Mechanical clutch unit

The present invention provides clutch systems for the control of the transmission of torque to the front (or rear) wheels of a vehicle (e.g., an ATV), thus being operable to change the vehicle from a two-wheel, rear-drive (or front-drive) vehicle to a four wheel drive vehicle by engaging the clutch systems thereof. The clutch system is contained within an extended portion of a housing that also contains a differential system, thus eliminating the need for fastening a separate clutch system housing to the differential housing. The clutch system is actuated by energizing a coil which in turn causes tab members of an actuation disk to disengage from notches formed on an inner race, allowing the actuation of a roller clutch system. When the coil is de-energized, the actuation disk engages the inner race and prevents inadvertent or undesired actuation of the clutch system.