BÀI GIẢNG TRANG TRÍ hệ ĐỘNG lực CHƯƠNG 3(ENGLISH)

CHAPTER 3: MODE OF DRIVING AND DRIVING MECHANISMS IN THIS CHAPTER WE HAVE THE FOLLOWING UNITS: UNIT 3.1: FUNCTION AND CLASSIFICATION UNIT 3.2: DIRECT DRIVING MODE UNIT 3.3: INDIRECT DRIVING MODE UNIT 3.4: SPECIAL DRIVING MODE UNIT 3.5: HYDRAULIC DRVING EQUIPMENT UNIT 3.6: FRICTION CLUTCH UNIT 3.7: REDUCTION GEAR UNIT 3.1: FUNCTION AND CLASSIFICATION Driving equipment and its function   Driving equipment is used to transmit power from the main engine to the propeller Driving equipment consist of: - Shafting: Intermediate shaft, thrust shaft and propeller shaft - Bearings: Intermediate bearings, thrust bearing and stern bearings - Shaft coupling - Clutch, reduction gear (intermediate equipment) - Electric transmission equipment Classification  Today, there are three kinds of driving modes for ships They are: - Direct driving mode - Indirect driving mode - Special driving mode UNIT 3.2: DIRECT DRIVING MODE ME FPP PROPELLER FACTORY Feature ♥ ♥ ♥ ♥ There is not any intermediate equipment between the main engine and the propeller Direct driving is carried out only by the shafting Revolution of the propeller is the same the main engine revolution It is commonly applied on the large and medium-sized ships when revolution of the main engine is about 85 ÷ 300 rpm In a direct driving propulsion plant, the main engine is a kind of low-speed, large power, direct reversing diesel engine The most common is low-speed; two- strokes cycle diesel engine with crosshead Advantages ♪ Driving efficiency is high It does not have any loss other than friction loss in the bearings A direct driving propulsion plant with short shafting will have a driving efficiency of about 97 - 98% ♪ The main engine has low specific fuel consumption ♪ The propeller efficiency is high (because revolution of the main engine is the same as the optimum range of the propeller revolution) ♪ Its structure is simple and easy to maintain It is safe in working, reduce noise and vibration and has high longevity Disadvantages ♪ The main engine has large dimensions and weight so dimensions and weight of the propulsion plant are increased, transportation ability of the ship is reduced The direct driving mode is not suitable for ships with small displacement, or height of the engine room is limited ♪ To reverse direction of the propeller, the main engine must be reversed so it is not flexible ♪ The direct driving mode is suitable for tanker ships, general cargo ships UNIT 3.3: INDIRECT DRIVING MODE Clutch Gear-box ME Figure 1.16 ME driving a propeller through gear-box Advantages     Dimension and weight of the propulsion plant are small It reduces dimensions of the engine room and increases the cargo transportation ability of the ship At the same power, the weight of the high or medium-speed diesel engine is 40% lighter than a low-speed diesel engine The same type of diesel engine can be used for many kinds of ships that have different propeller revolution rates It is not necessary to directly reverse the main engine for reversing direction of the ship This can be done by the multi-stage reduction gear therefore, the flexibility of the propulsion plant and the longevity of the main engine will be increased Two or more main engines can be used to drive only one propeller, thus increases the flexibility of the propulsion plant and the main engines can be effectively operated in every operating condition (even when light load) Disadvantages  Transmission efficiency is lower than the direct driving  It is complex and difficult to operate, maintain and repair  Longevity is shorter  The indirect driving mode is more suitable for naval ships, passenger ships and container ships Rmin Rmax In fact, to reduce dimension and increase torque transmission ability, a multiple-disk friction clutch is used Figure 3.7: Multiple-disk friction clutch b Material for the friction clutch Material for manufacturing the friction clutch has to meet the following requirements: - Abrasion resistance ability is high - Friction coefficient is high and not depends on temperature - Friction surfaces must not be stuck to each other at high temperature - Longevity must be high - It will not be deformed due to heat - Heat conductibility is high Main materials: Cast iron and steel (most commons), brass, asbestos, leather, and wood Cone friction clutch a Principle α Q 1- Actuating shaft 2- Receiving shaft Metal friction surface couple Metal-leather surface couple Steel-wood surface couple 3- Actuating friction cone 4- Receiving friction cone α = ÷ 10o α = 12 ÷ 13o α ≥ 20o The cone friction clutch consists of friction cones (3) and (4), which are installed on shafts (1) and (2) The actuating shaft (1) is connected to the crankshaft; the receiving shaft is connected to the propeller shaft The friction cone (3) is fixed on the shaft (1), the friction cone (4) can be freely slid along the shaft (2) The cone friction clutch and the disk friction clutch have the same principle In case of the cone friction clutch, average radius of the friction cone can be determined by the shaft diameter: Rtb = (3 ÷ 5)d When designing, the angle α of the friction cone surfaces must be suitably calculated so that the friction cone surfaces can be released when stopping the axial thrust force Q The angle α depends on friction material: b Features of the cone friction clutch - In comparison with the same diameter disk friction clutch, the axial thrust force of the cone friction clutch is only equal to 2/3 when the same transmission torque - Dimensions of the friction cones are large so the cone friction clutch is unwieldy - In comparison with the multiple-disk friction clutch, the relative slip of the cone friction clutch is higher so it is less stable - It is complicated to manufacture - It must be accurately balanced when it has a large dimension and high speed Air-actuated friction clutch a Principle 1- Actuating shaft 2- Receiving shaft 3- Outside drum 4- Inside drum 5- Inner tuber 6- Steel cover 7- Friction surface  The air-actuated friction clutch consists of two cylinder drums (3)- actuating drum and (4)- receiving drum, which are fixed on shaft (1) and (2) Shaft (1) is connected to the crankshaft of the main engine Shaft (2) is connected to the propeller shaft The inner tube (5) is placed in the steel cover (6), which is located between drums (3) and (4) Inside of the steel cover is provided with friction surface (7) Outside of the steel cover is secured on the outside drum  When the main engine is working, the outside drum (3) is turned with shaft (1) Supplying compressed air into the inner tube, the steel cover with friction surface will be pressed on the surface of the inside drum due to pressure of the compressed air  By action of the friction force, torque is transmitted from the actuating shaft to the receiving shaft Revolution of the receiving shaft is gradually increased to the actuating shaft revolution  When the compressed air is drained, the air-actuated friction clutch is in unloading state b Features of the air-actuated friction clutch - When working, it can center itself - Transmission torque of the air-actuated friction clutch depends on pressure of the compressed air When air pressure increased, the relative slip reduces then revolution of the receiving shaft will increase However, centrifugal force also increases therefore transmission torque a little decrease So transmission torque is not proportional with the air pressure Suitable pressure is about ÷ 10 (KG/cm2) - Noise and vibration can be decreased - It is complex in the structure c Notices - Suitable working range of temperature is about (- 30 ÷ 50)oC - It must be accurately balanced especially when working at high revolution - It must be replaced when friction surfaces worn excessively UNIT 3.7 REDUCTION GEAR Principle (Figure 3.10) A simple reduction gear consists of the sun gear (1), which is fixed on the crankshaft It works as a driving gear The internal gearing pinion (2) is fixed (fixed center gear), the planet pinion (3) has a mobile shaft and the connecting rod (planet carrier) (4) is connected to the propeller shaft In this gear-transmission, the planet pinion (3) takes part in two movements at the same time: It turns around the planet carrier (4) and moves relatively to the sun gear (1) and the internal gearing pinion (2) Transmission ratio of the reduction gear:: n1 i = n2 Where: - n1 revolution of the main engine - n2 revolution of the propeller Figure 3.10: Reduction gear n2 n1 ME 1- Sun gear (center gear) 3- Planet pinion 2- Internal gearing pinion 4- Planet carrier (connecting rod) Advantages - Its structure is simple; dimensions and weight are small - It is safe for operating - Transmission efficiency is high (98 ÷ 99%) Multiple-stage reduction gear When the transmission ratio is high, its dimensions are too large, if a single-stage reduction gear is used In that case, a multiple-stage reduction gear is used 10 n2 n1 1,5- First and second stage sun gears 2,6- First and second stage internal gearing pinions 3,7- First and second stage planet pinions 4,8- First and second stage planet carriers 9,10- Brakes The reversible two-stage reduction gear consists of: the fist stage sun gear (1) is connected to the crankshaft (with revolution n1) The first stage internal gearing pinion (2) is connected to the second stage sun gear (5) The second stage internal gearing pinion (6) is connected to the first stage planet carriers (4) The second stage planet carrier (8) is connected to the propeller shaft (with revolution n2) Each stage has planet pinions (3) and (7) The brakes (9) and (10) are used to carry out the reversing direction of the propeller Ahead:  z  z1  i = iI iII = 1 − 1 −   z1  z  Astern: i = i I i II  z2 = 1 − z   z2  z  Finish chapter   QUESTION 1: QUESTION 2: