in FIG. 1 includes the housing air temperature sensor 152, such that the temperature of the housing air 150 is known. The data determined from the initial temperature model illustrated in FIG. 4 may be fed into the five-state thermal model for use after the vehicle restarts.
The chart 400 shows initial temperature model determining the temperature of the first clutch 132 during the cooling period. Temperature (in degrees Celsius) is shown on a y-axis 412 and time (in minutes) on an x-axis 414. A measured temperature of the housing air 150 is shown as a solid line 420.
A temperature of the first clutch 132 determined by the initial temperature model is shown as a dashed line 422. A temperature of the first pull cover 146 determined by the initial temperature model is shown as a long-dashed line 424.
In the illustrative situation shown in FIG. 4, the initial temperature model breaks the time lapse of sixty minutes into ten segments 426 of six minutes each. At vehicle shut-down, the temperature of the first clutch 132 (Tc1—stop) was approximately 100 degrees, and the temperature of the housing air 150 (Th—stop) was approximately 50 degrees.
In applying the initial temperature model, the control system calculates the heat transfer coefficient between the first clutch 132 and the housing air 150 for each segment. That heat transfer coefficient is used to determine the start temperature of the first clutch 132 at the end of each segment, which then becomes the stop temperature of the first clutch 132 for the next segment. Therefore, the determined temperature of the first clutch 132 shown on dashed line 422 is a curve formed from ten linear segments. Eventually, the temperature of the first clutch 132 and the temperature of the housing air 150 will merge and equalize with the ambient air temperature.
The initial temperature model determines the temperature of the first pull cover 146 by applying a linear section during the convergence time until the temperature of the first pull cover 146 reaches the temperature of the first clutch 132. After the convergence time, approximately 15 minutes in this illustrative initial temperature model, the temperature of the first pull cover 146 is equal to the temperature of the first clutch 132. The control system may simply note that the time lapse was greater than the convergence time and set the temperature of the first pull cover 146 is equal to the temperature of the first clutch 132. Though not separately shown, the initial temperature model similarly determines the temperatures of the second clutch 134 and the second pull cover 148, and also the center plate 136.
Referring now to FIG. 5, and with continued reference to FIGS. 1-4, there is shown a schematic flow chart diagram of an algorithm or method 500 for determining initial (or starting) temperatures in a dry dual clutch transmission, such as the dry DCT 110 shown in FIG. 1. FIG. 5 may be a sub-process of the method 200 shown in FIG. 2. The exact order of the steps of the algorithm or method 500 shown in FIG. 5 is not required, and FIG. 5 shows only a high-level illustration of the method 500. Steps may be reordered, steps may be omitted, and additional steps may be included.
For illustrative purposes, the method 500 may be described with reference to the elements and components shown and described in relation to FIG. 1 and may be executed by the control system. However, other components may be used to practice the method 500 and the claimed subject matter. Any of the steps may be executed by multiple components within the control system.
Step 510: Start.
The method 500 may begin at a start or initialization step, during which time the method 500 is monitoring operating conditions of the vehicle and of the powertrain 100. Initiation may occur, for example, in response to the vehicle operator inserting the ignition key or in response to other specific conditions being met, or in response to being called-up as a sub-process of the method 200. The method 500 may be configured to run on only a single loop or to run multiple times to validate its results.
Step 512: Read/Load Stop Temperatures.
The method 500 reads or loads (from the control system memory) the stop temperatures, which were stored from the last operating states at vehicle shut down. The stop temperatures read include, without limitation: the first clutch 132, the second clutch 134, the center plate 136, the first pull cover 146, and the second pull cover 148. Depending upon the dual clutch mechanism 116, other stop temperatures may also be read, including from the housing air 150 or from bell housing case 122 and the ambient air.
Step 514: Read/Load Time Lapse.
The method 500 read, loads, or determines the time lapse. The control system may include, or be in communication with, a clock or counter. The time lapse is the duration of time between the vehicle shut-down and the vehicle start-up.
Step 516: Housing Air Temperature Known?
The method 500 determines whether the temperature of the housing air 150 is known. If the initial temperature of the housing air 150 is known at vehicle start-up, the initial temperature model and the method 500 can be simplified. The results of this step may be pre-determined and programmed into the control system for powertrains 100 either will include, or will not include the housing air temperature sensor 152.
Step 518: Determine Case Temperature.
If the temperature of the housing air 150 is not known, the method 500 determines the initial temperature of the bell housing case 122. The initial temperature of the bell housing case 122 is determined as a function of the previous temperature differential between the ambient air and the bell housing case 122 when the vehicle previously shut-off, the current (or starting) ambient air temperature, the time lapse, and the heat transfer coefficient. The ambient air sensor 154 measures the initial ambient air temperature. The heat transfer coefficient may be determined from a lookup table.
Step 520: Determine Housing Air Temperature.
With the initial temperature of the bell housing case 122, the method 500 determines the initial temperature of the housing air 150 filling the bell housing case 122. The initial temperature of the housing air 150 is determined as a function of the previous temperature differential between the housing air 150 and the bell housing case 122 when the vehicle previously shut-off, the current (or starting) bell housing case 122, the time lapse, and the heat transfer coefficient.
Step 522: Determine Number of Segments.
The method 500 will determine the number of segments to be used in as the initial temperature model calculates the starting temperatures of the dual clutch mechanism 116. The method 500 may determine that a single segment—and a single calculation—is sufficient, or the method 500 may divide the time lapse into multiple segments.
Step 524: Calculate Clutch and Center Plate Temperatures.
The method 500 applies the initial temperature model to determine the starting temperatures of the first clutch 132, the second clutch 134, and the center plate 136. This calculation includes using internal loops to recalculate the heat transfer coefficient between the specific component and the housing air 150 based upon the temperature differential for each segment. As the temperature differential changes, the heat transfer coefficient also changes.
The method 500 calculates a start temperature for each component—the first clutch 132, the second clutch 134, and the center plate 136—across each time segment. Then, the start temperature for each segment is used as the stop temperature for the next segment. The start temperature from the final segment is the desired initial temperature and may be used for the five-state or seven-state thermal model as the models determine the component temperatures during vehicle operation.
Step 526: Calculate Pull Cover Temperatures.
The method uses the initial temperature model to determine the temperature of the first pull cover 146. The initial temperature model uses a linear approach during the convergence time and then set the temperature of the first pull cover 146 equal to the temperature of the first clutch 132 after the convergence time.
Step 528: Output Initial Temperatures.
The method 500 executing a control action with the determined initial temperatures. The control action may include outputting the determined temperatures to the control system for storage or use in other processes. When the method 500 is running as a sub-process of the method 200 shown in FIG. 2, the control action includes sending or outputting the initial temperatures to the method 200 as part of the five-state or the seven-state thermal model.
The detailed description and the drawings or figures are supportive and descriptive of the invention, but the scope of the invention is defined solely by the claims. While the best mode, if known, and other embodiments for carrying out the claimed invention have been described in detail, various alternative designs and embodiments exist for practicing the invention defined in the appended claims.

## Claims

1. A method for determining initial temperatures for a dry dual clutch mechanism at vehicle start-up, comprising:
determining a time lapse from a vehicle shut-down to the vehicle start-up;
determining a housing air start temperature of housing air within a bell housing case of the dry dual clutch mechanism at vehicle start-up;
reading a first clutch stop temperature of a first clutch at vehicle shut-down;
reading a housing air stop temperature of the housing air at vehicle shut-down;
determining a heat transfer coefficient between the first clutch and the housing air;
determining a first clutch start temperature from:
the heat transfer coefficient between the first clutch and the housing air,
a temperature differential between the first clutch stop temperature and the housing air stop temperature, and
the housing air start temperature; and

executing a control action using the determined first clutch start temperature.

2. The method of claim 1, further comprising:
reading a second clutch stop temperature of a second clutch at vehicle shut-down;
determining a heat transfer coefficient between the second clutch and the housing air;
determining a second clutch start temperature from:
the heat transfer coefficient between the second clutch and the housing air,
a temperature differential between the second clutch stop temperature and the housing air stop temperature, and
the housing air start temperature; and

executing a control action with the determined second clutch start temperature.

3. The method of claim 2, wherein determining the housing air start temperature includes measuring with housing air start temperature with a housing air sensor.

4. The method of claim 3, further comprising:
dividing the time lapse into a plurality of segments;
determining the first clutch start temperature for each of the plurality of segments, wherein the first clutch start temperature determined from one of the plurality of segments becomes the first clutch stop temperature for the next of the plurality of segments.

5. The method of claim 4, further comprising:
reading a first pull cover stop temperature of a first pull cover at vehicle shut-down;
comparing the time lapse to a convergence time;
determining a first pull cover start temperature, including:
if the time lapse is greater than the convergence time, setting the first pull cover start temperature equal to the first clutch start temperature, and
if the time lapse is less than the convergence time, applying a linear approach function between the first pull cover stop temperature and the temperature of the first clutch at the convergence time.

6. The method of claim 2, wherein determining the housing air start temperature does not include measuring the housing air start temperature, and the method further includes:
measuring an ambient air start temperature;
reading an ambient air stop temperature of the ambient air at vehicle shut-down;
reading a bell housing case stop temperature of the bell housing case at vehicle shut-down;
determining a heat transfer coefficient between the bell housing case and the ambient air;
determining a bell housing case start temperature from:
the heat transfer coefficient between the bell housing case and the ambient air,
a temperature differential between the bell housing case stop temperature and the ambient air stop temperature, and
the ambient air start temperature;

determining a heat transfer coefficient between the housing air and the bell housing case; and
determining the housing air start temperature as a function of:
the heat transfer coefficient between the housing air and the bell housing case,
a temperature differential between the housing air stop temperature and the bell housing case stop temperature, and
the determined bell housing case stop temperature.

7. A method for determining initial temperatures for a dry dual clutch mechanism at vehicle start-up, comprising:
determining a time lapse from a vehicle shut-down to the vehicle start-up;
determining a housing air start temperature of housing air within a bell housing case of the dry dual clutch mechanism at vehicle start-up, wherein the housing air start temperature is not measured, and includes:
measuring an ambient air start temperature;
reading an ambient air stop temperature of the ambient air at vehicle shut-down;
reading a bell housing case stop temperature of the bell housing case at vehicle shut-down;
determining a heat transfer coefficient between the bell housing case and the ambient air;
determining a bell housing case start temperature from:
the heat transfer coefficient between the bell housing case and the ambient air,
a temperature differential between the bell housing case stop temperature and the ambient air stop temperature, and
the ambient air start temperature;

determining a heat transfer coefficient between the housing air and the bell housing case; and
determining the housing air start temperature as a function of:
the heat transfer coefficient between the housing air and the bell housing case,
a temperature differential between the housing air stop temperature and the bell housing case stop temperature, and
the determined bell housing case stop temperature,


reading a first clutch stop temperature of a first clutch at vehicle shut-down;
reading a housing air stop temperature of the housing air at vehicle shut-down;
determining a heat transfer coefficient between the first clutch and the housing air;
determining a first clutch start temperature from:
the heat transfer coefficient between the first clutch and the housing air,
a temperature differential between the first clutch stop temperature and the housing air stop temperature, and
the housing air start temperature; and

executing a control action using the determined first clutch start temperature.