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 DRIVI

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

1 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

2 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

1 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.

2 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

3 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

UNIT 3.3: INDIRECT DRIVING MODE

Clutch Gear-box

Figure 1.16 ME driving a propeller through gear-box

ME

2 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)

3 Disadvantages

 Transmission efficiency is lower than the direct driving

 It is complex and difficult to operate, maintain and repair

 The indirect driving mode is more suitable for naval ships, passenger ships and container ships

UNIT 3.4: SPECIAL DRIVING MODE

I Electric driving.

1 Feature

 - There is no mechanical connection between the main engine and the propeller.

 - There are two times of energy transformation.

Figure: Schematic of Electric transmission propulsion plant

(ETPP)

M/E Gen Motor

2 Advantages

- The same as the indirect driving mode, the main engine is usually a high or medium-speed therefore, the dimension and weight of the propulsion plant is small and thus reduces the dimensions of the engine room

- It is not necessary to reverse the main engine when reversing the direction of the ship This can be carried out by reversing the direction of the electric motor Therefore the longevity of the main engine and the flexibility of the propulsion plant will be increased

- Revolution of the propeller can be changed while the main engine is still working

at a constant speed This can be done by changing revolution of the motor Therefore the main engine can always be run at the most economic region

- It is not necessary to have a long shafting and many intermediate bearings, so the main engine can be located in the best suitable position in the engine room

- When the ship is stably sailing on the sea, the main generator can satisfy a part of the electric energy requirements of the ship

3 Disadvantages

- Transmission efficiency is much lower than the two kinds listed above

- Overload ability of the electric motor is less

- It is complex, not economic and expensive

- Longevity is shorter

- Electric driving mode is more suitable for naval ships, fishing ships

4 Electric driving diagram

 This is the simplest illustration of the direct current electric driving propulsion plant.

ME G

2- Excited coil of the motor

3- Excited coil of the generator

4- Generator 5- Main engine 6- Rheostat

II CONTROLABLE PITCH PROPELLER DRIVING

1 Structure and methods for controlling pitch of the propeller.

a Structure

It consists of two main parts:

- Blades can be turned around their axis

- Mechanism for controlling pitch of the propeller This

mechanism is generally installed inside the propeller hub.

b Methods for controlling pitch of the propeller

To vary pitch of the propeller, its blades must be turned around their vertical axis This movement is carried out by hydraulic or mechanical means Today, there are four common methods to control pitch of the

propeller; the illustrations are showed as below:

3 4

2 1

Figure 3.2: Methods for controlling pitch of the propeller

1- Gearing type 2- Turning type

3- Connecting rod type 4- Rack-and-pinion type

2 Advantages

 It is not necessary to change the rotating direction and revolution of the main engine when reversing the direction and changing speed of the ship This can be done by controlling the pitch of the propeller

 The main engine is permitted to operate effectively even in heavy condition and

is protected from overload

 Flexibility and longevity of the propulsion plant are high

3 Disadvantage

• Mechanisms are complex The quality sealing of the propeller hub is required Therefore, it is very difficult to manufacture, assemble and repair It is expensive

• It is difficult to operate, especially determining the suitable working point between

the main engine and the propeller

• If the pitch ratio (H/D) and the propeller revolution (np) are selected unsuitably,

the result power of the main engine is reduced

• Knowledge of the operator is required.

• Controllable-pitch propeller driving becomes more suitable for use on naval ships,

passenger ships, and workshop ships, fishing ships, rescue ships

UNIT 3.5 HYDRAULIC DRIVING EQUIPMENT

I PRINCIPLE AND APPLICATION

1 Principle of hydraulic driving equipment

2 1

2 Features and application of hydraulic driving equipment

 - Clutch and unclutch crankshaft of the main engine and the propeller shaft.

 - Extend working region of the propulsion plant The main engine will not be overloaded in rough sea conditions.

 - It permits a centering error between the crankshaft and the propeller shaft.

 - Reversible hydraulic driving equipment can be used.

 - Hydraulic-driving equipment is applied in the propulsion plant

as a hydraulic clutch or a hydraulic speed reducer.

II HYDRAULIC DRIVING EQUIPMENT

1 Hydraulic clutch

a Features

- When the hydraulic clutch is working stably, torque on the receiving shaft is not changed

- Centrifugal pump and hydraulic turbine have the same dimension

- High transmission efficiency

b Principle of the hydraulic clutch

 c Transmission efficiency of the hydraulic clutch

2 Hydraulic speed reducer

3 6

2 5

1

4

1- Centrifugal pump 4- Pump shaft (actuating shaft) 2- Hydraulic turbine 5- Turbine shaft (receiving shaft) 3- Nozzle 6- Cover

b Principle of the hydraulic speed reducer

UNIT 3.6: FRICTION CLUTCH

I Features of Friction clutch

 Structure is simple, weight and dimensions are small.

 Energy loss is small, transmission efficiency is high.

 Transition stage is short (unstable working period).

II Classification

According to form of friction surface, the friction clutch used on the ships can be classified as follows:

• Disk friction clutch.

• Cone friction clutch.

• Air-actuated friction clutch.

1 Single-disk friction clutch

3- Actuating friction disk

When the axial thrust force Q is stopped, the friction disk couple

is released, and revolution of the receiving shaft will decrease and stop.

The working process of the friction clutch can be classified by three periods:

- Loading period: This is unstable working state The friction force on the friction disk surface increases from 0 to maximum and revolution of the receiving shaft also gradually increases In this period, revolution of the receiving shaft is always smaller in comparison with the actuating shaft because of relative slip of the friction disks.

- Stable working period: Revolution of the actuating shaft and the receiving shaft is the same; transmission torque is equal to friction moment of the friction clutch When operating, a little power is lost so torque on the receiving shaft is little smaller in comparison with the actuating shaft The friction clutch must be cooled to decrease temperature of the friction disk surfaces.

- Unloading period: This is also unstable working state of the friction clutch Revolution of the receiving shaft is little by little decreased and then stopped.

In fact, to reduce dimension and increase torque transmission ability, a multiple-disk friction clutch is used

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.

2 Cone friction clutch

Metal friction surface couple Metal-leather surface couple

α = 8 ÷ 10o

α = 12 ÷ 13o

a Principle

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.

3 Air-actuated friction clutch.

7

1- Actuating shaft 4- Inside drum 2- Receiving shaft 5- Inner tuber 3- Outside drum 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

6 ÷ 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

1 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::