tailieunhanh - Clutches and Brakes Design and Selection P09

Công nghệ cơ khí hay kỹ thuật cơ khí là ngành ứng dụng các nguyên lý vật lý để tạo ra các loại máy móc và thiết bị hoặc các vật dụng hữu ích. Cơ khí áp dụng các nguyên lý nhiệt động lực học, định luật bảo toàn khối lượng và năng lượng để phân tích các hệ vật lý tĩnh và động, phục vụ cho công tác thiết kế trong các lĩnh vực như ô tô, máy bay và các phương tiện giao thông khác, các hệ thống gia nhiệt và làm lạnh, đồ dùng gia đình, máy. | 9 Centrifugal One-Way and Detent Clutches These are special-purpose clutches that are used in automatic transmissions in devices for bringing high-speed machinery up to speed in chain saws in conveyor drives and in similar industrial vehicular and large- and smallequipment applications. The centrifugal clutches provide a speed-dependent torque which acts only when the rotational speed exceeds a particular value the one-way or overrunning clutches provide a torque that is not speed dependent once they are engaged but is dependent on the direction of rotation and the detent clutches provide a torque that cannot exceed a prescribed value. I. CENTRIFUGAL CLUTCHES A centrifugal clutch may be described as consisting of an inner cylinder that is attached to the input shaft and an outer housing that is attached to the output shaft as in Figure 1. Sectors of the inner cylinder are cut out to allow it to be fitted with weights that can slide radially outward as the inner cylinder rotates so that the weights are forced against the outer housing by centrifugal force and thereby transmit torque to the outer housing. Centrifugal clutches designed for lower power transfer may use simpler designs. In some chain saws for example it is the weights themselves that are recessed to accept radial guides from the central shaft. Copyright 2004 Marcel Dekker Inc. Figure 1 Centrifugal clutch. Courtesy Dana Corp. Inc. Toledo OH. Because of the variety of centrifugal clutch designs their analysis will be described in general terms. Let A denote the cross-sectional area of each weight in a plane perpendicular to the axis of rotation written in the form of an annular sector of angle f o as A cforo2 1 - h2 1-1 where h r ro. Parameters h and c are factors that may be used to express other cross-sectional areas in thisform of equation 1-1 . When h 0 c 1 2 and f o 2k area A in equation 1-1 becomes that of a disc of radius ro. Let w denote the width of each weight measured in a direction parallel to