A Bendix drive is a type of engagement mechanism used in starter motors of

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...

s. The device allows the pinion gear of the starter motor to engage or disengage the

ring gear An epicyclic gear train (also known as a planetary gearset) consists of two gears mounted so that the center of one gear revolves around the center of the other. A carrier connects the centers of the two gears and rotates the planet and sun gea ...

(which is attached to the

flywheel A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, assu ...

flexplate A flexplate (or flex plate) is a metal disk that connects the output from an engine to the input of a torque converter in a car equipped with an automatic transmission. It takes the place of the flywheel found in a conventional manual transmiss ...

of the engine) automatically when the starter is powered or when the engine fires, respectively. It is named after its inventor, Vincent Hugo Bendix.

Operation

The Bendix system places the starter drive pinion on a helical drive spring. When the starter motor begins turning, the inertia of the drive pinion assembly causes it to wind the spring forcing the length of the spring to change, and allowing the pinion to engage with the

. When the engine starts, backdrive from the ring gear causes the drive pinion to exceed the rotative speed of the starter, at which point the drive pinion is forced back and out of mesh with the ring gear. The main drawback to the Bendix drive is that it relies on a certain amount of "clash" between the teeth of the pinion and the ring gears before they slip into place and mate completely; the teeth of the pinion are already spinning when they come into contact with the static ring gear, and unless they happen to align perfectly at the moment they engage, the pinion teeth will strike the teeth of the ring gear side-to-side rather than face-to-face, and continue to rotate until both align. This increases wear on both sets of teeth. For this reason the Bendix drive has been largely superseded in starter motor design by the pre-engagement system using a

starter solenoid A starter solenoid is an electromagnet which is actuated to engage the starter motor of an internal combustion engine. It is normally attached directly to the starter motor which it controls. Its primary function is as the actuating coil of a co ...

References

* * * Internal combustion engine Engines Bendix Corporation {{Bendix