Clutch temperature estimation for a mobile machine

A mobile machine includes a propulsion system. The propulsion system may include a prime mover, a traction device, and a clutch operable to transmit power produced by the prime mover to the traction device. The propulsion system may also include propulsion-system controls operable to control the clutch. The propulsion-system controls may include at least one information processor configured to estimate a temperature of the clutch based at least in part on an estimated slippage of the clutch and a fluid temperature.

TECHNICAL FIELD

The present disclosure relates to mobile machines and, more particularly, mobile machines that use one or more clutches.

BACKGROUND

Mobile machines typically have a propulsion system for propelling them. The propulsion system of a mobile machine may include one or more traction devices (such as wheels), a prime mover (such as an engine), and components for transmitting power from the prime mover to the one or more traction devices to propel the mobile machine. In some propulsion systems the components for transmitting power from the prime mover to the one or more traction devices include one or more clutches. These clutches can be slipped to modulate the transmission of power between the components of the propulsion system for various purposes, such as for starting movement of the mobile machine and/or controlling distribution of power to the traction devices of the mobile machine as part of a traction control strategy. Unfortunately, slipping these clutches can generate significant heat, which can sometimes heat the clutches and/or other components to undesirably high temperatures.

U.S. Pat. No. 6,769,526 B2 to Iida et al. (“the '526 patent”) discloses a system for estimating the temperature of a clutch in a four-wheel-drive system. To estimate the temperature of the clutch, the system of the '526 patent estimates an amount of slippage of the clutch and an amount of torque transmitted by the clutch. Using these estimates, the system of the '526 patent estimates an amount of energy generated by the slippage of the clutch. To estimate whether the temperature of the clutch has increased, the system of the '526 patent compares the estimated value of the energy generated by the slippage of the clutch to a predetermined fixed value representative of an estimate of the amount of energy that may be typically rejected by the clutch.

Although the '526 patent discloses a system for estimating temperature increases of a clutch in a four-wheel-drive system, the system of the '526 patent may have certain shortcomings. For example, the approach of using a fixed value of assumed heat rejection rate to determine whether the clutch temperature has increased or decreased may estimate clutch temperatures with a level of accuracy that is undesirably low.

The disclosed embodiments solve one or more of the problems set forth above.

SUMMARY

One disclosed embodiment relates to a mobile machine having a propulsion system. The propulsion system may include a prime mover, a traction device, and a clutch operable to transmit power produced by the prime mover to the traction device. The propulsion system may also include propulsion-system controls operable to control the clutch. The propulsion-system controls may include at least one information processor configured to estimate a temperature of the clutch based at least in part on an estimated slippage of the clutch and a fluid temperature.

Another embodiment relates to a method of operating a mobile machine. The method may include producing power with a prime mover. The method may also include transmitting power from the prime mover to a traction device to propel the mobile machine, which may include controlling a clutch to transmit power produced by the prime mover to the traction device. The method may also include estimating with at least one information processor of the mobile machine a temperature of the clutch, which may include estimating the temperature based at least in part on an estimated slippage of the clutch and a fluid temperature.

A further disclosed embodiment relates to a mobile machine having a propulsion system configured to propel the mobile machine. The propulsion system may include a prime mover, at least one front traction device, at least one rear traction device, and a power-transfer system configured to transmit power from the prime mover to the at least one front traction device and the at least one rear traction device. The power-transfer system may include a clutch. The propulsion-system may also include propulsion-system controls configured to control the clutch to control a distribution between power transmitted to the at least one front traction device and power transmitted to the at least one rear traction device. The propulsion-system controls may include at least one information processor operable to estimate a temperature of the clutch. Additionally, the propulsion-system controls may be configured to fully engage the clutch in response to the estimated temperature of the clutch exceeding a reference value.

DETAILED DESCRIPTION

FIG. 1illustrates a mobile machine10according to the present disclosure. Mobile machine10may include a propulsion system12configured to propel mobile machine10. Mobile machine10may be configured to perform a variety of tasks. For example, mobile machine10may be configured to transport or move people, goods, or other matter or objects. Additionally, or alternatively, mobile machine10may be configured to perform a variety of other operations associated with a commercial or industrial pursuit, such as mining, construction, energy exploration and/or generation, manufacturing, transportation, and agriculture.

Propulsion system12may include a prime mover14, traction devices16, a power-transfer system18, and propulsion-system controls19. Prime mover14may include any type of component or components operable to provide power to propel mobile machine10. For example, in some embodiments, prime mover14may include an engine, such as a diesel engine, a gasoline engine, a gaseous-fuel-powered engine, or a gas turbine engine. Additionally, or alternatively, prime mover14may include one or more motors, such as one or more electric motors and/or one or more hydraulic motors.

Traction devices16may include any types of devices operable to receive power produced by prime mover14and propel mobile machine10by transmitting that power to the terrain underlying mobile machine10. For example, in some embodiments, each of traction devices16may be a wheel. Alternatively, traction devices16may include one or more track units or other types of components configured to propel mobile machine10. Propulsion system12may include any suitable number and/or arrangement of traction devices16. For example, asFIG. 1shows, the traction devices16of propulsion system12may include a right front traction device16RF, a left front traction device16LF, a right rear traction device16RR, a left rear traction device16LR, a right center traction device16RC, and a left center traction device16LC.

Power-transfer system18may include any components operable to transmit power between prime mover14and traction devices16. For example, asFIG. 1shows, power-transfer system18may include a transmission20, a transfer case22, a front axle24, a rear axle28, a center axle26, and drive shafts30,32, and34. Transmission20may be configured to transmit power from prime mover14to transfer case22. Additionally, transmission20may be configured to provide a number of optional drive ratios between prime mover14and transfer case22, including a finite number of drive ratios or a continuously variable range of drive ratios. Transfer case22may be configured to transmit power received from prime mover14and transmission20to drive shafts30and32. Drive shaft30may be connected to transmit power from transfer case22to front axle24, and front axle24may be configured to transmit power to right front traction device16RF and left front traction device16LF. Similarly, drive shaft32may be connected to transmit power from transfer case22to center axle26, and center axle26may be configured to transmit power from driveshaft32to right center traction device16RC and left center traction device16LC. Drive shaft34may similarly be connected to transmit power from center axle26to rear axle28, and rear axle28may be configured to transmit power from driveshaft34to right rear traction device16RR and left rear traction device16LR.

Power-transfer system18may also include one or more clutches for controlling the transmission of power between prime mover14and traction devices16. For example, asFIG. 1shows, power-transfer system18may include clutches C1, C2, C3, and C4. Clutch C1may be connected between drive shafts30and32, such that clutch C1may be operated to control the distribution between power transmitted to the front traction devices16RF,16LF and power transmitted to the center and rear traction devices16RC,16LC,16RR,16LR. Clutch C1may, for example, be included in transfer case22. Each of clutches C2, C3, C4may be connected between one right traction device16RF,16RC,16RR and one left traction device16LF,16LC,16LR, such that each clutch C2, C3, C4is operable to control the distribution of power between the right and left traction devices it connects. In some embodiments, each clutch C2, C3, C4may be included within one of axles24,26,28.

Propulsion-system controls19may include any components operable to monitor and control propulsion system12in the manners discussed below. In some embodiments, propulsion-system controls19may include an information processor44operably connected to various sources of information and various control components, such that information processor44may monitor and control various aspects of the operation of mobile machine10. Information processor44may include any components operable to receive and process information. In some embodiments, information processor44may include one or more microprocessors (not shown) and/or one or more memory devices (not shown). Information processor44may be operatively connected to prime mover14, transmission20, and transfer case22in such a manner to allow information processor44to monitor and/or control various aspects of the operation of these components.

Additionally, propulsion-system controls19may include clutch control units46,48,50, and52associated with clutches C1, C2, C3, and C4, respectively. Clutch control units46,48,50, and52may be operably connected to information processor44in a manner allowing information processor44to monitor and/or control various aspects of the operation of clutch control units46,48,50, and52and clutches C1, C2, C3, and C4. Each clutch control unit46,48,50,52may include any components operable to control actuation of the associated clutch C1, C2, C3, C4under the control of information processor44. In some embodiments, clutch control units46,48,50,52may use hydraulic fluid from a hydraulic system (not shown) of mobile machine10to control clutches C1, C2, C3, C4. For example, each clutch control unit46,48,50,52may include a hydraulic actuator (not shown) connected to the clutch C1, C2, C3, C4and a control valve (not shown) for controlling the supply of hydraulic fluid to the hydraulic actuator to actuate the clutch C1, C2, C3, C4. In such embodiments, the control valve of each clutch control unit46,48,50,52may be an electrically controlled solenoid valve, and information processor44may be configured to send an electric control signal to the solenoid valve to control the associated clutch C1, C2, C3, C4. Additionally, in such embodiments, information processor44may receive information about the pressure of hydraulic fluid supplied to each clutch control unit46,48,50,52.

Information processor44may be configured (i.e., programmed) to perform a variety of tasks associated with monitoring and/or controlling propulsion system12. In some embodiments, information processor44may be configured to estimate a temperature of each of clutches C1, C2, C3, C4. For example, asFIG. 2shows, information processor44may be programmed with a clutch temperature estimation module54configured to estimate a temperature of each of clutches C1, C2, C3, C4. Clutch temperature estimation module54may have a number of inputs56and a number of outputs58. The outputs58may include an estimate C1TEMP of a temperature of clutch C1, an estimate C2TEMP of a temperature of clutch C2, an estimate C3TEMP of a temperature of clutch C3, and an estimate C4TEMP of a temperature of clutch C4.

The inputs56of clutch temperature estimation module54may include sensed values, estimated values, control signals generated by information processor44, and various other information. AsFIG. 2shows, in some embodiments, the inputs to the clutch temperature estimation module54may include a speed value SRF of right front traction device16RF, a speed value SLF of left front traction device16LF, a speed value SRC of right center traction device16RC, a speed value SLC of left center traction device16LC, a speed value SRR of right rear traction device16RR, and a speed value SLR of left rear traction device16LR. These speed values may be gathered in various ways. In some embodiments, information processor44may receive these speed values of traction devices16from sensors (not shown) configured to sense a rotational speed of each of traction devices16.

The inputs56to clutch temperature estimation module54may also include inputs C1TOR, C2TOR, C3TOR, and C4TOR indicative of an amount of torque transmitted through each of clutches C1, C2, C3, and C4, respectively. The clutch torque values may be determined in any suitable manner. In some embodiments, each clutch torque value C1TOR, C2TOR, C3TOR, and C4TOR may be estimated by propulsion-system controls19based on one or more sensor or control signals. For example, information processor44may estimate clutch torque value C1TOR based at least in part on the value of a control signal that information processor44sends to clutch control unit46associated with clutch C1. The value of the control signal sent to the clutch control unit46may be proportional to the torque transmitted by clutch C1because the clutch control unit46may engage clutch C1with an amount of force proportional to the value of the control signal. Information processor44may similarly estimate the clutch torque values C2TOR, C3TOR, and C4TOR associated with clutches C2, C3, and C4based at least in part on the values of the control signals sent to clutch control units48,50, and52. Information processor44may refine these estimates of the torque C1TOR, C2TOR, C3TOR, and C4TOR transmitted by clutches C1, C2, C3, and C4with information about the pressure of hydraulic fluid supplied to clutch control units46,48,50, and52, which may also affect the actuation force of each of clutches C1, C2, C3, and C4.

The inputs56to the clutch temperature estimation module54may also include values of one or more fluid temperatures. For example, clutch temperature estimation module54may receive an oil temperature value OIL1, which may be a temperature of oil in which clutch C1operates. Similarly, clutch temperature estimation module54may receive oil temperature values OIL2, OIL3, and OIL4, which may be temperatures of oil in which each of clutches C2, C3, and C4operate, respectively.

These temperature values may be gathered in various ways. For example, in some embodiments, oil temperature value OIL1may be sensed by a temperature sensor (not shown) in contact with the oil in which clutch C1operates. Additionally, in some embodiments, one or more of oil temperatures OIL1, OIL2, OIL3, OIL4may be estimated based on various other factors. For example, in embodiments where oil temperature OIL1is sensed, oil temperatures OIL2, OIL3, OIL4may be estimated based at least in part on the oil temperature OIL1. This may involve, for instance, assuming one or more of OIL2, OIL3, and OIL4to be the same temperature as OIL1. In some embodiments, this may provide a conservative estimate of OIL2, OIL3, and OIL4, as the oil temperature OIL1of the oil in which clutch C1operates may generally be higher than the oil temperatures OIL2, OIL3, and OIL4of the oil in which clutches C2, C3, and C4operate. Alternatively one or more of the oil temperatures OIL2, OIL3, OIL4may be estimated by adding a constant temperature to the oil temperature OIL1or by multiplying the oil temperature OIL1by a scaling factor. Any one of the oil temperatures OIL1, OIL2, OIL3, and OIL4may be estimated based at least in part on one or more of the other oil temperatures OIL1, OIL2, OIL3, and OIL4.

Additionally, one or more of the oil temperatures OIL1, OIL2, OIL3, and OIL4may be estimated based at least in part on factors other than the other oil temperatures OIL1, OIL2, OIL3, and OIL4. For example, one or more of the oil temperatures OIL1, OIL2, OIL3, and OIL4may be estimated based at least in part on a running time of propulsion system12(i.e., an amount of time that propulsion system12has been operating to propel mobile machine10). In some embodiments, propulsion-system controls19may determine one or more of the oil temperatures OIL1, OIL2, OIL3, and OIL4based at least in part on one or more sensed temperatures in combination with other factors like the running time of propulsion system12.

Additionally, in some embodiments, the values of one or more of oil temperatures OIL1, OIL2, OIL3, and OIL4may be determined based at least in part on one or more assumed values. Similarly, in some embodiments, one or more of the oil temperatures OIL1, OIL2, OIL3, and OIL4may be assumed values. In some embodiments where one or more of the oil temperatures OIL1, OIL2, OIL3, and OIL4are assumed or based on assumed values, the assumed values may be conservative values. For example, one or more of the oil temperatures OIL1, OIL2, OIL3, and OIL4and/or one or more of the values on which they are based may be assumed “worst case” values, i.e., values reflective of a maximum anticipated temperature.

Alternatively, in some embodiments, each of the oil temperature values OIL1, OIL2, OIL3, and OIL4may be sensed values. In such embodiments, propulsion-system controls19may include temperature sensors (not shown) that sense the temperature of the oil in which each of clutches C1, C2, C3, and C4operate.

Clutch temperature estimation module54may also receive an air temperature value AIR. This value may also be gathered in various ways. In some embodiments, the air temperature value AIR may be sensed by a sensor (not shown) configured to sense the temperature of ambient air that prime mover14intakes.

Based on inputs56, clutch temperature estimation module54may use various approaches to generate the estimated temperatures C1TEMP, C2TEMP, C3TEMP, and C4TEMP of clutches C1, C2, C3, C4. Details of some exemplary approaches that propulsion-system control19may use in clutch temperature estimation module will be discussed in greater detail below.

Mobile machine10, propulsion system12, propulsion-system controls19, and clutch temperature estimation module54are not limited to the configurations and operation discussed above and shown inFIGS. 1 and 2. For example, propulsion-system controls19may gather inputs56for clutch temperature estimation module54in manners other than those discussed above. Additionally, the inputs56and outputs58of clutch-temperature estimation module54may include information other than that shown inFIG. 2and/or omit some of the information shown inFIG. 2. Additionally, power-transfer system18may include different numbers and arrangements of clutches and other components than shown inFIG. 1. Similarly, propulsion system12may include different numbers and/or arrangements of traction devices16than shown inFIG. 1.

INDUSTRIAL APPLICABILITY

The disclosed embodiments may have use in any application where it may prove beneficial to control transmission of power in a propulsion system of a mobile machine at least in part with clutches. During propulsion of mobile machine10by propulsion system12, propulsion-system controls19may control clutches C1, C2, C3, C4in various ways to provide various benefits. For example, in some embodiments, propulsion-system controls19may control clutches C1, C2, C3, and C4as part of a traction-control system for biasing transmission of power to those traction devices16that have the best traction. This may involve propulsion-system controls19modulating (i.e., slipping) clutch C1to control the distribution between power transmitted to the front traction devices16RF,16LF and power transmitted to the center and rear traction devices16RC,16LC,16RR, and16RL. Simultaneously, propulsion-system controls19may modulate (i.e., slip) clutches C2, C3, and C4to control the distribution between power transmitted to the right-side traction devices16RF,16RC,16RR and power transmitted to the left-side traction devices16LF,16LC,16LR.

The slippage of clutches C1, C2, C3, and C4during such operation may generate significant heat. This may tend to increase the temperature of clutches C1, C2, C3, and C4. If the temperature of any of clutches C1, C2, C3, and C4climbs too high, such overheating may cause damage to the clutches C1, C2, C3, and C4themselves and/or to other components of propulsion system12. Propulsion-system controls19may monitor for any such overheating by monitoring the temperatures of clutches C1, C2, C3, and C4. For example, information processor44may use the inputs56and clutch temperature estimation module54shown inFIG. 2to determine estimated temperatures C1TEMP, C2TEMP, C3TEMP, and C4TEMP for each of clutches C1, C2, C3, and C4.

The clutch temperature estimation module may implement various approaches for determining the temperatures of clutches C1, C2, C3, and C4. In some embodiments, propulsion-system controls19may estimate an initial value C1TEMPI, C2TEMPI, C3TEMPI, and C4TEMPIfor each clutch C1, C2, C3, and C4, which may be a temperature of each clutch C1, C2, C3, and C4when propulsion system12has been inactive for an extended period of time. In some embodiments, propulsion-system controls19may assume that the initial temperatures C1TEMPI, C2TEMPI, C3TEMPI, and C4TEMPIof clutches C1, C2, C3, and C4are the same as the temperatures OIL1, OIL2, OIL3, and OIL4of the oil in which each of clutches C1, C2, C3, C4operate.

After propulsion system12begins propelling mobile machine10, propulsion-system controls19may periodically redetermine the temperatures C1TEMP, C2TEMP, C3TEMP, and C4TEMP of clutches C1, C2, C3and C4based on various operating parameters. For example, propulsion-system controls19may estimate how much the temperatures C1TEMP, C2TEMP, C3TEMP, and C4TEMP of clutches C1, C2, C3, and C4has increased or decreased after a period of time Δt.

Propulsion-system controls19may use various approaches for estimating the amount of increase or decrease in clutch temperatures C1TEMP, C2TEMP, C3TEMP, and C4TEMP over the interval Δt. In some embodiments, this may include determining a clutch slippage value for each clutch C1, C2, C3, and C4. The clutch slippage value for a clutch may represent a difference in speed between the two sides of the clutch, expressed either in terms of rotational speed of the two sides of the clutch or linear speed of the surfaces of the two sides of the clutch. Propulsion-system controls19may use various approaches to determine a clutch slippage value for any of clutches C1, C2, C3, and C4. In some embodiments, propulsion-system controls19may determine the slippage value for a given clutch C1, C2, C3, and C4based on the speeds of one or more of traction devices16and known drive ratios in power-transfer system18. For example, propulsion-system controls19may use the following equation to determine a clutch slippage value SLPC1for clutch C1:
SLPC1=Abs[(K1*(SRC+SLC))−(K2*(SRF+SLF))]

Where, K1and K2are constants related to known drive ratios in power-transfer system18, and SRC, SLC, SRF, and SLF are speeds of traction devices16RC,16LC,16RF, and16LF, respectively. Propulsion-system controls19may use similar equations to determine the slippage values for each of clutches C2, C3, and C4based on the speeds of one or more traction devices16and known drive ratios of power-transfer system18.

Propulsion-system controls18may use the determined slippage value for each of clutches C1, C2, C3, and C4in various ways in determining the temperature of each of clutches C1, C2, C3, and C4. In embodiments where the inputs to clutch temperature estimation module54include estimated values of torque C1TOR, C2TOR, C3TOR, and C4TOR transmitted by each of clutches, C1, C2, C3, and C4, propulsion-system controls19may use the estimated torque values in combination with the slippage values to determine a rate of heat generation for each clutch based on the determined torque and clutch slippage values. For example, propulsion-system controls19may determine a rate of heat generation HC1in clutch C1using the following equation:
HC1=C1TOR*SLPC1*K3

Where, SLPC1is the slippage value of clutch C1already determined, C1TOR is the estimated value of torque transmitted by clutch C1, and K3is a constant used for units conversion. Propulsion-system controls19may use similar equations to determine the rate of heat generation by each of clutches C2, C3, and C4based on the amount of torque and slippage of each of these clutches.

With the estimated rate of heat generation for a given clutch C1, C2, C3, C4, propulsion-system controls19may determine the amount of heat energy generated by that clutch in the period Δt by multiplying the rate of heat generation by the amount of time elapsed. For example, propulsion-system controls19may estimate the amount of heat energy generated EGC1by clutch C1during the period Δt with the following equation:
EGC1=HC1*Δt*K4

Where, HC1is the rate of heat generation already determined and K4is a constant related to the characteristics of clutch C1(such as the number of clutch plates in clutch C1) and constant values used in the numerical integration of power. Propulsion-system controls19may determine the amount of energy generated in any of clutches C2, C3, and C4during the time period Δt by using similar equations.

Having determined the amount of energy generated by a given clutch C1, C2, C3, C4in the period Δt, propulsion-system controls19may use this information in various ways in estimating the amount by which the temperature of a given clutch C1, C2, C3, C4has increased or decreased over the time period Δt. In some embodiments, propulsion-system controls19may estimate a net amount of energy absorbed by a given clutch C1, C2, C3, C4and use that information in combination with known thermal properties of the clutch C1, C2, C3, C4to determine an increase or decrease in the temperature of the clutch. For example, propulsion-system controls19may use the following equations to determine a change in the temperature of clutch C1over the period Δt:
ENC1=EGC1−ERC1
ΔTEMPC1=ENC1*K5

Where, ENC1is the net energy absorbed by clutch C1, EGC1is the amount of energy generated by clutch C1, ERC1is the amount of energy rejected by clutch C1during the same period, ATEMPC1is the change in temperature of the clutch C1over the period, and K5is a constant related to the thermal properties of clutch C1. Propulsion-system controls19may use similar equations to determine the change in temperature of any of clutches C2, C3, and C4over a given period of time.

The amount of energy rejected by a given clutch C1, C2, C3, C4over the time period Δt may be determined in various ways. In some embodiments, propulsion-system controls19may determine the net energy rejected by a clutch C1, C2, C3, C4based at least in part on one or more fluid temperatures. For example, propulsion-system controls19may determine the amount of energy rejected ERC1by clutch C1based on the temperature OIL1of the oil in which clutch C1operates. The temperature OIL1may affect the amount of energy rejected ERC1because the difference in temperature between the clutch C1and the oil in which it operates may affect how rapidly the clutch C1rejects energy to the oil. In some embodiments, propulsion-system controls19may use an equation similar to the following to estimate the amount of energy rejected ERC1by clutch C1during a given period of time:
ERC1=K6*(C1TEMPI−OIL1)*Δt

Where, C1TEMPIis the previously estimated initial temperature of clutch C1, OIL1is the temperature of the oil in which clutch C1operates, and K6is a constant related to the heat-transfer characteristics of the clutch C1and the oil in which it operates. Propulsion-system controls19may use similar approaches to estimate an amount of heat rejected by each of clutches C2, C3, and C4. Propulsion-system controls19may also use an air temperature value AIR, such as a sensed ambient air temperature, in evaluating an amount of heat rejected by a clutch C1, C2, C3, C4. Propulsion-system controls19may use the air temperature value AIR in combination with the oil temperature OIL1, OIL2, OIL3, OIL4to determine the amount of heat rejected by a clutch C1, C2, C3, C4. Alternatively, propulsion-system controls19may use the air temperature value AIR instead of the oil temperature value OIL1, OIL2, OIL3, OIL4. Propulsion-system controls19may do so, for example, in embodiments or circumstances where the oil temperature value OIL1, OIL2, OIL3, OIL4is not available to propulsion-system controls19.

With the estimated net energy absorbed by each clutch C1, C2, C3, and C4during the time period Δt, propulsion-system controls19may estimate the amount by which the temperature of each clutch C1, C2, C3, and C4increased during the time period Δt. For example, propulsion-system controls19may estimate the amount by which the temperature of clutch C1increased or decreased during the time period Δt by using the following equation:
ΔTEMPC1=K7*ENC1

Where, ΔTEMPC1is the change in temperature of clutch C1, K7is a constant related to the thermal properties of clutch C1, and ENC1is the estimated net energy absorbed by the clutch C1during the time period Δt. Propulsion-system controls19may use similar equations to determine the amount by which the temperature of each of clutches C2, C3, and C4changed during the time period Δt.

With the estimated initial temperatures and estimated changes in the temperatures of clutches C1, C2, C3, and C4over the time period Δt, propulsion-system controls19may estimate the temperature of each clutch at the end of the time period. For example, propulsion-system controls19may estimate the temperature of clutch C1at the end of the time period Δt using the following equation:
C1TEMP=C1TEMPI+ΔTEMPC1

Where C1TEMP is the estimated temperature of clutch C1at the end of the period Δt, C1TEMPIis the previously estimated initial temperature of clutch C1, and ATEMPC1is the estimated change in the temperature of clutch C1over the period Δt. Propulsion-system controls19may use similar equations to determine the temperature of each of clutches C2, C3, and C4at the end of the period Δt.

Propulsion-system controls19may periodically redetermine the temperatures of clutches C1, C2, C3, C4. After propulsion-system controls19have estimated the temperatures of the clutches C1, C2, C3, C4at the end of the first period Δt, propulsion-system controls19may redetermine the temperatures of clutches C1, C2, C3, C4periodically, such as after each additional increment of time equal to Δt. To do so, after estimating the temperatures of each of clutches C1, C2, C3, C4at the end of an interval Δt, propulsion-system controls19may reset the variables C1TEMPI, C2TEMPI, C3TEMPI, and C4TEMPIto be equal to the most recently estimated value of the temperatures C1TEMP, C2TEMP, C3TEMP, and C4TEMP, followed by repeating the process discussed above.

As they repeatedly redetermine the temperatures of clutches C1, C2, C3, C4, propulsion-system controls19may also redetermine the various other sensed and estimated values used in the process. For example, propulsion-system controls19may redetermine the value of oil temperatures OIL1, OIL2, OIL3, OIL4and the air temperature value AIR each time the clutch temperatures C1TEMP, C2TEMP, C3TEMP, and C4TEMP are redetermined. Tracking the actual values of these fluid temperatures and using them in the process of tracking the temperatures C1TEMP, C2TEMP, C3TEMP, and C4TEMP of clutches C1, C2, C3, and C4may enhance the accuracy of the estimated clutch temperatures.

Propulsion-system controls19may use the estimated temperatures C1TEMP, C2TEMP, C3TEMP, and C4TEMP of clutches C1, C2, C3, and C4in various ways. In some embodiments, propulsion-system controls19may monitor these values to detect if the temperature of any of clutches C1, C2, C3, and C4is approaching and/or has exceeded desirable levels. Propulsion-system controls19may store this information in memory for later access by individuals who may have an interest in knowing the temperature histories of clutches C1, C2, C3, and C4.

Additionally, in some embodiments, propulsion-system controls19may respond to an undesirably high value of the temperature C1TEMP, C2TEMP, C3TEMP, C4TEMP of a clutch C1, C2, C3, C4by taking measures to prevent additional heating of that clutch C1, C2, C3, C4. For example, if the estimated temperature C1TEMP, C2TEMP, C3TEMP, C4TEMP of a clutch C1, C2, C3, C4rises above a reference value corresponding to an undesirable thermal state (e.g., one in which component damage may occur), propulsion-system controls19may take action to reduce the amount of heat generated in that clutch C1, C2, C3, C4due to slippage. Propulsion-system controls19may do so by fully engaging the clutch C1, C2, C3, C4to substantially eliminate its slippage, at least partially disengaging the clutch C1, C2, C3, C4to reduce the amount of torque transmitted through it, or fully disengaging the clutch C1, C2, C3, C4to substantially cease any torque transmission through it. Propulsion-system controls19may select which of these clutch-protection strategies to employ for a given clutch C1, C2, C3, C4in a given set of circumstances based on various control algorithms.

In some embodiments, when the estimated temperature C1TEMP of clutch C1rises above a reference value indicative of an undesirable thermal condition, propulsion-system controls19may respond by fully engaging clutch C1to prevent slippage of clutch C1. By doing so, propulsion-system controls19may protect clutch C1while allowing full transmission of power to both the front traction devices16RF,16LF and the center and rear traction devices16RC,16LC,16RR,16LR. This may help propulsion system12provide power to any traction device16that has good traction on the terrain underlying mobile machine10. After fully engaging the clutch in response to the estimated temperature C1TEMP of clutch C1rising above a reference value, propulsion-system controls19may continue to reevaluate the estimated temperature C1TEMP. If the estimated temperature C1TEMP continues to rise an undesirable amount (such as above another reference temperature value) after being fully engaged, propulsion-system controls19may then fully disengage clutch C1to protect it.

The operation of propulsion system12and the manner in which propulsion-system controls19estimate and use the temperatures of clutches C1, C2, C3, and C4are not limited to the examples provided above. For instance, propulsion-system controls19may use different inputs and equations than discussed above to estimate the temperatures of clutches C1, C2, C3, and C4. For instance, in estimating the temperatures C1TEMP, C2TEMP, C3TEMP, C4TEMP of clutches C1, C2, C3, C4, propulsion-system controls19may use fluid temperatures other than the oil temperatures OIL1, OIL2, OIL3, OIL4and the air temperature AIR. The approach used by propulsion-system controls19to estimate the temperature of a clutch C1, C2, C3, C4may be simpler in one or more respects and/or more complicated in one or more respects. For example, in estimating the temperature of a given clutch C1, C2, C3, C4, propulsion-system controls19may factor in additional variables, such as the amount of heat generated and/or rejected by certain subcomponents of the clutch, in addition to or instead of the amount of heat generated and/or rejected by the clutch C1, C2, C3, C4to the oil within which the clutch operates. Similarly, propulsion-system controls19may estimate the temperatures of various subcomponents of each clutch C1, C2, C3, and C4, rather than just a general temperature for each clutch.