Bogie and Suspension System

Bogie Overview

• A bogie is a structure underneath a railway body that carries and ties all the components of the locomotive together, and axles & wheels are attached through bearings.
• MRT Line-6's bogie is a fabricated "H-shape" frame type without end beams, composed of radius arm primary suspension, bolster-less secondary suspension with air springs and single traction link configuration.

Types of Bogie Used in MRT Line-6

• There are three types of bogies for MRT Line-6: Motor bogie, Type-1 trailer bogie, and Type-2 trailer bogie.
• Motor bogie is used only in motor cars (M1/M2/M3/M4).
• Type-1 trailer bogie is used in every Tc car's front side (cab end).
• Type-2 trailer bogie is used in every Tc car's rear bogie (near gangway).

Bogie Components

• Bogie frame: a welded fabricated "H-shape" frame type consisting of two side frames and one transom.
• Motor bogie frame has gear unit supports, motor supports, tread brake supports.
• Trailer bogie frame has disc brake supports (caliper brake supports), deflector support seats, and traction link support.
• Both bogie frames have spring seats, radius arm rubber holders, damper brackets, and air spring seats.

Primary Suspension

• The primary suspension of the bogie provides excellent ride quality and running stability.
• The primary suspension is of the radius arm type, consisting of radius arm type axle box, primary spring with rubber seat, radius arm rubber bush, primary damper (vertical damper), and wheelset hanger (axle box hanger).

Primary Suspension (Damper)

• The damper's job is to control the motion of the spring and manage the weight transfer and shock loads of the car.

Secondary Suspension

• The secondary suspension of the bogie provides excellent ride quality and running stability.
• The secondary suspension is of bolster-less suspension, consisting of centre pin installed on the carbody, two air springs, two levelling valves, one lateral damper, two lateral stop rubbers, and one single traction link with two single link rubber bushes.

Secondary Suspension (Components)

• Levelling valves: used for height adjustment between the train's floor and platform.
• Air spring: has a vertical rubber stopper to sustain the carbody safely when the two air springs in a bogie are simultaneously deflated by the differential pressure valve due to air leakage.
• Shim Plate: added under the air spring to enable adjustment of carbody height after wheel turning.

Secondary Suspension (Function)

• Two lateral stop rubbers (elastic rubber blocks) to absorb impact forces due to lateral movement.
• The centre pin with the vertical stopper installed to the carbody and the vertical stop seats installed to the bogie permit lifting of the carbody and the bogies as a complete unit.

Wheel Flange Lubricator

• The wheel flange lubrication system is of service-proven oil-mixed air injection type flange lubricator.
• Wheel flange lubricators are provided at both leading wheels of the train.
• In straight sections, the lubricator activates after every 2 minutes and sprays lubricant for 6 seconds.
• In curve sections, the lubricator activates after every 3 seconds and sprays lubricant for 6 seconds.

Bogie Maintenance

• Wheel tread profile wear limit dimensions are checked by mechanical gauge or automatic wheel profile meter.
• Wheel wear limit and diameter gauge are measured.
• Addition of shim plate is done after wheel turning operation.
• Set height for "B dimension" is provided by the formula: H = 260 + t1 + t2.

Load Transfer Mechanism

• The car + passenger load is transferred to the track in the following manner: Car load + passenger load -> secondary suspension -> bogie frame -> primary suspension -> axle box -> wheels -> track.

Tractive Force Transfer Mechanism

• The tractive force is transferred to the car body in the following manner: Traction motor -> drive gear -> axle -> axle box -> primary suspension -> bogie frame -> traction link -> centre pivot -> car body.

Braking Force Transfer Mechanism

• The braking force is transferred to the car body in the following manner: Wheel -> axle -> axle box -> primary suspension -> bogie frame -> traction link -> centre pivot -> car body.