Laser-Sintered Titanium Parts Boost Race Car's Performance

A novel, active suspension system helped Coventry University’s Phoenix Racing team to win the Shell-sponsored award for most fuel-efficient car in the premier class of this year's Formula Student championship. Key components of the system, which were both compact and lightweight, were produced layer-by-layer from titanium alloy powder (Ti64) in EOS laser-sintering machines.

At Silverstone in July 2011, against fierce competition from over 100 universities around the world, the single-seater racing car was placed 20th overall. It was 5th in the endurance challenge, involving a separate, 22 km race during which the cars prove their speed and durability and the students execute a pit-stop and driver change.

Comprising third-year motorsport engineering students at Coventry University, Phoenix Racing, under team leader, Dan Priestman, this year produced its most advanced and successful car in over 10 years of racing in the Formula Student competition. The students took full advantage of the university’s motorsport workshop, in particular the direct metal laser-sintering (DMLS) machines which were made available through sponsorship by laser-sintering equipment manufacturer, EOS.

The equipment allowed the students to manufacture intricate titanium parts for an electronically-controlled, hydraulic anti-roll system to ensure that the car maintained grip in the corners, a clever design feature that was acknowledged by the judges. All were industry professionals that had not previously come across such a system at the competition.

Causing a stir

Considerable interest was also shown in the active front suspension by a number of firms in the motorsport and automotive sectors, including Mercedes-Benz Grand Prix, Mercedes-Benz HighPerformanceEngines and Jaguar Land Rover.

Other Formula Student competitors were similarly curious, so much so that the team had to keep the system covered while the race car was being worked on to allow enough space around the vehicle.

Towards the end of the event, rumours had travelled up and down the pit lane suggesting that a top international team had spent the previous two nights trying to reverse-engineer the system, which was comically nicknamed the Doomsday Device at the championship.

Development of the hydraulic anti-roll system

The Phoenix race car was designed by the students under the guidance of Charles Kingdom, Senior Lecturer Materials and Engineering Design at Coventry University. Early on in the project, it became clear that the position of the front roll centre was below ground level, which increased the lateral transfer load, created a large body roll angle and produced a pronounced understeer.

This implied that a front anti-roll bar might be required.  However, a traditional bar could not be used, first because technical regulations meant that the feature would be outside the allowed chassis envelope, and secondly because it would have been difficult to fix the suspension pick-up due to the location of the front rockers. A further drawback with a passive anti-roll bar is that it transmits a single wheel bump around the whole chassis.

Phoenix Racing's new, active anti-roll system, which was the brainchild of student team member, Tom Edwardes, consists of two double-acting hydraulic cylinders connected top to bottom from left to right.  The actuators are fixed at one end to the front suspension rockers and at the other end to the vehicle chassis.  As one actuator compresses, the opposite actuator also compresses. In this simplistic form, the system mimics an infinitely stiff roll bar, so a method of varying the difference between the two actuators was required to allow roll resistance to be adjustable.

Two valve blocks were therefore added in-line, each consisting of a piston and a spring.  As the right-hand cylinder compresses during cornering, the fluid is displaced into the right-hand valve block. The piston compresses the spring, resulting in less fluid moving into the left hand cylinder.  This results in a difference in displacement between the two actuators.  The left hand valve block moves downwards to equalise the difference in fluid that is displaced.

Additive manufacture creates compact components

The actuator casing was manufactured from Ti64 powder using the DMLS process from EOS.  The additive procedure allows complex structures to be manufactured, directly from a CAD model, that would often be difficult or impossible to machine conventionally, such as the spiral oil feed pipe around the cylinder body. DMLS also frequently results in the component being smaller and lighter than it would otherwise be using traditional manufacturing techniques, in this case reducing the weight of the race car and making the components easier to install.

EOS produced the actuator casing and the rod end in collaboration with the University of Wolverhampton, while the internals were manufactured at Coventry University. Machining of the titanium parts was carried out at James Camden Engineering, Warwick, and at the University of Wolverhampton, where Dr Mark Stanford worked for many hours to make some of the finished items.  The cylinder bores were honed at Crosshatch Services, Coventry, and the hydraulic fittings were supplied by Brown & Miller Racing Solutions, Slough.  Overall length of the unit is 170 mm, with a bore of 25 mm and a 22 mm stroke. Weight is just 300 grams.

The valve blocks were also manufactured from Ti64 using DMLS.  It allowed the overall length of the units to be reduced by locating two hydraulic fittings alongside each valve body rather than at one end, both fittings being fed via two flow pipes running from the bottom of the block.  The component also features a mounting face and feet to locate the valve block to the chassis tubes.

Within the block are a piston, spring holder, spring and compressor.  The latter can be used to preload the spring within the holder using a one-millimetre pitch thread machined into the top half of the titanium casing. This allows the roll resistance of the vehicle to be adjusted either by the preload or by changing the spring.  The unit has a bore of 30 mm, an overall length of 120 mm and a mass of 450 grams.

Features and benefits of the hydraulic active system compared with a traditional anti-roll bar may be summarised as follows:

•    The active suspension is easily packaged within the chassis.
•    Roll stiffness can be quickly and simply adjusted, even by the driver.
•    The roll mechanism is damped.
•    Weight is comparable to that of a standard anti-roll system.
•    The energy of a single wheel bump is absorbed.
•    It is possible to develop the technique further into a full vehicle system to incorporate pitch and dive resistance.

EOS was founded in 1989 and is today the world's leading manufacturer of laser-sintering systems. Laser-sintering is the key technology for e-Manufacturing, the fast, flexible and cost effective production of products, patterns and tools. The technology manufactures parts for every phase of the product life cycle, directly from electronic data. Laser-sintering accelerates product development and optimises production processes. EOS completed its business year 2010/2011 with revenues of more than 90 million Euros (124.3 million US$). The company employs 300 people worldwide, 250 of them in Krailling near Munich, Germany.

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