Inching clutch compensation for centrifugal effects

In a transmission having a plurality of clutches for transferring torque from an input shaft to an output shaft at a selected one of a plurality of gear speed ratios, at least one of said clutches being a hydraulic clutch including a piston in a rotating piston cavity for applying pressure to clutch plates, the piston being responsive to the pressure of hydraulic fluid injected into the cavity on one side of said piston at a pressure determined by a clutch actuation signal, a method of compensating for the pressure applied to the clutch plates as a result of centrifugal force exerted on hydraulic fluid in the cavity, said method comprising the steps of:

• for said at least one hydraulic clutch, providing a corresponding table of compensation values which, when used to modify the actuation signal applied to the corresponding clutch, causes a reduction in the pressure applied to the corresponding clutch by an amount substantially equal to a pressure applied to the clutch plates as a result of centrifugal force exerted on hydraulic fluid in the piston cavity of the corresponding clutch on one side of said piston;
• determining the rate of rotation of the piston cavity of an active hydraulic clutch to which a clutch actuation signal is to be applied;
• selecting a compensation value from the table corresponding to the active clutch in accordance with the determined rate of rotation of the piston cavity of the active clutch;
• and,
• modifying the actuation signal applied to the active clutch in accordance with the compensation value read from the table so that the torque transmitted through said one of said hydraulic clutches is unaffected by the centrifugal pressures exerted on the hydraulic fluid during rotation thereof, thereby permitting consistent control of the transmission of torque through said clutch irrespective of the rate of rotation of the piston cavity.

In a transmission system, the combination comprising:

• a transmission having a plurality of hydraulic clutches for selectively transferring torque from a rotatable drive member to a rotatable driven member, at least two of said clutches being inching clutches;
• gear selection means for selectively engaging said plurality of clutches so that an output shaft of the transmission may be driven at a selected gear speed ratio relative to an input shaft;
• an operator-controlled clutch pedal;
• control means responsive to said clutch pedal for deriving a modulation signal for modulating a clutch actuation signal;
• said inching clutches each having a clutch piston positioned within a cavity which rotates with one of said members,
• said cavities containing hydraulic fluid on one side of said piston which is subjected to centrifugal force as the cavity rotates, thereby applying a force to said pistons;
• said control means including means for storing compensation values for compensating for the effects of said centrifugal pressures on said pistons;
• and
• sensor means for sensing the rate of rotation of said input shaft,
• said control means including means responsive to said sensing means and said gear selection means for modifying the clutch actuation signal applied to one of said inching clutches with one of said stored values so that the torque transmitted through said one of said inching clutches is unaffected by the centrifugal pressures exerted on the hydraulic fluid during rotation thereof, thereby permitting the operator to have consistent control of the transmission of torque through said clutch irrespective of the rate of rotation of said input shaft.