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I am going to be talking and researching about train bogies. Train bogies are rarely noticed by the average train passenger however are the essential part of the train system and its guidance mechanism. Your average train will consist of two bogies located near the two vehicle ends. Each bogie is 4 wheeled that provides the support for the vehicle body for breaking and traction.
Contact to wheel be a 7mm radius to reduce friction.
Early in the railways upon development it was recognised that the interference from the vehicle body and the wheel needed a system to cushion and reduce the vibration felt from the train moving along the track. Suspension started in a form of leaf steel spring which was mounted on the axels of the vehicle body. The spring consists of a set of steel plates which are different lengths arranged with the longest at the top and the shortest at the base of the set and held together with a buckle in the middle.
The top steel plate of the leaf spring was secured to the underframe of the vehicle by having the ends wrapped round steel pins. The vehicle body weight was transmitted through the leaf springs to the axel box. However, with the leaf springs came problems due to the railway’s constant development and the need to go faster they had to be upgraded some of the problems with leaf springs are
Not as reliable as something with permanent housing as seen on new Alstom bogies
Springs was not set right and could move out of place it creates tensile stresses at the base of the horn that can lead to cracking under repeated loads.
Springs used today made from steel and rubber remove these defects previously seen, the new springs are in permanent housing unable to move and there is no buckle to consistently break.
Secondary suspension is provided from the lateral damper yawn damper
Anti roll bars and is used to reduce vibration on the train. A disadvantage of secondary suspension is that it is so soft, the vehicle tends to role when coming across curves. However, anti-role bars are used to countereffect this occurrence and reduce any shock there is flexibility built in the system by using rubber brushes and spherical bearings. As well as anti-roll bars being used to prevent discomfort and unstability to the bogie, the dampers are used and provides the resistive force needed to give stability to the bogie. The hydraulic damper achieves this affect from pumping oil through the small holes thus remove the generated energy from the spring system. Rubber air suspension bags are provided as the secondary suspension system for most modern trains. The air is supplied from the train’s compressed air system. The lateral damper which is located between the body and bogie is mounted at a right angle to the direction of travel thus reducing the displacement of the body going on an irregular and uneven track. Yaw dampers are fitted to high speed vehicles going to 125mph this controls the rotation of the bogie to the body when travelling.
Maintenance for primary and secondary suspension is easy to access especially as it is on the outside of the bogie so you can relatively easily spot damage and defects to the springs and dampers. Maintenance will occur on the suspension depending on the millage or type of exam which is carried out on the train, for example on a H exam you would take all the parts of the bogies off and replace/ refurbish them including the dampers and springs as it is a major overhaul. Upon completion of a bogie change/ H exam the ride height of the bogie would have to be checked which is done by applying a maximum load onto the body of the bogy and take a reading of the heights from all 4 axels and if a spring is too low or too high on one corner it is just a case of deflating/inflating the airbag.
In comparison primary suspension is more about wear to the track and maximum loads causing friction and wear to the track, compared to secondary suspension which is about comfort for the passengers and the position of the bogie moving in travel in correlation with the train.
Train wheelsets are not as simple as they seem. Train wheels have a flange on the wheel which is a safety mechanism to keep the train on the track however only if the main mechanism fails. Train wheels vary in diameter at different points of contact with the main point of contact being 7mm radius.
According to “Train wheels are conical in shape. That means they have a varying diameter at different points of contact. Now, suppose the track turns right. The train’s left wheels now must travel more than the right wheels because at the turn the track on the left is longer”.
Each brake cylinder is an air break which is provided for each wheel. The break cylinder can operate tread of disc brakes. And parking breaks as seen on the 390 pendilino. Some train bogies have two cylinders per wheel which are for heavy duty breaking. However, a pendlino has 3 break cylinders as it is operating at high speeds (125mph) so requires more force to apply to the wheel to stop the train. Each wheel has a pair of break pads which is hung from the bogie frame and activated by the links which are attached to the piston in the break cylinder. This works by applying air into the brake cylinder, the internal piston then moves the links therefore causing the brake pads to press against the discs. A break hanger support bracket carries the brake hangers that the pads are hung from.
Dampers are used to reduce the effects of the vibration that is occurring to the bogie and train movement because of the wheel and rail contact.
A steel coil spring is the primary suspension which are fitted to each axel box in Figure 3, the primary suspension spring carry’s the weight of the bogie frame and the car body. The spring compress when a load is applied to it, the springs are in a complete housing so are unlikely to fall off and break compared to the old leaf springs previously used.
Inside the axel box is the return current bush and the cover for the axel box labelled in figure 3 is protection for the brush and the axel bearing lubrication.
The bogie frame is a steel plate or made of cast steel. In figure 3 above it is a modern design of a welded steel frame where the structure is formed into hollow sections of the required shape.
The air bag suspension bags are used as a secondary suspension system for modern trains, on a pendlino bogie when a H exam is being conducted, for example most recently H5 the air bags are removed from the bolster lifted out with a crane jig and replaced with a completely new one. The air bags air is supplied from the compressed air system on the train.
On a pendilino 9 car there are 14 traction motors 2 each powered car and there are 7 cars. traction motors last depending on mileage and the wear the bearings have received. At Alstom we are conducting an exam on traction motors removed from a H exam train to prove the bearings are not as worn as they predicted to be repaired on the H6 exam to push back to the H7 exam in about 4 years, as the H6 is already a big overhaul exam. The traction motor drives the 2 axels.
Because bogies are a major component on the train, for train movement, stability and comfort, major overhauls are required of parts of the bogies depending on millage to ensure safety of the passenger and the ride of the train. This is known as the H exam and at Alstom we recently completed the H5 exam where we overhauled 1185 pendilino bogies. The H5 exam was set up on 12 road and the bogie workshop to carry out the required maintenance procedures at Manchester train care centre. The overhaul procedure was as followed:
Monday: disconnect air pipes, remove Cardon shafts and body to bogie bolts and remove the front nose cone frame of the train on 691 and 692 and the train would be lifted at the end of the day.
Tuesday: bogie move day, bogies would be moved by a shunt from 12 road into the workshop and the new bogies would be removed in reverse from the workshop into 12 road and the train would be lowered.
Wednesday: air pipes and carden shafts would be reattached and torqued to the required Nm followed by peer checks and body to bogie bolts
Thursday: plenums inside the train would be removed and hoovered and put back up
Friday: consisted of daily and safety exams and peer checks and the train would go out on the Monday.
The bogie workshop
The force on the track from the wheel cannot be too high because it would be causing more damage than necessary to the track due to the weight of the point of contact which will create an uncomfy unstable ride for passengers. To reduce this it needs to be made sure that the weight is speed evenly if it was to be spread unevenly it can cause more damage to the track if there’s more weight distributed to one wheel than the other 3 so it is necessary that all 4 wheels forces are spread evenly, as it is more likely to wear the wheels more than the track. If the wheels are worn it is only a case of shaving a part of it off on the wheel leave to make the wheelset fit for service again, compared to replacing a part of a track which would result in penalty charges. an example of this is from the Hatfield crash when a 390 pendalino de railed and upon further investigation of the crash they found the bogies of the train forces wasn’t spread evenly so the train travelling on the track multiple times of the day was actually doing more damage to the track than it was meant to be doing thus resulting in a de railement. It also within the best interest of the company supplying the train to ensure there is maximum comfort for the passengers.
Ensuring that there is less weight per bogies to car creates less damage and less disturbance to the vehicle and creates a smoother ride for the passengers as shown above in figure 7. As well as the calculations the secondary suspension needs for example the airbags need to be supplied with the air systems on the train to operate. If there was a failure to the compressor providing the air to the airbag this would cause a train to stop in traffic if it was already out on a journey which would charge penalties to the company providing the train. There is also a damper attached to the bogie at a 90 degree angle this damper provides stability to the bogie as it is moving, and the train is operating at high speeds to give that flexibility to the vehicle. Upon maintenance of a bogie inside the train depot there are various safety requirements to be followed to ensure yourself and others safety. All PPE must always be worn including:
And you must follow depot lock on procedures which are that every employee is issued with a personal padlock when going onto a road each padlock is coloured and for specific safety requirements.
In conclusion there are numerous types of suspension found on different types of bogies. Development of the railway and the need for trains to go faster results in the development of bogies and different types of springs being used and suspension to find that perfect fit for the train. There are always adjustments being made from leaf springs, to rubber a steel springs to provide better housing and stability. There is also the need to inspect the bogie regularly when it encounters the millage required for inspection to ensure the bogie is delivering the maximum performance and the weight is being distributed evenly across all 4 axels.
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