Crash!

Figure 1: The hydraulic buffer braking system

Department of Mechanical, Materials & Manufacturing Engineering

MM4GDM Group Design & Make Project

Hydraulic cylinder

Buffer head

Reservoir bag

Force translation rods

Orifice plate & reservoir connector

Front & back supports

Block connector

Front mount & locks

Emergency stop buffers & square beamsHinge mechanism

This project involved the design and make of a mechanism to stop a 100kg sled of a crash track at accelerations of up to 100g. The customer has an existing stopping mechanism but is limited by the cost of manufacture of disposable components and the long amount of time taken (up to 3 hours) to reset the sled. The mechanism must allow the shape of the acceleration pulse to be programmed – the minimum requirements are to deliver constant and ramped acceleration pulses. Likewise running costs should be minimal or zero and the reset time should be very short.

Aim

ConceptThe hydraulic buffer system consists of a plunger with a metering pin fixed to the end, housed inside a cylinder submerged with hydraulic fluid. When the sled impacts the buffer’s head, the plunger is displaced, forcing hydraulic fluid through an orifice and dissipating the kinetic energy of the sled into thermal energy in the oil. The metering pin regulates the flow of oil through the orifice and the resultant force exerted on the sled by the buffer can be controlled by modifying the size of the gap between the orifice and the plunger’s metering pin. This was done by changing the profile of the metering pin’s cross-sectional area. Different sections of the metering pin are different sizes depending on the mass and speed of the sled that is being tested.

Design

Programming

Figure 2: Extract from the SIMULINK model

Results of Prototype Testing

The formula derived for the relationship between the size of the metering pin and the resultant force against the motion of the sled was modelled using MATLAB and SIMULINK. This enabled plots of acceleration pulse graphs to be created over the duration of impact as a function of the metering pin profile.•A MATLAB function allowed arbitrary values of the metering pin radius to be entered for different displacements of the piston head, x, during impact.•Each variable comprising the resultant force equation was converted into SIMULINK and this was linked directly to the MATLAB function.•Values of the metering pin radius were changed for different sled masses to see how this affected the force, acceleration, velocity, displacement. By iteration, constant and ramped force/acceleration profiles were found.•A table of metering pin profiles was collated.

Figure 3: Table of metering pin profiles