Academic literature on the topic 'Over-running ratchet'

Compliance criteria are used to evaluate the general class of over-running clutches to determine which type is best suited to benefit from compliance. The criteria used in the evaluation include the presence and angle of rotation of revolute joints, the possibility for part count reduction, the presence of springs, possible reduction in weight, and the method of clutch engagement. Sprag, spring, roller or ball, and ratchet and pawl clutch types were evaluated, and the ratchet and pawl type of over-running clutch was demonstrated to be the most promising. Within this type of over-running clutch, different designs incorporating bending, tension, and compression loading of the pawls were explored to determine the best method for loading the pawls. The clutches were compared using the maximum output torque. It was determined that the clutch incorporating rigid pawls loaded in compression produced the largest output torque. The maximum output torque for this clutch was measured at 65.6 N-m.

This thesis proposes that compliant mechanism theory can be used to design over-running ratchet and pawl clutches with reduced part count, lower assembly and manufacturing time while maintaining functionality. An extension of the theory to the micro regime is also briefly addressed. The results of the research show that the ratchet and pawl type of over-running clutch is a good choice for the use of compliance, and the clutch pawls should be loaded in compression to get the largest amount of output torque. It was found that com-pliant mechanism theory can be used to design ratchet and pawl clutches with fewer parts and lower manufacturing and assembly costs, and that these clutches perform comparable to traditional rigid-body ratchet and pawl clutches. Compliant ratchet and pawl clutches can replace traditional rigid-body clutches in some applications and now make it possible to be used in applications where it was once not economically feasible to use a over-running clutch. It was also found that these clutches function at the micro level.

Abstract A new compliant, over-running ratchet and pawl clutch with centrifugal throw-out has been developed that drastically reduces the overall part count as compared to traditional ratchet and pawl clutches. Part count for the pawl hub assembly was virtually eliminated by making the hub a single compliant mechanism. This results in large savings in manufacturing, assembly and maintenance costs. Peak torque output for a polypropylene clutch was measured at over 66.2 N-m with an over-running torque measured at < 0.01 N-m. A mathematical model has been developed to predict the rotational speed at which the pawls disengage from the ratchet when free-wheeling. This model was verified experimentally to be accurate within 5.2%. This clutch also demonstrates the advantage of compliant mechanisms to reduce assembly and manufacturing costs.

Abstract Compliance criteria is used to evaluate the general class of over-running clutches to determine which type is best suited to benefit from compliance. The criteria used in the evaluation include the presence and amount of revolution of revolute joints, the possibility for part count reduction, the presence of springs, possible reduction in weight, and the method of clutch engagement. The ratchet and pawl type of over-running clutch was shown to be the most promising. Within this type of over-running clutch, different designs incorporating bending, tension, and compression loading of the pawls were explored to determine the best method for loading the pawls. The clutches were compared using a ratio of the maximum output torque to over-running torque. It was determined that the clutch incorporating rigid pawls loaded in compression produced the largest ratio of output torque to over-running torque. The maximum output torque for this clutch was measured at 65.6 N-m and the over-running torque was measured at 0.011 N-m yielding a ratio of 5964.