Load holding

An E-shaped suspension system designed at Cambridge University promises to provide drivers of heavy trucks, buses, coaches and commercial vehicles with a comfortable ride — no matter what size load they are carrying.

The E-Spring is scalable, so can be used in vehicles ranging from SUVs and light pick-ups to heavy trucks and HGVs. This means that it could potentially be used in miniature mechanical systems such as actuators, gears and valves.

Currently, commercial vehicles and HGVs must have their suspensions fine-tuned for the load they are carrying to provide drivers with the best possible vehicle handling and control.

However, a vehicle whose suspension has been tuned to be soft in anticipation of carrying light loads becomes difficult to control if it has to carry extra weight.

And while tuning a vehicle such as an HGV to have a hard suspension can make heavy loads easy to handle, once that weight is removed, driver and passenger comfort diminishes and handling also suffers.

To solve this problem, instead of the single spring used in standard suspensions, Cambridge’s suspension system uses two. These are placed opposite to one another, but can work together when needed. The first operates under light loads, compressing under force, while the second is more tightly set, so that it provides greater stiffness only when the weight of the vehicle’s load is heavier.

As a result, the vehicle’s suspension adjusts itself, according to the vehicle’s needs, without needing extra tuning. driver control is therefore enhanced, while comfort is improved and safety increased.

The E-Spring is also claimed to be 25 per cent lighter and takes up less space than traditional suspension systems, meaning it also has the potential to reduce overall vehicle weight and use less fuel. It will also remove the cost of fitting specialist equipment to vehicles so that they can cope with different loads.

‘With load-carrying vehicles there are three conflicting requirements — ride comfort, road holding and load carrying capacity,’ said designer Salah Elmonselhy, of Cambridge’s department of engineering. ‘It took six months to end up with the shape, which was then analysed then optimised.’

He said the technology has even more advantages over traditional systems as he has manufactured the device from a material he calls a hybrid micro-composite structure. In this, woven E-glass fibres are impregnated into either a metallic matrix such as nickel super alloy or a polymeric matrix such as iso-phthalic polyester that is reinforced at the micro-scale by either E-glass powder fibre or clay powder. This, he said, makes the material exceptionally strong compared to, say, alloy steel.

‘For the same maximum induced stress level, the E-spring can have deflection capacity of 25 per cent more than that of a semi-elliptic multi-leaf spring and three times that of a C-spring,’ he said.

‘In addition, when it comes to vertical stress deflection, the spring can have double the maximum load carrying capacity of a helical spring.’

To cope with lateral forces such as when cornering, as well as longitudinal forces such as driving-off and braking, Elmonselhy said that a simple C-channel sliding mechanism could be attached to the E-spring to make the device completely resistant to these horizontal forces. ‘It is also lightweight and low cost, making it a very cost effective attachment,’ he explained.

The E-spring requires 75 per cent less of rattle space in comparison with traditional semi-elliptic multi-leaf springs. ‘It is a very strong structure and is extremely tough, particularly given its weight,’ said Elmonselhy. ‘In addition, it has improved vibration control and life over steel. In all, there are 10 advantages of the E-Spring over the types of suspension that are currently in use.’

Elmonselhy is now looking for manufacturers for the device, which he says has already attracted some positive feedback from major OEMs, such as General Motors.

Julia Pierce