Apparatus for controlling drive forces of vehicle drive wheels connected by differential, by braking drive wheel having smaller critical drive force

An apparatus for controlling an actual value of a drive force produced between a road surface and each of four drive wheels consisting of a front right drive wheel, a front left drive wheel, a rear right drive wheel and a rear left drive wheel of a four-wheel drive motor vehicle including (a) a drive power source for driving said four drive wheels, (b) a front differential connecting said front right and left drive wheels so as to permit a difference between rotating speeds of said front right and left drive wheels, (c) a rear differential connecting said rear right and left drive wheels so as to permit a difference between rotating speeds of said rear right and left drive wheels, (d) a center differential connecting input shafts of said front and rear differentials so as to permit a difference between rotating speeds of said input shafts, and (e) four brakes for braking said four drive wheels, respectively, independently of each other, said center differential distributing a driving torque of said drive power source to said input shafts of said front and rear differentials, said front differential evenly distributing a torque received by the input shaft thereof to said front right and left drive wheels, for thereby producing the drive force between said road surface and each of said front right and left drive wheels, said rear differential evenly distributing a torque received by the input shaft thereof to said rear right and left drive wheels, for thereby producing the drive force between said road surface and each of said rear right and left drive wheels, said apparatus comprising:

• four wheel speed sensors for detecting the rotating speeds of said four drive wheels, respectively;
• and
• a brake control device responsive to output signals of said four wheel speed sensors, and operable when said four drive wheels have a first and a second drive wheel having different critical values of the drive force with respect to said road surface, the critical value of the drive force of said first drive wheel being smaller than that of said second drive wheel, said brake control device activating one of said four brakes which corresponds to said first drive wheel, to thereby apply a braking torque to said first drive wheel for increasing an apparent value of said drive force of said first drive wheel, in order to increase the actual value of the drive force of said second drive wheel, wherein said brake control device includes first control means for calculating a total speed control error for each of said front right and left drive wheels, and a total speed control error for each of said rear right and left drive wheels, said total speed control error for said each front drive wheel comprising a first error component which is a difference obtained by subtracting a half of an average speed of said rear right and left drive wheels from a half of an average speed of said front right and left drive wheels, and a second error component which is a difference obtained by subtracting said average speed of said front right and left drive wheels from the speed of said each front drive wheel, said total speed control error for said each rear drive wheel comprising a first error component which is a difference obtained by subtracting a half of an average speed of said front right and left drive wheels from a half of an average speed of said rear right and left drive wheels, and a second error component which is a difference obtained by subtracting said average speed of said rear right and left drive wheels from the speed of said each rear drive wheel, said first control means controlling each of said four brakes which corresponds to each of said four drive wheels whose total speed control error is a positive value, such that said positive total speed control error of said each drive wheel is substantially zeroed.