Design and Test of a New Type of Overrunning Clutch

Abstract

The overrunning clutch, or freewheel, is a kind of universal part with a one-way drive character, and is widely used in machinery. Typical roller overrunning clutches and sprag overrunning clutches have shortcomings such as low load bearing capacity, low torsional stiffness, and short life. For these reasons, studies on high-performance overrunning clutches have always been the focus of researchers. In this paper, a new type of double arc sprag overrunning clutch is proposed that overcomes the disadvantages of poor transmission capacity and low rigidity found in traditional overrunning clutches. The mechanical model of the double arc sprag overrunning clutch is established, the calculation formulas of the overrunning clutch engagement conditions and overrunning conditions are deduced, and the forces of the outer ring, roller, and inner star wheel of the overrunning clutch are also deduced. The contact stress and transmission torque of the overrunning clutch are compared with those of the roller overrunning clutch and the sprag overrunning clutch. The results show that the proposed overrunning clutch has the largest load capacity, which is 5.75 times that of the roller type overrunning clutch, and 2.1 times that of the sprag type overrunning clutch. The experiment shows that the proposed overrunning clutch has reliable bonding conditions in the oil-free and oil-immersed state, and the overrunning condition is sensitive, which indicates the effectiveness of the double arc sprag overrunning clutch. The roller overrunning clutch and double arc sprag overrunning clutch with the same geometric parameters are designed and manufactured, and the torsional stiffness test of the three types of overrunning clutches is carried out. The results show that the torsional stiffness of the double arc sprag overrunning clutch is the largest, which is 4.6 times of the roller overrunning clutch and 6.2 times of the sprag overrunning clutch.