ALS (Active Lateral Suspension) By Bernard GAUTIER SNCF

Transcription

1 ALS (Active Lateral Suspension) By Bernard GAUTIER SNCF The vertical and lateral motions of a railway vehicle come from the track and the wheel - rail contact dynamics. The motions of the vehicle determinate the comfort felt by the travellers. It is well known that when the speed increases, the motions of the vehicle also increase and the comfort decreases. Often in a train, comfort decreases from the front to the back (snaking phenomenon). The customers of the Railway Company want to be transported more and more comfortably and quickly. Let's have a look on the TGV (French High Speed Train): In 1981, the TGV commercial speed was 260 km/h. In 1983, the speed becomes 270 km/h In 1989, with the opening of the high-speed line n 2, the TGV commercial speed has reached 300 km/h. And in few years, 320 km/h. To come up to our customer's expectations, special high-speed lines have been made (Japan, Italy, France, Spain, ), but as the speed of the trains increases, it is not enough. A step has been made with the air spring suspension essentially but conventional passive suspension technologies achieve their limits essentially in lateral direction. When the bogie has a displacement of x, the force transmit to the car body is F = K. x and the acceleration is = F / M = K. x / M. To reduce the motion of the car body, the stiffness of the suspension must be as small as possible.

2 When the car body has an acceleration, for example in curve, the displacement between the car body and the bogie is x = M. / K. If the suspension is too soft, the risk of contact with stop lugs increases. In 1994, with Alstom and TRW aeronautical systems, a research programme was launched by SNCF to design and implement an active system with the following objectives: On high-speed line, the comfort at 360 km/h with the active system must be equal to or better than the comfort at 300 km/h without it. On classic line (speed under 220 km/h but higher cant deficiency), at the same speed, the comfort with the active system must be equal to or better than the comfort without it. The snaking phenomenon must be reduced. The project stages are: Drawing up specifications Carrying out theoretical studies using simulations and predetermining the parameters using VOCODYM software. Building prototypes to equip a TGV half-trainset (four bogies) to validate the concept. Optimising command-control system parameters Extending to full trainset. To obtain the objectives, the following principles have been chosen: Softening the secondary lateral suspension for a better comfort in straight line. Recentring the car body in relation to the bogie to increase comfort in curve Introducing a lateral damping to reduce the snaking phenomenon Using the structure of the trainset to anticipate the actions.

3 An accelerometer on the first bogie of the trainset measures the lateral accelerations. A computer in the front car calculates the cant deficiency and transmits the value to the computer of the other bogies. Each bogie has an electric actuator witch is able to measure the displacement between the bogie and the car body. The actuator applies a force calculated by a local computer. The force is the result of different elements: Recentring action: the force is determined from the cant deficiency and the mass of the car body. The principle is the same as a tilting action. Softening of the secondary suspension action: the force is determined from the displacement between the bogie and the car body. Damping action: the force is determined from the displacement between the bogie and the car body.

4 Due to safety measure when the system breaks down, for example slow speed in rail switching, the stiffness of the secondary springs is classic. To soften the suspension, the actuator has to apply a force in the direction of the displacement. The Active Lateral Suspension concept has been validated on the TGV n 511. The equipment of the trainset was: Four bogies fitted with actuator and local computer in the car body Each motor coach is fitted with a computer and a front sensor (accelerometer) Accelerometers in all car bodies to quantify the comfort. Many test runs have been done at different speeds (300, 330, 350 km/h) without the actuator (reference), with the actuator fitted out but non active, with operational Active Lateral Suspension. Those tests have shown that: The functional part of the Active Lateral Suspension is validated (collect of the input data, computation of the data, sending of the parameters, transition active-passive mode and passive-active mode, ) The objectives of comfort at very high speed are reached The recentring in curve operate correctly in a space of 20 mm. The snacking phenomenon is strongly attenuated

5 As often, making improvements gives some disadvantages: mounting an actuator between the bogie and the car body introduces a connection and more vibrations arrive at the car body. Nevertheless the level of those vibrations stays enough low to not disturb the traveller's comfort. Considering the results of those tests, the SNCF doesn't rule out the possibility to use this technology for a new TGV able to a commercial speed higher than 300 km/h.