lesson 18　Steering gear 轮机英语课件.ppt

Lesson 18 Steering gear (舵机、操舵装置) The steering gear is one of the most important services in the ship and its main function is to control the ship’s course. There are four main types of steering gears employed for power operation of the rudder(舵叶), (i) the steam steering gear, (ii) the hydraulic steering gear, (iii) the electric steering gear and (iv) the electro-hydraulic steering gear. The total system may be considered made up of three parts: control equipment, a power unit and a transmission to the rudder stock(舵杆). The first part conveys(传递) a signal or desired rudder angle from the bridge (wheel house). The second one provides the force, when required, to move the rudder to that angle. The third is the means by which the movement of the rudder is accomplished. According to the way the steering gear is operated, the steering gear may be divided into three kinds: hand-steering, followup (随动) steering and automatic steering. The electro-hydraulic gear is now the most widely applied. A two ram(撞杆) hydraulic gear consists of a hydraulic ram situated on the port side of the tiller(舵柄) and another ram on the starboard side, linked at their outer ends to the tiller arm by a crosshead and swivel block(转动滑块), the other ends of the rams working inside their own hydraulic cylinders and pipes connect these cylinders to a hydraulic pump. The tiller is firmly keyed to the rudder stock. The pump is of special construction and may be axial or radial design. The pump runs continuously in the same direction driven by an electric motor, and the position of a movable plate or a floating ring inside the pump controls the suction and discharge of the oil. When the plate or ring is in mid position, no oil is drawn; when the plate or ring is moved in one direction from mid position, oil is drawn from one cylinder and discharged into the other; when the plate or ring is moved in the opposite direction, the suction and discharge of the oil is reversed in direction. The pl