Power transmission device having friction clutch and controller configured to determine approximate temperature of friction clutch and responsively control friction clutch

Abstract

A power transmission device includes a friction clutch, an actuator, and a controller configured to determine an approximate temperature change of the friction clutch. The controller is configured to: determine a current power state of the friction clutch; determining a desired power state change based on the current power state and the previous power state; determining a plurality of thermal coefficients based on the thermal coefficient model, the desired power state change, and the set of operational variables; determining an approximate temperature change of the friction clutch based on the thermal coefficient and a friction clutch temperature model; determining an approximate clutch temperature based on the approximate temperature change and a contemporaneous value of the device ambient temperature; and controlling operation of the actuator based at least on the approximate clutch temperature.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Patent Application No. 17 / 706,904, filed on March 29, 2022, which in turn claims the benefit of U.S. Provisional Patent Application No. 63 / 316,698, filed on March 4, 2022. The disclosure of each of the above-referenced applications is incorporated herein by reference as if fully set forth herein. Technical Field

[0003] The present disclosure generally relates to a power transfer device having a friction clutch and a controller configured to determine an approximate temperature of the friction clutch and responsively control the friction clutch. Background Art

[0004] This section provides background information related to the present disclosure which is not necessarily prior art.

[0005] It is quite common for power transmission devices such as power take-off units, transfer cases, differentials, and axle assemblies to use friction clutches to control the amount of rotational power transmitted between rotating input and output members. The friction clutch uses a clutch pack having two sets of lamellae or plates that are staggered with each other, and each set of lamellae or plates is non-rotatably coupled to an associated one of the rotating input and output members. An actuator is used to apply a compressive force on the clutch pack to frictionally engage the two sets of plates with each other to resist relative rotation. The amount of torque that can be transmitted by the friction clutch is generally proportional to the magnitude of the compressive force applied by the actuator. In the event that the instantaneous torque difference between the rotating input and the rotating output exceeds the instantaneous torque transmission capacity or current torque transmission capacity of the friction clutch, one set of plates will rotate relative to the other set of plates, which will generate a large amount of heat considering the magnitude of the friction between adjacent plates. The extreme temperatures in a friction clutch can not only damage the plates, which are often formed of relatively thin steel, but can also adversely affect the tribological properties of the plates. It is therefore quite common to use pressurized lubrication to lubricate and cool the friction clutch, and to monitor the temperature of the friction clutch using data from a temperature sensor mounted to the friction clutch.

[0006] Modern demands for low cost, high efficiency, and (reduced) packaging space tend to further emphasize the need for thermal management of friction clutches, while simultaneously creating pressure to remove temperature sensors that directly sense the temperature of the friction clutch (in an effort to reduce the cost of power transmission components). Although various algorithms have been developed to determine the temperature of the friction clutch without the use of dedicated temperature sensors, these algorithms generally appear to be based on overly simplified assumptions and generalizations, and therefore, do not seem to provide sufficiently accurate temperature estimates over the entire range of operating conditions. Summary of the invention

[0007] This section provides a general summary of the disclosure, and is not intended to be a comprehensive disclosure of its full scope or all of its features.

[0008] In one form, the present disclosure relates to a power transmission device including a friction clutch, an actuator, and a controller. The friction clutch has a clutch assembly and an application plate, wherein the application plate is movable along an axis. The actuator has an output member, which is movable between a first position and a second position along the axis. The output member, the application plate, and the clutch assembly are arranged in a force transmission path. The output member is movable from a first position to a second position along the axis to apply a relatively larger force to the clutch assembly through the force transmission path. The controller is configured to: determine a current power state of the friction clutch; determine an expected power state change based on the current power state and a previous power state; and determine a plurality of thermal coefficients based on a thermal coefficient model, the expected power state change, and an operating variable set. The plurality of thermal coefficients indicates at least two operating variables in the operating variable set, and the at least two operating variables have a nonlinear thermal effect on the thermal performance of the friction clutch. The controller is further configured to: determine an approximate temperature change of the friction clutch based on the thermal coefficient and the friction clutch temperature model; determine an approximate clutch temperature based on the approximate temperature change and a contemporaneous value of the device ambient temperature; and control the operation of the actuator based at least on the approximate clutch temperature.

[0009] Further areas of applicability will become apparent from the description provided herein.The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0011] Figure 1 is a cross-sectional view of a power transmission device constructed in accordance with the teachings of the present disclosure;

[0012] Figure 2Ais a graph illustrating the relationship between the temperature of the friction clutch and time at different torques;

[0013] Figure 2B is a graph illustrating the relationship between the temperature of the friction clutch and time at different clutch slip speeds;

[0014] Figure 2C is a graph illustrating the relationship between the temperature of the friction clutch and time at different ring gear speeds;

[0015] Figure 2D is a graph illustrating the relationship between the temperature of the friction clutch and time under different driving modes;

[0016] Figure 2E is a graph illustrating the effect of the temperature of a friction clutch on the heating rate and cooling rate of the friction clutch;

[0017] Figure 3 is an example block diagram of a controller according to the teachings of the present disclosure;

[0018] Figure 4 is a flow chart of an example clutch temperature determination routine in accordance with the teachings of the present disclosure;

[0019] Figure 5A , Figure 5B and Figure 5C is a flow chart of another example clutch temperature determination routine according to the teachings of the present disclosure;

[0020] Figure 6 is a flow chart of an example torque control routine according to the teachings of the present disclosure;

[0021] Figure 7 is a perspective partial cross-sectional view of a second power transfer device constructed in accordance with the teachings of the present disclosure; and

[0022] Figure 8 is a cross-sectional view of a portion of a third power transmission device constructed in accordance with the teachings of the present disclosure.

[0023] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0024] refer to Figure 1, an exemplary power transmission device constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral 10. In the example provided, the power transmission device is an axle assembly, but it will be appreciated that the teachings of the present disclosure are applicable to various other types of power transmission devices including power output units, differential assemblies, transfer cases, and (rotating) couplings. The power transmission device 10 may include a housing 12, an input pinion 14, a ring gear 16, a differential assembly 18, a first output shaft 20, an intermediate shaft 22, a friction clutch 24, a second output shaft 26, an actuator 28, and a controller 30.

[0025] The housing 12 defines a first rotational axis 34, a second rotational axis 36, and an internal cavity 38 in which the input pinion 14, the ring gear 16, the differential assembly 18, the intermediate shaft 22, and the friction clutch 24 are housed. The input pinion 14 is rotatable about the first rotational axis 34 relative to the housing 12. The ring gear 16 meshes with the input pinion 14 and is rotatable about the second rotational axis 36 relative to the housing 12.

[0026] The differential assembly 18 includes a differential input member 40 coupled to the ring gear 16 for rotation therewith about the second axis of rotation 36 and a first differential output member 42 and a second differential output member 44, respectively rotatable about the second axis of rotation 36 relative to the differential input member 40. In the particular example provided, the differential assembly 18 includes an epicyclic or planetary gear train in which the differential input member 40 is an internal gear, the first differential output member 42 is a planet carrier, the second differential output member 44 is a sun gear, and a plurality of planet gears 48 are journaled by the planet carrier (i.e., the first differential output member 42) and meshingly engaged with the internal gear (i.e., the differential input member 40) and the sun gear (i.e., the second differential output member 44). However, it will be appreciated that the differential assembly 18 may employ straight bevel gearing or helical gearing in the alternative.

[0027] The first output shaft 20 is rotatable about the second axis of rotation 36 and is coupled to the first differential output member 42 for rotation therewith. The intermediate shaft 22 is rotatable about the second axis of rotation 36 and is coupled to the second differential output member 44 for rotation therewith.

[0028] The friction clutch 24 includes a first clutch member 50, a second clutch member 52, a clutch pack 54, and an apply plate 56. In the example provided, the first clutch member 50 is an internally-splined or toothed drum and is coupled to the intermediate shaft 22 for rotation therewith, while the second clutch member 52 is an externally-splined or toothed hub and is coupled to the second output shaft 26 for common rotation about the second rotation axis 36. Accordingly, the first clutch member 50 and the second clutch member 52 serve as input and output of the friction clutch 24, respectively. The clutch pack 54 generally includes a set of first thin plates or clutch plates 60 and a set of second thin plates or clutch plates 62. The first clutch plates 60 are non-rotatably but axially slidably coupled to the first clutch member 50, while the second clutch plates 62 are interleaved with the first clutch plates 60 and are non-rotatably but axially slidably coupled to the second clutch member 52. In the example provided, the first clutch plate 60 has external teeth that engage with the internal teeth of the first clutch member 50, and the second clutch plate 62 has internal teeth that engage with external teeth formed on the second clutch member 52. The apply plate 56 can be non-rotatably but axially slidably coupled to one of the first clutch member 50 and the second clutch member 52. In the example provided, the apply plate 56 has an internally-splined or toothed aperture (not specifically shown) that is received on the second clutch member 52 and is closely matingly engaged with external teeth formed on the second clutch member 52.

[0029] The actuator 28 can be any type of device or mechanism for moving the apply plate 56 along the second rotational axis 36 to selectively apply or adjust the compressive force applied to the clutch assembly 54. In the example provided, the actuator 28 includes an electric motor / pump assembly 70 and a hydraulic cylinder assembly 72. The hydraulic cylinder assembly 72 includes an annular cylinder 74 and an annular piston 76, which is concentrically formed in the housing 12 around the second rotational axis 36, and an annular piston 76 is accommodated in the annular cylinder 74 and is movable between a first position and a second position along the second rotational axis 36. It will be appreciated that in the example provided, the annular piston 76 is the "output member" of the actuator 28. The electric motor / pump assembly 70 is configured with a pump (not specifically shown) that provides pressurized hydraulic fluid to the annular cylinder 74 to drive the annular piston 76 (i.e., the output member of the actuator 28) along the second rotational axis 36 from the first position to the second position. It will be appreciated that the annular piston 76, the apply plate 56, and the clutch assembly 54 are disposed in the force transmission path 80, and that movement of the annular piston 76 from the first position to the second position will correspondingly cause the apply plate 56 to move along the second axis of rotation 36, thereby transmitting a relatively greater force to the clutch assembly 54 through the force transmission path 80. In the example provided, when the annular piston 76 is in the first position, no force is transmitted through the force transmission path 80, and therefore no torque or only a relatively small torque can be transmitted through the friction clutch 24. However, it will be appreciated that the first position can be set or selected so that a force with an amplitude greater than zero is transmitted through the force transmission path 80, so that the friction clutch 24 is always able to transmit a predetermined minimum torque therethrough. Optionally, the pump of the electric motor / pump assembly 70 is reversible so that it can also draw hydraulic fluid from the annular cylinder 74 to allow the annular piston 76 to move along the second axis of rotation 36 to the first position (e.g., via a plurality of return springs 84).

[0030] The controller 30 is configured to determine an approximate temperature of the friction clutch 24 and control the operation of the actuator 28 based at least on the determined temperature of the friction clutch 24. In the example provided, the controller 30 operates the electric motor / pump assembly 70 based at least on the approximate temperature of the friction clutch 24, thereby controlling the force applied to the apply plate 56 by the annular piston 76 (i.e., the output member of the actuator 28). If desired, the actuator 28 and / or other parts of the power transmission device 10 may include one or more sensors that assist the controller 30 in operating the actuator 28. For example, the actuator 28 may include a pressure sensor (not shown) that senses the pressure of the fluid output by the electric motor / pump assembly 70 and generates a pressure sensor signal in response. As another example, the controller 30 may be configured to determine the pressure of the fluid output by the electric motor / pump assembly 70 based on the rotational speed of an element of the electric motor / pump assembly 70 (e.g., a motor of the electric motor / pump assembly 70) or based on the power or current supplied to the electric motor of the electric motor / pump assembly 70. In yet another example, the power transmission device 10 is configured to include a temperature sensor to detect a device ambient temperature of the power transmission device, which is provided to the controller 30 for use in determining an approximate temperature of the friction clutch, as described herein. The approximate temperature of the friction clutch 24 may also be referred to as an "approximate clutch temperature," and the device ambient temperature may also be referred to as an "ambient temperature."

[0031] The controller 30 is configured to communicate with other controllers and / or sensors provided in a vehicle system having the power transmission device 10 by means of a vehicle communication network (not shown). For example, the controller 30 is configured to receive torque from a traction system controller. In one form, the torque command may indicate a requested amount of torque to be applied to the friction clutch 24, or may include data used by the controller 30 to determine the requested amount of torque. In another example, the controller 30 is configured to receive data indicating a drive mode from an engine controller of the vehicle system. In another example, the controller 30 may receive data related to the speed of one or more wheels of the vehicle system from the engine controller and / or from sensors provided at the wheels. Although specific examples are provided, the controller 30 may receive other data via a vehicle communication network.

[0032] To determine the approximate clutch temperature of the friction clutch 24, the controller 30 is configured to employ a multivariate thermal regression model that considers a number of factors or operating variables that affect the clutch temperature. More specifically, Table 1 below provides a non-limiting example of operating variables used to determine the approximate clutch temperature.

[0033] Table 1: Examples of manipulated variables

[0034]

[0035]

[0036] In some applications, the operating variable may have a nonlinear correlation with the temperature of the friction clutch (ie, clutch temperature), which may increase the complexity of estimating the clutch temperature. For example, FIG. 2A to FIG. 2E The graph shows the effects of selected operating variables on clutch temperatures of selected power transfer devices. Figure 2A The clutch temperature over time is provided for torque set to 200 Nm and 750 Nm, with the clutch slip speed and wheel speed held constant (e.g., clutch slip speed is 100 RPM and wheel speed is 800 RPM). The clutch temperature increases as the torque increases, and begins to decrease nonlinearly over time regardless of the torque.

[0037] In another example, Figure 2B The clutch temperature over time is provided for clutch slip speeds of 100 Nm and 200 Nm at constant torque (e.g., 750 Nm) and constant wheel speed (e.g., 800 RPM). Similar to the case of torque, the clutch temperature increases with increasing clutch slip speed, and for a given clutch slip speed, the clutch temperature decreases nonlinearly over time.

[0038] In another example, Figure 2C The figure shows the difference in clutch temperature for ring gear speeds of 50RPM and 800RPM under constant torque (e.g., 750Nm) and constant clutch slip speed (e.g., 100RPM). As shown, although the heating characteristics of the friction clutch are different at different ring gear speeds, the cooling characteristics of the friction clutch are more prominent, so that the friction clutch cools faster when the ring gear speed is 800RPM than at 50RPM. Although the differential 18 includes a hypoid ring gear 18, the differential can be configured to include other types of gears, such as wheel-shaped bevel gears. Accordingly, the term "ring gear speed" is not intended to limit the application of the present disclosure to hypoid ring gears, and can be more generally referred to as a differential input speed.

[0039] In another example, Figure 2DThe figure shows the difference in the rate at which the clutch temperature cools over time when the drive mode is provided as two-wheel drive (2WD) and four-wheel drive (4WD) with the friction clutch disengaged (i.e., the torque of the friction clutch is zero). In particular, in 2WD, the plates of the friction clutch are disengaged and fully opened, allowing lubricant to flow through the gaps between the plates. In 4WD, the plates of the friction clutch are disengaged but may contact each other, thereby reducing the amount of lubricant flowing between the plates. Figure 2C As shown in FIG, the clutch temperature for both drive modes starts at 200°C, but in 2WD, the clutch temperature cools faster than in 4WD. Accordingly, the cooling characteristics of the friction clutch and thus the clutch temperature may depend on the drive mode.

[0040] In some applications, variables that remain constant over time may have a compounding effect on clutch temperature. Specifically, the heating and / or cooling characteristics of the friction clutch may vary due to the continuous application of a constant torque to the friction clutch. For example, Figure 2E , for a continuous command, the torque applied to the friction clutch is 750Nm, the clutch slip speed is 100RPM, and the ring gear speed is 100rpm. Over time, after continuous commands, the amount of change in clutch temperature may vary as the friction clutch heats and cools. For example, in Figure 2E , the clutch temperature increases by approximately 156°C and decreases by 91°C, as indicated by arrows 201 and 202. After a period of time, and with torque, clutch slip speed, and ring gear speed constant, the rate at which the clutch temperature increases and decreases may begin to change, such that the clutch temperature increases by 116°C and decreases by 112°C, as indicated by arrows 203 and 204. That is, the friction clutch may begin to heat up slower and cool down faster. Accordingly, the clutch temperature from a previous determination may be used in a feedback loop for subsequent determinations of the clutch temperature to account for the compounding effects that selected operating variables may have on the clutch temperature.

[0041] It should be easy to understand. FIG. 2A to FIG. 2E It is provided for explanation purposes only and is not intended to limit the scope of the present disclosure. For example, the operating variables used to determine clutch temperature should not be limited to torque, clutch slip speed, ring gear speed, and drive mode. In addition, FIG. 2A to FIG. 2E The values ​​provided in are examples only and are not intended to represent an ideal or even nominal response of clutch temperature.

[0042] refer to Figure 3, an example block diagram of the controller 30 is provided. The controller 30 includes an operating variable module 302, a clutch temperature estimation module 304, and an actuator control module 308. The operating variable module 302 is configured to obtain an operating variable for determining an approximate clutch temperature. Based on the type of the operating variable, the operating variable module 302 can use predefined information to determine the operating variable and / or receive the operating variable from other devices (e.g., sensors and / or other controllers).

[0043] More specifically, in one form, the operating variable module 302 includes a received variable data storage 310, a variable determination module 312, and a composite variable data storage 314. The received variable data storage 310 is configured to obtain operating variables received from other devices, such as but not limited to torque, drive mode (e.g., data indicating the drive mode of the vehicle, which may include 2WD, 4WD or other drive modes), wheel speed and / or ambient temperature of the power transmission device 10, and other operating variables.

[0044] The variable determination module 312 is configured to determine various operating variables using stored information such as, but not limited to, formulas, models, and / or correlation data (e.g., the correlation data may be provided in a lookup table). For example, the variable determination module 312 is configured to determine: power as a function of torque and clutch slip speed; ring gear speed as a function of the wheel speeds of the right front wheel and the left front wheel; clutch inner basket speed as a function of the ring gear speed and the wheel speed of the left rear wheel; and clutch slip speed as a function of the clutch inner basket speed, the wheel speed of the right rear wheel, and the drive mode. The variable determination module 312 may also be configured to determine other operating variables, such as initial clutch temperature and energy input, etc., and should not be limited to the examples provided herein.

[0045] The composite variable data store 314 is configured to obtain selected operating variables that affect subsequent determinations of the approximate clutch temperature. For example, the power employed in the first determination of the approximate clutch temperature is used in subsequent determinations of the approximate clutch temperature to determine whether the power is increased or decreased from a previous determination. Accordingly, the composite variable data store 314 obtains the power determined based on the current determination of the approximate clutch temperature and provides the power for subsequent determinations. In another example, in the event of an increase in power, the energy generated based on the increase is used to determine the approximate temperature change for subsequent determinations when the power is reduced. It should be readily understood that the composite variable data store 314 is configured to obtain and provide different types of operating variables employed in subsequent determinations and should not be limited to the examples provided herein. In a non-limiting example, the received variable data store 310 and the composite variable data store 314 are provided as registers within a processor and / or as registers within a separate memory circuit.

[0046] As used herein, "determination" of the approximate clutch temperature refers to continuous or time-based determination of the approximate clutch temperature as long as the engine is on. In one form, the rate at which the determination is made is based on a processor clock employed by the controller 30, the rate at which other devices provide data, and other factors. In another form, the rate of determination may be based on a user-defined cycle time.

[0047] The clutch temperature estimation module 304 is configured to determine the approximate clutch temperature using a multivariate thermal regression model having a thermal coefficient model 316 and a friction clutch temperature model 318. More specifically, the clutch temperature estimation module 304 is configured to determine an initial clutch temperature in an ignition cycle (i.e., when the engine is on) and adjust the initial clutch temperature based on the approximate temperature change determined by the multivariate thermal regression model. Using the set of operating variables, the thermal coefficient model 316 is configured to determine values ​​of a plurality of thermal coefficients to be provided to the friction clutch temperature model 318 to determine the approximate temperature change of the friction clutch 24.

[0048] In one form, a multivariate thermal regression model is defined as having coefficients of a friction clutch temperature model 318 determined by another set of regression equations provided as a thermal coefficient model 316. For purposes of explanation only, Equation 1 represents an example of a friction clutch temperature model that is a nonlinear regression equation based on a time counter, where Y is the rate of temperature change, and t_cnt is the time counter reading. In Equation 1, A and B are thermal coefficients, and the values ​​of the thermal coefficients are determined by Equations 2A and 2B. Equations 2A and 2B are different forms of regression equations, where x1, x2...x8 represent calculated or directly received operating variables, and a, b, c, d, e, f, m, n, o, p and rare coefficients.

[0049] Equation 1…Y = A*Exp(B*t_cnt)

[0050] Equation 2A…A=a*x1 2 +b*x2 2 +c*x1+d*x2+e*x1*x2+f

[0051] Equation 2B…B=m*x1 2 +m*x2 2 +o*x1+p*x2+q*x1*x2+r

[0052] In one form, the thermal coefficient model 316 is defined using a data set representing the effect of selected operating variables on the temperature of the friction clutch 24. FIG. 2A to FIG. 2EA coefficient model for associating a selected operating variable with clutch temperature is defined using a data set similar to the data set provided in (in which clutch temperature is provided over time and with changing values ​​of selected operating variables). In a non-limiting example, the data set can be obtained through controlled experiments / tests and / or through a computational fluid dynamics thermal model designed to simulate the relationship between various operating variables and clutch temperature. In one form, the thermal coefficient model 316 includes a coefficient model for each operating variable in the set of operating variables that affects the clutch temperature. Specifically, a data set for a selected operating variable from the set of operating variables can be analyzed using a known statistical tool, wherein the statistical tool uses a regression modeling method such as nonlinear regression modeling to define a coefficient model, and the model captures the nonlinear relationship between the selected operating variable and the clutch temperature.

[0053] The friction clutch temperature model 318 is defined based on the operating variables (e.g., four or more operating variables) captured in the thermal coefficient model and, in some cases, correlation data. Specifically, the coefficient model for the set of operating variables is analyzed using known statistical tools that employ regression modeling methods to define the friction clutch temperature model 318 that outputs an approximate temperature change. In addition to data from the thermal coefficient model 316, the friction clutch temperature model 318 may also employ data from predetermined correlation data, such as a lookup table that relates values ​​of secondary operating variables not represented in the thermal coefficient model 316 to associated temperature changes used to determine the approximate temperature change. For example, instead of representing the drive mode in the thermal coefficient model 316, the friction clutch temperature model 318 may use a lookup table to capture the effect of the drive mode on the clutch temperature.

[0054] In one form, the thermal coefficient model 316 and the friction clutch temperature model 318 may include a power increase portion and a power reduction portion to characterize the heating characteristics and cooling characteristics of the friction clutch 24, respectively. Specifically, the cooling characteristics and heating characteristics of the friction clutch can be changed based on the value of the selected operating variable. In addition, when the torque increases, the influence of certain operating variables on the clutch temperature may be greater than when the torque decreases, and vice versa. Accordingly, the thermal coefficient model 316 can define a heat increase portion and a heat reduction portion. The heat increase portion includes a first group of coefficient models for a first group of operating variables among the operating variable set. The heat reduction portion includes a second group of coefficient models for a second group of operating variables among the operating variable set. The first group of operating variables includes at least one operating variable different from the second group of operating variables. In a non-limiting example, the first group of operating variables may include current power input, ring gear speed, and ambient temperature. In a non-limiting example, the second group of operating variables may include ring gear speed, ambient temperature, clutch slip speed, drive mode, and a desired power state change, which is the difference between the current power input and the previous power input. Accordingly, the friction clutch temperature model 318 may include a clutch temperature increase portion and a clutch temperature decrease portion. The clutch temperature increase portion determines an approximate temperature increase as an approximate temperature change based on data from the heat increase portion of the thermal coefficient model 316. The clutch temperature decrease portion determines an approximate temperature decrease as an approximate temperature change based on data from the heat decrease portion of the thermal coefficient model 316.

[0055] In one form, the clutch temperature estimation module 304 is configured to determine the initial clutch temperature at the beginning of the ignition cycle (i.e., when the engine is turned on) based on the approximate clutch temperature when the engine is turned off or in other words, when the engine is stopped (i.e., T_ESO), the engine shutdown time (i.e., the period or duration of the engine shutdown), and the ambient temperature of the power transmission device 10. In order to improve the accuracy of the initial clutch temperature, the clutch temperature estimation module 304 is configured to include a temperature initialization model, which is a function of the last approximate clutch temperature determined when the engine is turned off (i.e., the previous ignition approximate clutch temperature) and the engine shutdown time. Specifically, after the engine is turned off, the temperature of the friction clutch 24 begins to decrease, and the longer the engine is turned off, the colder the friction clutch becomes. Accordingly, the initial clutch temperature when the engine is stopped for one hour is different from the temperature when it is stopped for five hours. Accordingly, the initial clutch temperature can also be an operating variable. The temperature initialization model can be defined using a data set that provides the approximate clutch temperature when the engine is stopped and the effect of the engine shutdown time on the clutch temperature. As with the thermal coefficient model 316 and the friction clutch temperature model 318, the temperature initialization model may be defined using known statistical tools and employing regression modeling methods. In lieu of the temperature initialization model, the clutch temperature estimation module 304 may employ correlation data that relates the approximate clutch temperature at engine stop, the engine stop time, and the ambient temperature to the initial clutch temperature.

[0056] In one form, the clutch temperature estimation module 304 is configured to determine the non-engagement temperature change (i.e., ΔT_NoPwr) as an approximate temperature change when no torque is applied (i.e., non-engagement state) based on a set of operating variables selected from the set of operating variables. In one form, the set of operating variables includes ring gear speed, clutch slip speed, drive mode, and ambient temperature. In an example application, the clutch temperature estimation module 304 is configured to use a non-engagement temperature model that is a regression-based model determined using a data set that provides the effects of ring gear speed, clutch slip speed, drive mode, and ambient temperature on clutch temperature. In another example, the clutch temperature estimation module 304 uses related data such as a lookup table to determine the non-engagement temperature.

[0057] In one form, in response to receiving the torque command, the clutch temperature estimation module 304 is configured to determine whether the torque (or more specifically, power) is increasing or decreasing. If the power is increasing (i.e., the increase in power can be referred to as the power increase state of the friction clutch 24), the clutch temperature estimation module 304 is configured to determine an approximate temperature increase (ΔT_Inc) as an approximate temperature change based on a first set of operating variables, data indicating the duration of the power increase, and a multivariate regression thermal model (i.e., for example, the heat increase portion of the thermal coefficient model 316 and the clutch temperature increase portion of the friction clutch temperature model 318). If the power is decreasing (i.e., the decrease in power can be referred to as the power decrease state of the friction clutch 24), the clutch temperature estimation module 304 is configured to determine an approximate temperature decrease (ΔT_Dec) as an approximate temperature change based on a second set of operating variables, data indicating the duration of the power decrease, and a multivariate regression thermal model (i.e., for example, the heat decrease portion of the thermal coefficient model 316 and the clutch temperature decrease portion of the friction clutch temperature model 318). In one form, the clutch temperature estimation module 304 uses one or more counters to track the power increase duration and the power reduction duration. In one variation, the clutch temperature estimation module 304 is configured to determine the approximate temperature increase / decrease without tracking the power increase duration or the power reduction duration.

[0058] In one form, during a power reduction, the clutch temperature estimation module 304 is configured to consider the energy input generated during the previous power increase as an operating variable used in the multivariate regression model. That is, if at the time of the first determination, the power is increasing, the clutch temperature estimation module 304 is configured to determine the energy input that affects the temperature of the friction clutch 24 when the power is reduced. In one form, the energy input is based on the power input and the duration of the power increase. Accordingly, in a subsequent determination when the power is reduced, the clutch temperature estimation module 304 is configured to use the energy input to determine the approximate temperature reduction.

[0059] In one form, the clutch temperature estimation module 304 is configured to determine the approximate clutch temperature as the sum of the approximate temperature change and the ambient temperature (i.e., the contemporaneous value of the device ambient temperature). The approximate clutch temperature change at one determination is provided for subsequent determinations of the approximate temperature change and may be referred to as the cumulative temperature change (ΔT_Cum). Accordingly, the approximate clutch temperature determined by the multivariate regression thermal model is a function of previous approximate clutch temperature change determinations.

[0060] The actuator control module 308 is configured to control the operation of the actuator based at least on the approximate clutch temperature. In an example application, the actuator control module 308 is configured to execute a limited torque mode to inhibit or reduce the occurrence of overheating of the friction clutch 24. Specifically, the actuator control module 308 compares the approximate clutch temperature with a first temperature threshold to determine whether the approximate clutch temperature is greater than the first temperature threshold. If greater than, the actuator control module 308 enters a limited torque mode in which the actuator control module 308 controls the actuator to provide a first reduced torque output. The first temperature threshold is provided as a value less than the maximum allowable clutch temperature, and therefore, the actuator control module 308 begins to control the actuator to address the problem of excessive approximate clutch temperature. In one form, the first reduced torque output is less than the maximum torque output of the actuator (e.g., the first reduced torque output <50% of the maximum torque output).

[0061] In the limited torque mode, the actuator control module 308 is configured to determine whether the approximate clutch temperature is greater than a second temperature threshold that is greater than the first temperature threshold. That is, the approximate clutch temperature may continue to increase even with the reduced torque output. In one form, the second temperature threshold is greater than the first temperature threshold and less than or equal to the maximum allowable temperature of the friction clutch 24.

[0062] If the approximate clutch temperature is greater than the second temperature, the actuator control module 308 is configured to provide a zero torque output until the approximate clutch temperature decreases to a value less than or equal to a third temperature threshold. In one form, the third temperature threshold is less than the first threshold. Accordingly, once the approximate clutch temperature is less than or equal to the third temperature threshold, the actuator control module 308 is configured to exit the limited torque mode and control the actuator to provide the necessary torque provided in the torque command.

[0063] In one form, instead of a tiered torque limiting approach, the actuator control module 308 is configured to inhibit torque output once the approximate clutch temperature reaches a single temperature threshold.

[0064] The controller 30 may be configured in various suitable ways to perform the functions described above. Figure 4 , an example clutch temperature determination routine 500 executed by the controller 30 is provided. In one form, when the engine is turned on (ie, ignition cycle) and the controller 30 ( Figure 3) is turned on, routine 500 is executed. At 502, the controller 30 obtains the engine off time (EOT) and the current values ​​of various operating variables, such as, but not limited to: the approximate clutch temperature (T_ESO) when the engine was last stopped, wheel speed, ambient temperature and / or drive mode. At 504, the controller 30 determines the initial clutch temperature (T_InitClutch) based on the engine off time (EOT) and the approximate clutch temperature (T_ESO) when the engine was stopped. At 506, the controller 30 determines the initial clutch temperature (T_InitClutch) based on the requested and applied to the friction clutch 24 ( Figure 1 ) torque (Trq) and clutch slip speed (S_CS) (ie, the first clutch member 50 and the second clutch member 52 ( Figure 1 ) to calculate the current power input (Pwr).

[0065] At 508, the controller 30 determines the value of one or more thermal coefficients based on the thermal coefficient model 316 and the set of operating variables. At 510, the controller 30 determines an approximate clutch temperature change (ΔT_Clutch) that approximates the change in the approximate clutch temperature (T_AprClutch) from its previous value based on the thermal coefficients and the friction clutch temperature model 318. At 512, the controller 30 determines the approximate clutch temperature (T_AprClutch) based on the ambient temperature (T_Amb) and the approximate clutch temperature change (ΔT_Clutch), and more specifically, as the sum of the ambient temperature (T_Amb) and the approximate clutch temperature change (ΔT_Clutch).

[0066] At 514, the controller 30 stores the current value of the approximate clutch temperature (T_AprClutch) in a designated non-volatile memory, and then, routine 500 returns to 502 to obtain the current value of the operating variable to estimate the approximate clutch temperature. Accordingly, when the engine is off and the controller 30 is off, the value of the approximate clutch temperature (T_AprClutch) is stored and can be used as the last approximate clutch temperature (T_ESO) when the engine was last stopped when the engine is subsequently turned on (i.e., a new ignition cycle). At 516, the controller 30 obtains the current operating variables and returns to 506 to perform a subsequent determination of the approximate clutch temperature (T_AprClutch). In one form, routine 500 ends when the controller 30 is off.

[0067] refer to FIG. 5A to FIG. 5C, another clutch temperature determination routine (i.e., clutch temperature determination routine 600) is provided. As with routine 500, routine 600 is performed when the engine is on (i.e., ignition cycle) and the controller 30 is on. At 602, the controller 30 obtains the engine off time (EOT) and current values ​​of various operating variables, such as, but not limited to, the value of the approximate clutch temperature (T_ESO) when the engine was last stopped, wheel speed, ambient temperature, and / or driving mode.

[0068] At 604, the controller 30 determines an initial clutch temperature (T_InitClutch) based on the engine off time (EOT) and the approximate clutch temperature when the engine was last stopped (T_ESO). At 606, the controller 30 determines the change in clutch temperature when no torque is applied to the friction clutch 24, which may also be referred to as a no-power temperature change (ΔT_NoPwr), based on the initial clutch temperature (T_InitClutch) and one or more operating variables (such as, but not limited to: ring gear speed, clutch slip speed, ambient temperature, and drive mode). More specifically, when the engine is first started, the friction clutch 24 is typically not engaged. However, the clutch temperature may still change due to other factors, and therefore, routine 600 takes into account changes that may occur in the temperature of the friction clutch 24 during the non-engagement period. Once the change is determined, the no-power clutch temperature change (ΔT_NoPwr) will be provided as a cumulative temperature change (ΔT_Cum) for subsequent determination of the approximate clutch temperature. At 608 , the controller 30 determines the approximate clutch temperature (T_AprClutch) based on the ambient temperature (T_Amb) and the no-power temperature change (ΔT_NoPwr). Specifically, the controller 30 determines the approximate clutch temperature (T_AprClutch) as the sum of the ambient temperature (T_Amb) and the no-power temperature change (ΔT_NoPwr).

[0069] Additionally, the controller 30 stores the current value of the approximate clutch temperature (T_AprClutch) in a designated non-volatile memory at 608. Accordingly, when the engine is turned off and the controller 30 is turned off, the value of the approximate clutch temperature (T_AprClutch) is stored and can be used as the last approximate clutch temperature (T_ESO) when the engine was last stopped when the engine is subsequently turned on (i.e., a new ignition cycle).

[0070] At 610, the controller 30 determines whether a torque command is received. If a torque command is not received, the controller 30 proceeds to 612 to obtain the current value of the operating variable. Since the friction clutch 24 is not engaged, the controller proceeds to 614 to determine the no-power temperature change (ΔT_NoPwr) as the approximate temperature change based on one or more operating variables, including the cumulative temperature change (ΔT_Cum) from the previous determination of the approximate clutch temperature (T_AprClutch). The controller 30 then returns to 608 to determine the approximate clutch temperature (T_AprClutch).

[0071] If a torque command is received, the controller 30 proceeds to 616 to obtain the current value of the operating variable. At 618, the controller 30 determines the current power input (Pwr) based on the torque (Trq) to be applied to the friction clutch 24 and the clutch slip speed (S_CS), and then determines the expected power state change (ΔPwr) (i.e., power change) based on the current power input (Pwr) and the power input at the previous determination from the approximate clutch temperature (T_AprClutch). Specifically, if a torque command is received at the previous determination, the power input (Pwr) calculated at the previous determination is used in a subsequent determination in which a torque command is also received to determine the power change (ΔPwr). Accordingly, if a torque command is not received at the previous determination, the power change (ΔPwr) is equal to the power input (Pwr) determined at 618.

[0072] At 620, the controller 30 determines whether the power change (ΔPwr) is greater than or equal to zero. Specifically, the controller 30 determines whether the torque applied to the friction clutch 24 is increasing / unchanged or decreasing. If the torque is increasing / unchanged, the controller 30 proceeds to 622 to clear the temperature decrease counter (T_DecCnt) associated with tracking the decreasing power input (i.e., the decrease in torque of the friction clutch 24) and increment the temperature increase counter (T_IncCnt) associated with tracking the increasing / unchanged power input (i.e., the increase / unchanged amount of torque of the friction clutch 24, and generally referred to as the power increase state). Using these counters, the controller 30 can track how long the temperature of the friction clutch 24 has been decreasing or increasing. The temperature decrease counter (T_DecCnt) and the temperature increase counter (T_IncCnt) may also be referred to as a power decrease counter and a power increase counter, respectively.

[0073] At 624, the controller 30 determines a thermal coefficient value for the increase in temperature based on the thermal coefficient model 316 and the operating variables (i.e., specifically, a first set of operating variables). For example, the first set of operating variables includes the current power input (Pwr), the ring gear speed, the ambient temperature (T_Amb), and the cumulative temperature change (ΔT_Cum) from the previous determination. At 626, the controller 30 determines the incremental temperature change (i.e., ΔT_Inc) based on the thermal coefficient and the friction clutch temperature model 318. More specifically, in one form, the incremental temperature change (ΔT_Inc) is determined using the heat incremental portion of the thermal coefficient model 316 and the clutch temperature incremental portion of the friction clutch temperature model 318.

[0074] If the controller 30 determines that the power change (ΔPwr) is less than zero (i.e., the decrease in power input indicates a decrease in torque of the friction clutch 24 and a power reduction state), the controller 30 proceeds to 628 to clear the temperature increase counter (T_IncCnt) and increment the temperature decrease counter (T_DecCnt). At 630, the controller 30 determines a thermal coefficient value for the decrease in temperature based on the thermal coefficient model 316 and one or more operating variables (i.e., specifically, a second set of operating variables). For example, the second set of operating variables includes the power change (ΔPwr), the ring gear speed, the ambient temperature (T_Amb), the drive mode, and the cumulative temperature change (ΔT_Cum) from the previous determination. At 632, the controller 30 determines the decrease temperature change (i.e., ΔT_Dec) based on the thermal coefficient and the friction clutch temperature model 318. More specifically, in one form, the heat reduction portion of the thermal coefficient model 316 and the clutch temperature reduction portion of the friction clutch temperature model 318 are employed to determine the decrease temperature change (ΔT_Dec).

[0075] From 626 or 632, the controller 30 determines a cumulative temperature change (ΔT_Cum) (i.e., an approximate temperature change) that approximates the change in the approximate clutch temperature (T_AprClutch) from its previous value. The cumulative temperature change (ΔT_Cum) is used for subsequent determination of the approximate clutch temperature (T_AprClutch). In one form, the cumulative temperature change (ΔT_Cum) is the sum of the increasing temperature change (ΔT_Inc) and the decreasing temperature change (ΔT_Dec). Accordingly, if the controller 30 determines an increase in torque of the friction clutch 24 and determines an increasing temperature change, the decreasing temperature change will be zero. Therefore, the cumulative temperature change is equal to one of the increasing temperature change, the decreasing temperature change, and the powerless temperature change. At 636, the controller 30 determines the approximate clutch temperature (T_AprClutch) based on the ambient temperature and the cumulative temperature change. Specifically, the approximate clutch temperature (T_AprClutch) is provided as the sum of the ambient temperature and the cumulative temperature change.

[0076] At 638, the controller 30 stores the current value of the approximate clutch temperature (T_AprClutch) in a designated non-volatile memory and returns to 610 to perform a subsequent determination of the approximate clutch temperature (T_AplClutch). Accordingly, when the engine is turned off and the controller 30 is turned off, the value of the approximate clutch temperature (T_AprClutch) is stored and can be used as the last approximate clutch temperature (T_ESO) when the engine was last stopped when the engine is subsequently turned on (i.e., a new ignition cycle). In one form, routine 600 ends when the controller 30 is turned off.

[0077] It should be readily appreciated that the clutch temperature determination routines 500 and 600 may be configured in other suitable manners and should not be limited to Figure 4 as well as FIG. 5A to FIG. 5C For example, after a first determination in which the approximate clutch temperature change is an increasing temperature change, in a subsequent second determination in which the torque is decreasing, a decreasing temperature change is determined using the energy input as the manipulated variable.

[0078] refer to Figure 6, an example torque control routine 700 performed by the controller 30 is provided. In one form, the controller 30 is configured to perform the torque control routine 700 when the controller 30 is turned on and after calculating the approximate clutch temperature (T_AprClutch). At 702, the controller 30 determines whether the current value of the approximate clutch temperature (T_AprClutch) is greater than or equal to the first temperature threshold (T_Th1). If the current value of the approximate clutch temperature (T_AprClutch) is less than the first temperature threshold (T_Th1), the controller 30 proceeds to 704 to control the actuator to provide torque (Trq) to the friction clutch 24 based on the torque of the torque command (Trq_Cmd). That is, the torque (Trq) applied to the friction clutch 24 is not limited, or in other words, it is a normal torque output based on the torque command.

[0079] If the current value of the approximate clutch temperature (T_AprClutch) is greater than or equal to the first temperature threshold (T_Th1), the controller 30 controls the torque to be applied based on the limited torque mode. Specifically, the controller 30 proceeds to 706 to determine whether the torque of the torque command (Trq_Cmd) is greater than the limited torque output (Trq_RO). If the controller 30 determines that the torque of the torque command (Trq_Cmd) is greater than the limited torque output (Trq_RO), the controller 30 proceeds to 708 to control the actuator to provide a reduced torque to the friction clutch 24. For example, the applied torque (Trq) is reduced to the limited torque output (ie, Trq=Trq_RO), where the limited torque output is less than the maximum allowable torque (Trq_Max) of the friction clutch 24 (e.g., Trq_RO<50%*Trq_Max). If the controller 30 determines that the torque of the torque command (Trq_Cmd) is less than the limited torque output (ie, Trq_RO), the controller 30 proceeds to 710 to control the actuator to apply the torque of the torque command (Trq_Cmd) to the friction clutch 24 (ie, Trq=Trq_Cmd).

[0080] As described above, the controller 30 recalculates the approximate clutch temperature until the controller 30 is shut down, and once in the limited torque mode, the controller 30 continues to evaluate the approximate clutch temperature in the limited torque mode until the approximate clutch temperature decreases to a value less than or equal to the third temperature threshold. Specifically, the controller 30 proceeds to 712 to determine whether the current value of the approximate clutch temperature (T_AprClutch) is greater than or equal to the second temperature threshold (T_Th2) greater than the first temperature threshold (T_Th1). If the approximate clutch temperature (T_AprClutch) is greater than or equal to the second temperature threshold (T_Th2), the controller 30 proceeds to 714 to inhibit torque output (i.e., Trq=0). After no torque output, or if the approximate clutch temperature (T_AprClutch) is less than the second temperature threshold (T_Th2), the controller 30 proceeds to 716 to determine whether the approximate clutch temperature (T_AprClutch) is less than or equal to the third temperature threshold (T_Th3) less than the first temperature threshold (T_Th1). If the approximate clutch temperature (T_AprClutch) is not less than the third temperature threshold (T_Th3), the controller 30 remains in the limited torque mode by returning to 712. If the approximate clutch temperature (T_AprClutch) is less than or equal to the third temperature threshold (T_Th3), the controller 30 exits the limited torque mode and proceeds to 704 of routine 700 to provide the torque provided in the torque command to the clutch (i.e., Trq=TrqCmd). More specifically, once the approximate clutch temperature (T_AprClutch) is greater than the second temperature threshold (T_Th2), the friction clutch 24 will not engage until the approximate clutch temperature (T_AprClutch) is less than or equal to the third temperature threshold (T_Th3) that is less than the first temperature threshold (T_Th1). In one form, routine 700 ends when the controller 30 is turned off.

[0081] It should be readily appreciated that the torque control routine 700 may be configured in other suitable ways and should not be limited to Figure 6 For example, instead of a stratified torque limiting approach, the controller 30 may inhibit torque output once the approximate clutch temperature reaches a defined temperature threshold.

[0082] While the actuator 28 is illustrated and described as having an output member that moves along the second axis of rotation 36 in response to the application of fluid pressure, it should be appreciated that the actuator may be configured differently.

[0083] exist Figure 7In the embodiment of the present invention, the power transfer device 10a includes a differential assembly 18a, and an actuator 28a including a ball-ramp mechanism 100, a plurality of pins 102, an electric motor 104, and an actuator gear train 106. The ball-ramp mechanism 100 is conventional in that it includes a first ball-ramp ring 110, a second ball-ramp ring 112, and a plurality of balls 114. The first ball-ramp ring 110 is disposed on a bushing 120, which is mounted on a differential input member 40a (i.e., a differential case in the illustrated example) of the differential assembly 18a. The bushing 120 allows the first ball-ramp ring 110 to rotate relative to the differential case 40a about the rotation axis 36a of the differential case 40a. The second ball ramp ring 112 is non-rotatably but axially slidably disposed on the bushing 120 and, therefore, can rotate about the rotation axis 36a and axially move along the rotation axis 36a relative to the differential case 40a. Each of the balls 114 is received in a pair of ball tracks 130 and 132 formed in the first ball ramp ring 110 and the second ball ramp ring 112, respectively. The depth of each of the ball tracks 130 and 132 gradually decreases in the circumferential direction. Each of the pins 102 is received in an associated pin hole 140 formed longitudinally through the differential case 40a. The pin holes 140 (and the pins 102 therefrom) are circumferentially spaced about the rotation axis 36a of the differential case 40a. The thrust bearing 142 and the thrust washer 144 are disposed between the second ball ramp ring 112 and the first axial end of the pin 102, while the second opposite axial end of the pin 102 abuts against the apply plate 56a of the friction clutch 24a. In this example, the first clutch member 50a is unitarily and integrally formed with the differential case 40a, while the second clutch member 52a is non-rotatably coupled to the side gear 148 (i.e., the differential output member). The actuator gear train 106 includes an input gear 150 and an output gear 156, the input gear 150 being coupled to the motor output shaft 152 of the electric motor 104 for rotation therewith, and the output gear 156 being coupled to the first ball ramp ring 110 for common rotation about the rotation axis 36a of the differential assembly 18a. In the example provided, the input gear 150 is meshingly engaged with the output gear 156, but it should be appreciated that the actuator gear train 106 may employ one or more additional gears between the input gear 150 and the output gear 156. The electric motor 104 is selectively operable to rotate the first ball ramp ring 110 to cause corresponding rotational movement of the balls 114 in the ball tracks 140 and 132 between the deep end and the shallow end of the ball tracks 130 and 132 .The balls 114 are located at the deep end of the ball tracks 130 and 132, the second ball ramp ring 112 is spaced a first distance from the first ball ramp ring 110 along the rotational axis 36a, and the balls 114 are located at the shallow end of the ball tracks 130 and 132, so that the second ball ramp ring 112 is spaced a second distance greater than the first distance from the first ball ramp ring 110 along the rotational axis 36a. Accordingly, the electric motor 104 can be operated to rotate the first ball ramp ring 110 and selectively position the pin 102 (i.e., the output member of the actuator 28a in the example provided) between a first position (corresponding to the balls 114 being placed at the deep end of the ball tracks 130 and 132) and a second position (corresponding to the balls 114 being placed at the shallow end of the ball tracks 130 and 132) along the rotational axis 36a to control the force transmitted to the clutch assembly 54a through the force transmission path 80a. The controller 30a is configured to determine an approximate temperature of the friction clutch 24a and control the operation of the actuator 28a based at least on the determined temperature of the friction clutch 24a. In the example provided, the controller 30a operates the electric motor 104 based at least on the approximate temperature of the friction clutch 24a to control the force applied by the pin 102 (i.e., the output member of the actuator 28a) to the apply plate 56a.

[0084] The controller 30a is configured to determine an approximate temperature of the friction clutch 24a and to control the operation of the actuator 28a based at least on the determined temperature of the friction clutch 24a. The controller 30a is configured in a similar manner to the controller 30, and therefore, a description of the controller 30a is omitted for brevity.

[0085] exist Figure 8, the power transmission device 10b is a transfer case, and the actuator 28b includes a ball ramp mechanism 100b and an electromagnet 200. The ball ramp mechanism 100b is conventional in that it includes a first ball ramp ring 110b, a second ball ramp ring 112b, and a plurality of balls 114b. The first ball ramp ring 110b is disposed on the rear output shaft 206 of the transfer case 10b. The first ball ramp ring 110b is coupled to the rear output shaft 206 to rotate with it around the rotation axis 36b of the rear output shaft 208. The thrust bearing 210 and the stop ring 212 limit the axial movement of the first ball ramp ring 110b along the rotation axis 36b in the opposite direction to the friction clutch 24b. The second ball ramp ring 112b is mounted on the rear output shaft 106 in a manner that allows both relative rotation around the rotation axis 36b and axial movement along the rotation axis 36b relative to the rear output shaft 206. Each of the balls 114b is accommodated in a pair of ball tracks 130b and 132b formed in the first ball ramp ring 110b and the second ball ramp ring 112b, respectively. The depths of the ball tracks 130b and 132b gradually decrease in the circumferential direction. The electromagnet 200 includes an electromagnetic coil 220 and an armature 222. The electromagnetic coil 220 is fixedly coupled to the housing 12b of the transfer case 10b and is selectively operable to generate a magnetic field. The armature 222 is non-rotatably but axially slidably coupled to the second clutch member 52b (i.e., the output member coupled to the friction clutch 24b). In the example provided, the armature 222 includes a plurality of external teeth (not specifically shown) that meshingly engage with a plurality of internal teeth (not specifically shown) formed on the second clutch member 52b. The first clutch member 50b is rotatably coupled to the rear output shaft 206, and the second clutch member 52b is rotatably coupled to a sprocket 230 engaged with a chain 232. The chain 232 is engaged to a second sprocket (not shown) which is rotatably coupled to the front output shaft (not shown). The electromagnetic coil 220 can be energized to generate a magnetic field that acts on the armature 222, thereby moving the armature 222 along the rotational axis 36b (relative to the second clutch member 52) into engagement with the second ball ramp ring 112b. The torsional resistance or resisting force on the second clutch member 52b caused by various components such as the chain 232 and the front output shaft is transmitted from the armature 222 to the second ball ramp ring 112b and causes the second ball ramp ring 112 to rotate about the rotation axis 36b relative to the first ball ramp ring 110b and causes corresponding rotational movement of the balls 114b in the ball tracks 130b and 132b (i.e., from their deep ends to their shallow ends).The balls 114 are located at the deep end of the ball tracks 130b and 132b, so that the second ball ramp ring 112b is spaced apart from the first ball ramp ring 110b by a first distance (i.e., at a first position) along the rotation axis 36b, while the balls 114b are located at the shallow end of the ball tracks 130b and 132b, so that the second ball ramp ring 112b is spaced apart from the first ball ramp ring 110b by a second distance (i.e., at a second position) along the rotation axis 36b. The second distance is greater than the first distance. The second ball ramp ring 112b (in the example provided, the output member of the actuator 28b) contacts the apply plate 56b when it moves from the first position to the second position. Accordingly, the electromagnetic coil 220 can be operated to control the force transmitted to the clutch assembly 54b through the force transmission path 80b. The controller 30b is configured to determine an approximate temperature of the friction clutch 24b and control the operation of the actuator 28b based at least on the determined temperature of the friction clutch 24b. In the example provided, the controller 30b operates the solenoid 220 based on at least the approximate temperature of the friction clutch 24b to control the force applied by the second ball ramp ring 112b (ie, the output member of the actuator 28b) to the apply plate 56b.

[0086] The controller 30b is configured to determine an approximate temperature of the friction clutch 24b and control the operation of the actuator 28b based at least on the determined temperature of the friction clutch 24b. The controller 30b is configured in a similar manner to the controller 30, and therefore, a description of the controller 30b is omitted for brevity.

[0087] For the purpose of illustration and description, the foregoing description of various embodiments is provided. It is not intended to be exhaustive or to limit the present disclosure. The individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but where applicable, they are interchangeable and may be used in selected embodiments even if not specifically shown or described. The same situation may also be different in many ways. These changes should not be considered as departing from the present disclosure, and all these modifications are intended to be included within the scope of the present disclosure.

[0088] Example embodiments are provided to make the present disclosure thorough and to fully convey the scope of the present disclosure to those skilled in the art. Many specific details, such as examples of specific components, devices, and methods, are set forth to provide a thorough understanding of the embodiments of the present disclosure. It will be appreciated by those skilled in the art that specific details need not be employed, and that example embodiments may be embodied in many different forms, and none should be construed as limiting the scope of the present disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0089] The terms used herein are only used to describe specific example embodiments and are not intended to be limiting. As used herein, the singular forms "one", "an" and "the (described)" may be intended to also include plural forms unless the context clearly indicates otherwise. The terms "comprise", "comprising", "including" and "having" are inclusive, and therefore, specify the presence of the narrated features, wholes, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, parts and / or their groups. The method steps, processes and operations described herein should not be interpreted as having to be performed in the specific order discussed or described, unless specifically designated as the order of execution. It should also be understood that additional or alternative steps can be adopted.

[0090] As used herein, the phrase “at least one of A, B, and C” should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least another of C.” As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0091] In this application, the terms "controller" and / or "module" may refer to, be part of, or include an application-specific integrated circuit (ASIC); a digital, analog, or mixed analog / digital discrete circuit; a digital, analog, or mixed analog / digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other appropriate hardware components that provide the described functionality; or a combination of some or all of the above components (such as in a system on a chip).

[0092] The term "memory circuit" is a subset of the term "computer-readable medium". The term "computer-readable medium" as used herein does not include transient electrical or electromagnetic signals propagated through a medium (such as on a carrier wave); the term "computer-readable medium" may therefore be considered to be tangible and non-transitory. Non-limiting examples of non-transitory, tangible computer-readable media are non-volatile memory circuits (such as flash memory circuits, erasable programmable read-only memory circuits, or mask read-only circuits), volatile memory circuits (e.g., static random access memory circuits or dynamic random access memory circuits), magnetic storage media (e.g., analog or digital magnetic tape or hard disk drives), and optical storage media (such as CDs, DVDs, or Blu-ray discs).

[0093] The devices and methods described in this application can be implemented in part or in full by a special-purpose computer created by configuring a general-purpose computer to perform one or more specific functions contained in a computer program. The functional blocks and flow chart elements and other elements described above are used as software specifications, which can be converted into computer programs through routine work by skilled technicians or programmers.

[0094] The description of the present disclosure is merely exemplary in nature, and therefore, various changes that do not depart from the essence of the present disclosure are intended to fall within the scope of the present disclosure. Such changes should not be regarded as departing from the spirit and scope of the present disclosure.

Claims

1. A power transmission device, comprising: a friction clutch having a clutch assembly and an apply plate, the apply plate being movable along an axis; an actuator having an output member movable along the axis between a first position and a second position, wherein the output member, the apply plate, and the clutch assembly are disposed in a force transmission path, wherein the output member is movable along the axis from the first position to the second position to apply a relatively greater force to the clutch assembly through the force transmission path; as well as The controller is configured as: determining a current power state of the friction clutch; determining a desired power state change based on the current power state and a previous power state; determining a plurality of thermal coefficients based on a thermal coefficient model, the desired power state change, and a set of operating variables, wherein the plurality of thermal coefficients are indicative of at least two operating variables in the set of operating parameters, and the at least two operating variables have a nonlinear thermal effect on thermal characteristics of the friction clutch; determining an approximate temperature change of the friction clutch based on the thermal coefficient and a friction clutch temperature model; determining an approximate clutch temperature based on the approximate temperature change and a contemporaneous value of a device ambient temperature, and Operation of the actuator is controlled based at least on the approximate clutch temperature.

2. The power transmission device according to claim 1, wherein: The friction clutch temperature model and the thermal coefficient model are based on a regression modeling approach.

3. The power transmission device according to claim 1, wherein: The set of operating variables includes torque, clutch slip speed, differential input speed, drive mode, the device ambient temperature, and a previous fired approximate clutch temperature.

4. The power transmission device according to claim 1, wherein: The controller is configured to: An initial clutch temperature in a firing cycle is determined based on a previous firing approximate clutch temperature, an engine off time, and the device ambient temperature, wherein the approximate clutch temperature is further based on the initial clutch temperature.

5. The power transmission device according to claim 4, wherein: The controller is configured to: The initial clutch temperature is determined using a temperature initialization model, wherein the temperature initialization model is based on a regression modeling approach.

6. The power transmission device according to claim 4, wherein: The controller is configured to determine: determining whether the current power state is zero; and In response to the current power state being zero, a non-engagement temperature change from the initial clutch temperature is determined, wherein the non-engagement temperature change is determined based on a non-engagement temperature model and a set of operating variables selected from the set of operating variables.

7. The power transmission device according to claim 6, wherein: The set of operating variables includes differential input speed, clutch slip speed, drive mode, and the device ambient temperature.

8. The power transmission device according to claim 1, wherein: The controller is configured to: determining whether the expected power state change indicates a power increase state or a power decrease state; responsive to the desired power state change being the power increase state, incrementing a temperature increase counter; responsive to the desired power state change being the power reduction state, incrementing a temperature reduction counter; determining an approximate temperature increase as the approximate temperature change based on a value of the temperature increase counter, a first set of operating variables, and the set of operating variables including the first set of operating variables in response to the expected power state change indicating the power increase state; and In response to the expected power state change indicating the power reduction state, determining an approximate temperature reduction as the approximate temperature change based on a value of the temperature reduction counter, a second set of operating variables, wherein the set of operating variables includes the second set of operating variables, and wherein the first set of operating variables includes at least one operating variable different from the second set of operating variables.

9. The power transmission device according to claim 8, wherein: The first set of operating variables includes the current power state, the differential input speed, and the device ambient temperature, and The second set of operating variables includes the desired power state change, the differential input speed, the device ambient temperature, a clutch slip speed, and a drive mode.

10. The power transmission device according to claim 8, wherein: The controller is configured to: determining an energy input in response to the desired power state change indicating the power increase state, wherein the energy input is based on the current power state and a value of the temperature increase counter, and The energy input is used to determine the approximate temperature reduction for a subsequent determination in response to the expected power state change indicating the power reduction state.

11. The power transmission device according to claim 1, wherein: The controller is configured to: The approximate temperature change is stored as a previous approximate temperature change, and a subsequent approximate temperature change is determined based on the previous approximate temperature change.

12. The power transmission device according to claim 1, wherein: The controller is configured to: The approximate clutch temperature is determined based on a previous approximate temperature change from a previous determination of the approximate clutch temperature.

13. The power transmission device according to claim 1, wherein: The controller is configured to: determining whether the approximate clutch temperature is greater than a first temperature threshold; and In response to the approximate clutch temperature being greater than the first temperature threshold, the actuator is controlled to provide a limited torque output, wherein the limited torque output is less than a maximum torque output of the actuator.

14. The power transmission device according to claim 13, wherein: The controller is configured to: determining whether the approximate clutch temperature is greater than a second temperature threshold, wherein the second temperature threshold is greater than the first temperature threshold; and In response to the approximate clutch temperature being greater than the second temperature threshold, the actuator is controlled to provide a zero torque output.

15. The power transmission device according to claim 14, wherein: The controller is configured to: determining whether the approximate clutch temperature is less than or equal to a third temperature threshold, wherein the third temperature threshold is less than the first temperature threshold; and In response to the approximate clutch temperature being less than or equal to the third temperature threshold, the actuator is controlled to perform a normal torque output, wherein the normal torque output is based on a torque command.

16. A power transmission device, comprising: a friction clutch having a clutch assembly and an apply plate, the apply plate being movable along an axis; an actuator having an output member movable along the axis between a first position and a second position, wherein the output member, the apply plate, and the clutch assembly are disposed in a force transmission path, wherein the output member is movable along the axis from the first position to the second position to apply a relatively greater force to the clutch assembly through the force transmission path; as well as The controller is configured as: determining a current power state of the friction clutch; determining an initial clutch temperature in a firing cycle based on a previous firing approximate clutch temperature, engine off time, and device ambient temperature; determining whether the current power state is zero; determining a non-engagement temperature change from the initial clutch temperature in response to the current power state being zero, wherein the non-engagement temperature change is an approximate temperature change; In response to the current power state being non-zero; In response to the current power state being not zero, determining a desired power state change based on the current power state and a previous power state, determining a plurality of thermal coefficients based on a thermal coefficient model, the desired power state change, and a set of operating variables, wherein the plurality of thermal coefficients are indicative of at least two operating variables in the set of operating parameters, and the at least two operating variables have a nonlinear thermal effect on thermal characteristics of the friction clutch; and determining an approximate temperature change of the friction clutch based on the thermal coefficient and a friction clutch temperature model; determining an approximate clutch temperature based on the approximate temperature change and a contemporaneous value of a device ambient temperature; and Operation of the actuator is controlled based at least on the approximate clutch temperature.

17. The power transmission device according to claim 16, wherein: The controller is configured, in response to the power being non-zero: determining whether the expected power state change indicates a power increase state or a power decrease state; responsive to the desired power state change being the power increase state, incrementing a temperature increase counter; responsive to the desired power state change being the power reduction state, incrementing a temperature reduction counter; determining an approximate temperature increase as the approximate temperature change based on a value of the temperature increase counter, a first set of operating variables, and the set of operating variables including the first set of operating variables in response to the expected power state change indicating the power increase state; and In response to the expected power state change indicating the power reduction state, determining an approximate temperature reduction as the approximate temperature change based on a value of the temperature reduction counter, a second set of operating variables, wherein the set of operating variables includes the second set of operating variables, and wherein the first set of operating variables includes at least one operating variable that is different from the second set of operating variables.

18. The power transmission device according to claim 17, wherein: The first set of operating variables includes the current power state, the differential input speed, and the device ambient temperature, and The second set of operating variables includes the desired power state change, the differential input speed, the device ambient temperature, a clutch slip speed, and a drive mode.

19. The power transmission device according to claim 16, wherein: The controller is configured to: determining whether the approximate clutch temperature is greater than a first temperature threshold; and In response to the approximate clutch temperature being greater than the first temperature threshold, the actuator is controlled to provide a limited torque output, wherein the limited torque output is less than a maximum torque output of the actuator.

20. The power transmission device according to claim 19, wherein: The controller is configured to: determining whether the approximate clutch temperature is greater than a second temperature threshold, wherein the second temperature threshold is greater than the first temperature threshold; in response to the approximate clutch temperature being greater than the second temperature threshold, controlling the actuator to provide a zero torque output; In response to the approximate clutch temperature being less than the second temperature threshold, determining whether the approximate clutch temperature is less than or equal to a third temperature threshold, wherein the third temperature threshold is less than the first temperature threshold; as well as In response to the approximate clutch temperature being less than or equal to the third temperature threshold, the actuator is controlled to perform a normal torque output, wherein the normal torque output is based on a torque command.

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