Finishing trowel pitch control and clutch system

Abstract

An automatic, self locking clutch system effectuates blade pitch control on concrete finishing trowels. The clutch instantly releases upon the touch of the operator. A trowel has a downwardly projecting, motor-driven rotor comprising a plurality of radially spaced apart finishing blades directly contacting the concrete surface. A handle extends from a rigid frame and terminates in handlebars grasped by an operator. Control arms extend from the blades into contact with a plate to vary pitch by conventionally rotating the blades about their longitudinal axis. A clutch operatively interconnects a lever and a linkage extending to the swash plate. The clutch comprises a tubular housing coaxially receiving a drive shaft that rotatably controls an internal rotor. A set of spring biased, cylindrical rollers are confined within channels defined in the rotor between major and minor lobes thereof. The rollers are contacted by locking ledge portions of the channels and jammed into frictional engagement with the inner walls of the housing. The rollers thus wedgably lock the shaft to prevent rotation. A clutch actuator is coaxially fitted within the housing and driven by the lever for selectively unlocking the rollers and rotating the shaft to displace the linkage and establish the desired blade pitch. The shaft mounts an eccentric sprocket that directly drives a roller chain portion of the linkage. The eccentric sprocket provides an initial mechanical advantage, so trowel blade pitch is first finely adjusted, and as blade angle increases, lever response is coarser.