Hydraulic synchronizer

A hydraulic synchronizer for selectively coupling first and second gears to a drive shaft that is rotatable about a rotation axis, the synchronizer comprising:

• a shaft hub configured to be rotated with the drive shaft, the shaft hub having first and second splined annuli and at least one fluid passage;
• first and second rings each disposed about the shaft hub and movable along the rotation axis with respect to the shaft hub;
• first and second shift collars fixedly coupled to the associated first and second rings, the first and second shift collars each having a splined annulus engaged with the associated first and second splined annuli of the shaft hub, the associated first and second shift collars being configured to engage splines of the associated first and second gears when the associated first and second rings are in the associated first and second axial positions and to be disengaged from the splines of the associated first and second gears when the associated first and second rings are in associated first and second neutral positions, the first and second shift collars being configured to transmit rotational input from the shaft hub to the associated first and second gears when the associated first and second rings are in the associated first and second axial positions;
• and
• a plurality of hydraulic chambers configured to receive hydraulic fluid from the at least one fluid passage and configured to move the first and second rings to the associated first and second axial positions and the associated neutral positions;
• wherein hydraulic pressure in a first of the hydraulic chambers acts on the first ring to move the first ring to the first axial position and hydraulic pressure in a second of the hydraulic chambers acts on the first ring to move the first ring to the first neutral position.