When regulators sleep and auto companies place profits over safety, safety defects pile up. A record number of vehicles — more than 50 million — have been recalled this year, a result of congressional hearings and Justice Department prosecutions, which exposed a mass of deadly defects that the auto industry had concealed. From the Ford Explorer rollovers in the 1990s and Toyotas’ issue with unintended acceleration in the 2000s to the recent fatal consequences of defective General Motors ignition switches and Takata airbags, the auto companies hid defects to avoid recalls and save money.