EMB ERJ 170/175 ER/LR
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance
Flight Crew Returned To Departure Airport
Aircraft; Software and Automation
Climbing out; Autopilot/Flight Director would indicate an overspeed and the plane would pitch up violently. Disconnected Autopilot and reestablish. 5 minutes later same thing. Happened 50-60 times during flight. Aircraft would not capture NAV. Flight Level Change (FLCH) would not engage. Could only fly in Heading (HDG) mode and Flight Path Angle (FPA). FADEC never shifted from TO mode with the Automatic Takeoff Thrust Control System (ATTCS) armed. Checked Emergency Procedure Checklist (EPC) but could not find a checklist that would pertain to us. Decided to return to ZZZ. At decision time it indicated we would be 3000 lbs over landing weight so we initiated procedures to minimize overweight landing and returned to ZZZ. Landed approximately 750lbs over weight. Aircraft landed fine and there were no additional issues. Upon return I wrote the airplane up. Priority handling was not requested as the aircraft was still controllable with no Autopilot or Flight Director.
EMB-175 Captain reported malfunctioning autoflight system which resulted in a return to departure airport.