Drive force distribution device and method for distributing drive force

1. A drive force distribution device of a vehicle including a main drive wheel, a sub drive wheel, and a drive force transmission system that transmits a drive force generated by a drive source to the drive wheels, the device comprising:

a coupling arranged in the drive force transmission system, wherein the coupling changes a torque transmission rate of a torque transmitted from an input of the coupling to an output of the coupling, thereby varying a drive force distribution ratio between the main drive wheel and the sub drive wheel; and

a control section that controls operation of the coupling, the control section estimating a temperature of at least one of heat generating portions of the drive force transmission system by calculating a value related to the heat energy accumulated in the at least one of the heat generating portions during torque transmission through the heat generating portion in correspondence with a rotational speed of the at least one of the heat generating portions and the torque transmission rate in the at least one of the heat generating portions, and correcting the calculated value by a correction value related to an outside temperature, wherein, if the estimated temperature exceeds a predetermined temperature, the control section controls the operation of the coupling to suppress overheating of the heat generating portion.

2. The device according to claim 1 , wherein:

the heat generating portions include at least one of a differential and a transfer case, the differential being arranged between the coupling and the sub drive wheel, the transfer case being provided between the drive source and the coupling and between the drive source and the main drive wheel; and the control section controls the operation of the coupling to decrease the torque transmission rate if the estimated temperature exceeds the predetermined temperature.

3. The device according to claim 1 , wherein:

the heat generating portions include the coupling; and

if the estimated temperature of the coupling exceeds the predetermined temperature, the control section controls the operation of the coupling to decrease at least one of a differential rotational speed between the input and the output and the torque transmission rate.

4. The device according to claim 3 , wherein:

if the estimated temperature of the coupling exceeds the predetermined temperature, the control section controls the operation of the coupling to maximize the torque transmission rate.

5. A method for distributing drive force of a vehicle including a main drive wheel, a sub drive wheel, and a drive force transmission system that transmits a drive force generated by a drive source to the drive wheels, the method comprising:

controlling operation of a coupling arranged in the drive force transmission system to vary a drive force distribution ratio between the main drive wheel and the sub drive wheel by changing a torque transmission rate of a torque transmitted from an input of the coupling to an output of the coupling;

estimating a temperature of at least one of heat generating portions of the drive force transmission system by calculating a value related to the heat energy accumulated in the at least one of the heat generating portions during torque transmission through the heat generating portion in correspondence with the rotational speed of the at least one of the heat generating portions and the torque transmission rate in the at least one of the heat generating portions, and correcting the calculated value by a correction value related to an outside temperature;

determining whether the estimated temperature of at least one of the heat generating portions exceeds a corresponding predetermined temperature; and

controlling the operation of the coupling to suppress overheating of the corresponding heat generating portion if the estimated temperature exceeds the predetermined temperature.

6. The method according to claim 5 , further comprising:

estimating a temperature of at least one of a differential and a transfer case as the heat generating portion, the differential being arranged between the coupling and the sub drive wheel, the transfer case being provided between the drive source and the coupling and between the drive source and the main drive wheel; and

controlling the operation of the coupling to decrease the torque transmission rate if the estimated temperature exceeds the predetermined temperature.

7. The method according to claim 5 , further comprising:

estimating the temperature of the coupling as the heat generating portion; and

controlling the operation of the coupling to decrease at least one of a differential rotational speed between the input and the output and the torque transmission rate if the estimated temperature exceeds the predetermined temperature of the coupling.

8. The method according to claim 7 , further comprising:

controlling the operation of the coupling to maximize the torque transmission rate if the estimated temperature of the coupling exceeds the predetermined temperature.

9. A drive force distribution device of a vehicle including a main drive wheel, a sub drive wheel, and a drive force transmission system that transmits a drive force generated by a drive source to the drive wheels, the device comprising:

a coupling arranged in the drive force transmission system, wherein the coupling changes a torque transmission rate of a torque transmitted from an input of the coupling to an output of the coupling, thereby varying a drive force distribution ratio between the main drive wheel and the sub drive wheel; and

a control section that controls operation of the coupling, the control section estimating a temperature of at least one of heat generating portions of the drive force transmission system in correspondence with a rotational speed of the heat generating portion, the torque transmission rate, and an outside temperature, wherein, is the estimated temperature exceeds a predetermined temperature, the control section controls the operation of the coupling to suppress overheating of the heat generating portion, and wherein the heat generating portions include the coupling;

if the estimated temperature of the coupling exceeds the predetermined temperature and an estimated temperature of at least one of the heat generating portions other than the coupling exceeds a respective predetermined temperature, the control section controls the operation of the coupling to minimize the torque transmission rate.

10. A method for distributing drive force of a vehicle including a main drive wheel, a sub drive wheel, and a drive force transmission system that transmits a drive force generated by a drive source to the drive wheels, the method comprising:

controlling operation of a coupling arranged in the drive force transmission system to vary a drive force distribution ratio between the main drive wheel and the sub drive wheel by changing a torque transmission rate of a torque transmitted from an input of the coupling to an output of the coupling;

estimating a temperature of at least one of heat generating portions of the drive force transmission system in correspondence with the rotational speed of the heat generating portion, the torque transmission rate, and an outside temperature;

determining whether the estimated temperature of at least one of the heat generating portions exceeds a corresponding predetermined temperature;

controlling the operation of the coupling to suppress overheating of the corresponding heat generating portion if the estimated temperature exceeds the predetermined temperature; and estimating the temperature of the coupling as the heat generating portion;

controlling the operation of the coupling to minimize the torque transmission rate if the estimated temperature of the coupling exceeds the predetermined temperature and an estimated temperature of at least one of the heat generating portions other than the coupling exceeds a respective predetermined temperature.