Drill motor gearbox lock mechanism

[golf_cart_john]

The Bosch drill motor gearboxes have a mechanism that is making me curious, and I'd like to use it on a robot. This mechanism allows the main axle to free-spin during normal operation, but locks up the shaft when the motor stops powering. My team has removed some critical pieces of this mechanism (cause we don't want the robots to drive like that), but I've never figured out how it works. Does anybody know how this works? I could use some diagrams, or good explainations. The other question is, does anybody know if there are Intellectual Property/Patent issues if I copy this mechanism for a robot?