UNIT 3 –
UNIT – III. Syllabus
Types: mini bus, single and double decker, decker, two level, split spli t level and articulated bus. Bus body layout floor height, engine location, entrance and exit location, seating dimensions. –
Constructional details: Frame construction, Double skin construction.
Types of metal section used, Regulation.
Conventional and integral type construction.
Buses are used for the transportation of people. people .
CLASSIFICATION OF BUSES: 1) Based on distance distance travelled. travelled. 2) Based on capacity of passengers. 3) Based on style. 1) BASED ON DISTANCE TRAVELLED: TRAVELLED: a) Town buses. b) Suburban buses. c) Intercity coaches. d) Touring coaches.
2) BASED BASED ON CAP CA PACITY OF PASSENGE PASSENGERS: RS: a) Mini bus 8 to 15 (Nos of seats) 16 to 30 b) Small coaches for long distance c) Small buses for town upto 40 d) Medium coach for long distance 31 to 45 e) Medium buses for town 41 to 60 46 to 60 f) Large coaches for long distance g) Large Large buses buses for town 61 to 80 h) V Very ery large large buses for town town > 80
3) BASED ON STYLE: a) Normal control type b) Single decker c) Double decker d) Two level e) Split level f) Articulated bus
NORMAL CONTROL BUS: This type of bus has the engine in front of the passenger carrying compartment. This design which has almost universal at one time has practically disappear and is mainly of historical interest.
In this type the driver compartment is behind the engine. This has less space because the front part is stretched out. This also has poor aero dynamical design which decrease the fuel economy. So this type of buses are not in use now a days. The angle of vision is low because of longer front part.
SINGLE DECKER: The single deck bus is almost universal today as this layout eliminates all the disadvantages of above type. single-decker is a bus that has a single level. Normally the use of the term single-decker refers to a standard 2 axled rigid bus.
These type have the engine mounted in or below the drivers cab. It has an advantage of more length for more seating capacity. These have two doors for shorter distance travel and have only one door for longer distance of travel. These type of vehicle have a maximum of 52 seats and a minimum of 30. It has a better angle of vision than normal control type. It has roof rack for hand luggage.
DOUBLE DECKER: These vehicles have more number of seats for a given overall length. Stability is not so high compared to single ducker. It has an extra deck and staircase. It has one or more doors and varying engine positions.
Double deck buses are used to reduce the traffic by having an seating capacity of 65 75 passengers. These are used in metropolitan cities. It has rear engine to reduce noise and to have higher track co-efficient. –
SPLIT LEVEL:
It is intermediate solution between single and double ducker. It having more seats than single ducker and more stability than Double Ducker. It has not been widely accepted.
TWO LEVEL: It is used for luxury coaches. This layout provides good forward visibility for all passengers. good luggage space and easy installation of an under floor or rear engine.
Additional windows are provided to improve visibility of the passengers. The driver compartment is separated from the passengers compartment. This type is only made for special orders as it is not easy to make derivations from the same body shell.
ARTICULATED BUS: Bodies for very large coaches or in particular city buses are often made in two parts because of axial load limitations. Articulated buses are buses of a type with an increased passenger capacity. Found almost exclusively in public transportation use. These buses are approximately 18 m (60 ft) long, while regular buses are 11 to 14 m (35-45 ft) long. This type of bus is also known as accordion bus, harmonica bus, jointed bus, or bendy bus, all because of the shape of the bellow and the fact that the design of the turntable joint allows for sharp turns. To make them nimble enough to safely navigate streets at their increased length, they are fitted with an extra axle (set of wheels).
A joint usually located slightly behind the midpoint of the bus, behind the second axle. Some models of articulated buses have a steering arrangement on the rearmost axle which turns slightly in opposition to the front steering axle, which allows the vehicle to negotiate turns in a somewhat crab-like fashion, an arrangement similar to that used on long hook-and-ladder fire trucks operating in city environments
MINI BUS: It should have a seating capacity upto 25. It built on light duty truck chassis. It has front mounted engine and rear axle drive. It has soft and comfort suspension. It has reasonably comfortable seat. It has fairly small entry platforms.
TOWN BUS or CITY BUS: It is for short distance journeys of about 30 km. It has large standing space. It has relatively hard seating, covered with durable trim materials such as PVC etc. Due to short intervals between stops in local traffic, wide entrance and exit are provided with low steps entry and exit platforms.
SUB-URBAN BUS: It is used for a distance of journeys of about 40 kms. Thus they have reasonably comfortable seats. It has roof rack for luggage. It has a small entry platform with single door. The seating capacity is 38+3.
INTERCITY COACH: It is used for a distance of about 40 km. It has reasonably comfortable seats. Small entry platform. Thus the extra space can be utilized for extra standing or for luggage. Just a door is sufficient.
TOURING COACH: Very comfortable pushback seats. There is a additional window to improve visibility for passenger. Roof rack for luggage. There may be a/c, television, dvd, and music facilities.
FLOOR HEIGHT:
The floor should be placed as low as possible so that distance of centre of gravity of bus from road surface is small. The stability of the bus gets increased. It gives easy entry to the bus. It is easy to place luggage in bus. Due to the lower height, the Bus design is more complicated in separate chassis and body construction.
Considering floor level, the chassis frame are made specially shaped. If an integral body is used, low floor level becomes much easier to design. Large number of passengers can be seated in the bus.
ENGINE LOCATION: According to location of engine, there are five types as given in figure. a) Engine behind front axle. b) Engine above front axle. c) Engine in front of front axle. d) Engine at rear. e) Under floor engine.
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Advantages of different engine locations are To improve visibility (i.e.) forward and side visibility. Reducing extra placing space of engine. It improves space for passenger in bus.
ENTRANCE AND EXIT LOCATION: Generally in all types of buses, back side door is for entrance. Front side door (nearer to driver) is exit. In city bus, back and front door are as usual. But middle door is for easy exit for more number of passengers at a time. In city bus, the door width is more. In sub urban bus, the entrance is at the middle and exit is at the front. In long distance bus, the back door is for entrance and front door is for exit. In long distance bus, the door size (i.e.) width of the door is less.
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SEATING DIMENSIONS:
If the seat is comfortable, the journey may be a pleasure trip But it will be a trouble some, tiring, agony, if the seat is uncomfortable. The design of seat is designed to the structure of man. Passenger seat is designed for comfort and also described according to distance between the consecutive seats.
Seats are manufactured by the materials a) Natural rubber latex b) Cold
cure polyester (or) urethane c) Hot cure foams (or) chip forms. –
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In passenger seat, the seating angle ranges from 5 0 and 100 In push back seating, the seating angle is included to 60 0
BUS BODY LAYOUT:
Cant rail
Waist rail Side rail Crib rail Skirt rail
Roof longitudinal Roof panels
Rear dome panel
Roof stick
Cross bearers
Cant rail Waist rail
Front canopy panel
Truss panels
Main side rail
Wind screen aperture
Side piller Skirt rail
Front grille panel Wheel arch
Entrance door aperture
N/S Bay 4 Piller cappings
Bay 3 Bay 2 Bay 1
Valance panel Skirt panel Main side panel O/S Roof panel
Access flap
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According to Chassis design the body can divided into 1. Conventional Type construction 2. Integral Type construction 3. Semi- Integral Type construction
CONVENTIONAL TYPE CONSTRUCTION: (It also called as “Separate body and chassis type”, “Orthodox type”)
The body and chassis will be as separate unit. Bolts are used to join the body and chassis together. The separate part of body will be placed over the top of the chassis. A rubber block will be placed in between these two parts to avoid the vibration. The conventional type building involves in building up of a ladder type frame with two long side members interconnected by cross members at intervals. The units like engine, gear box, radiator, axles, steering wheel, fuel tank are mounted on the frame.
The whole body and passenger load is transmitted to the chassis by means of spring. Chassis should be built strong so that it can withstand the weight of the body. The frame sections are used generally,
a. Channel Section - Good resistance to bending b. Tabular Section - Good resistance to Torsion c. Box Section - Good resistance to both bending and Torsion
The basic under body structure is fabricated only thin mild steel cold rolled channel sections It is fully galvanized for corrosion protection. It is provided with cross members and out riggers at specified intervals. The pillar and roof shocks are made of sheet steel. Pillars are bolted to the sole bar of the under structure.
The roof sticks are connected to the pillars by stiff pressed steel corner brackets and joined by solid rivets. All the inner panels and wheel arch truss panels are sheet steel and solid steel riveted to the pillars. All the outer panels and roof panels are pop riveted.
Advantage: 1. This is used in heavy vehicle. 2. This is of simple construction. 3. The change of designing and the alteration of frame length is easy. 4. Servicing is easy in case of any damage. 5. There is no need for more expenditure for preventing corrosion.
Disadvantage: The weight of the frame is more, due to this the vehicle speed is 1. decreased. More fuel is also required. 2. Since the floor height is more, the centre of gravity from the ground will also be more. Due to this, the stability will be decreased. INTEGRAL TYPE CONSTRUCTION (Also called as integral monocoque construction) There is no separate chassis and body. It contains only body structure and under structure. Only the under frame is used for mounting the engine, gearbox, and the running unit. In this under frame, there is no need for carrying the complete passenger load. The complete unit (roof, floor, body side) shares the load. Due to this roof, body side, f loor are made strong and stiff.
Construction:
A box structure is formed by building a structure with four long side members, cross members, out riggers and wheel arch supports. The units like engine, gearbox, axle etc. are mounted on the flexible under structure which is fabricated by welding. The under structure is painted with suitable and specified paints for better protection against corrosion. The body pillars attached to the extreme side member called role bars by bolting. The paneling is done as per the specification to give a good internal structure. The under structure and body structure will acts as a single structure to carry the load.
Design: Chassis under structure: The weights like engine, gearbox, radiator, steering box, batteries and fuel tank acting on point load at mounting points. The weight of under structure should be considered as uniformly distributed load.
Chassis body structure: The loads to be considered for body structure as, Body weight is considered as uniformly distributed load. The pay load is also considered as uniformly distributed load.
Advantage: 1. 2. 3. 4. 5. 6. 7. 8. 9.
Light in weight compared with conventional type of body construction. so fuel consumption is less. Easy entry/ exit and lower floor height is to be achieved. Greater strength. Free from squeaks and rattles caused by the working of bolted joints which are absent in this construction. Reduction in heat in the driver and passenger area. Low noise and vibration level. Lowered wind screen level and better visibility for driver. Assembling of component is easy. Mainly this type is used in car construction.
Disadvantages: 1. 2. 3. 4. 5. 6.
when a car is involved in an accident, it is more expensive to repair the large panel sections. There is a greater liability of injury to the driver. It is more expensive to introduce changes in body styling to keep abreast of the times. Initial cost is more. Thick gauge material should be used. More money is required to avoid corrosion.
CONSTRUCTIONAL DETAILS 1. Frame construction 2. Double skin construction FRAME CONSTRUCTIONAL DETAILS: The design of bus body is based on the use of a light metal frame, brased by stressed metal panels. The main framing is of light members of thin gauge material formed by folding, pressing, stretch forming, rolling, extrusion and connected by gussets generally riveted to the structure framework which is applied to the inside face of the framing.
Sequence of bus building operation: 1) Chassis preparation: The floor frame is placed in position. Holding down bolts fixed. All the parts of the chassis painted.
2) Side and front framing: The body side framing and front end is assembled. Truss panels bolted into position. The body lined up with the waist rail. The lower bolts tightened.
3)Roof and end framing: The roof and end framing are designed with respect to the aerodynamic shape of the vehicle.
The roof and body ends framing are positioned and fixed. The frames are painted finally for good appearance.
4) Door step installation:
The wheel boxes and entrance steps installed. In town buses, steps are placed wide at the rear. In luxury buses, steps are placed in the front. In mountain vehicles, steps are placed in the rear. The design of steps should not affect the opening and closing of the doors.
5) Riveting:
Truss panels between the waist rail and seat rail over the wheel- arches are riveted into position.
6) General inspection: General inspection of finished framing to ensure All structural bolts are tight. Truss panels securely riveted.
7) Floor riveting: Floor and interior lining panels fixed. Riveted into position.
8) Roof panels riveting: Roof panels are fixed and riveted.
9) Door and window installing:
Side windows are riveted. Windscreens fixed inside ceiling panels. The door hinge and pillars are positioned. The beading is done.
10) Interior work: Interior works are done with sealing plywood, fabric, PVC etc to increase the beauty of the vehicle. Mouldings, pillar cappings and electric light fittings fixed.
11) Seats: Tubular seat frames are positioned and bolted through the f loor and seat rail. Extra floor covering and treads fixed, stanchions and grab handles are fitted.
12) Final finishing and inspection: Final finishing and inspection is made after all the body works. All the inspection like area of rivets, bolt, tightness of nuts, electrical works, seating arrangement is done. Then the vehicle is made to run in rough roads and the drawbacks are rectified. After these tests, leak test has to be conducted. Finally painting is done to give good appearance.
DOUBLE SKIN CONSTRUCTIONAL DETAILS: Normally inner skin will take part in load carrying Outer skin will be fixed in such a way that it can be replaced easily. (a)Interior paneling:
this is the paneling done in side the vehicle. The paneling inside the body gives comfort to the passengers. The factors to be considered during paneling are safety, easy maintenance, easy cleaning. Decorated laminated sheet are used for this. When laminated sheet and aluminium and stainless steel are combined give the good look. GRPF (glass reinforced plastic fiber) can also be used for this purpose. Floor side panel and roof has to be thermal insulated or sprayed.
(b) Exterior paneling:
The paneling done on the exterior is called as exterior paneling. This is also called as skin of the vehicle. This does not take any load. This is done by galvanized steel sheet coated with zinc coating. The galvanized steel sheet is welded or riveted to form panel. The body paneling is done by two ways.
Small panels are attached together according to the requirement. To make a single big panel for the whole length.
Steel sheets are used in the uneven surface. This increase the beauty. To avoid corrosion, leak and vibration, the panel should be made with plastic trim fillet. The normally used material for exterior paneling is aluminium.
TYPES OF METAL SECTION USED: a. Channel Section
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- Good resistance to bending
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b. Tabular Section - Good resistance to Torsion
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c. Box Section - Good resistance to both bending and Torsion
