The WR2 has been developed under the design philosophy "simple, reliable, sustainable", and is best described as the sustainable evolution of the University of Warwick’s previous year’s entry. The design focus has been on introducing sustainability into the vehicle, whilst maintaining a high standard of reliability and without compromising performance.
Team structure and operation:
The team is comprised of 11 undergraduates studying a mixture of disciplines within engineering and each team member brings a range of skills and interests to the project. Warwick Racing is organised into a matrix structure promoting cross-functional communication, and two way flow of information between the managerial team and the chassis and powertrain engineering teams. Various data management practices such as PDM have been implemented to ease communication and management of information.
Warwick Racing is based within the research centre of the Warwick Manufacturing Group, with the full support of its technical staff and researchers. Manufacturing methods and practices have been optimised in terms of quality, sustainability and time expenditure, leading to increased quality and reliability. All team members are trained on relevant machinery and adopted proper work conduct with regards to health and safety legislation throughout the whole project.
Several engine and fuel options were evaluated and the engine from a KTM 525 EXC dirt-bike was chosen. At 28kg this engine is lightweight. As a single cylinder it has a simple set up, simplifying engine mapping and easing fault diagnosis. Its compactness allows for the tight packaging in the WR2 resulting in a shorter wheelbase and weight distribution advantages. A flat torque curve provides predictable, nearly constant acceleration to the driver. As this engine was already used in previous versions of the car, a good knowledge base was provided by technicians and legacy vehicle testing data.
The final chosen plenum size offers benefits on performance without a noticeable impact on throttle response. A one piece restrictor was used in order to eliminate integrity issues identified with the previous year’s design. The plenum and runner were manufactured using carbon fibre and a bio-resin system. This process is scalable and less energy intensive than the ALM process used previously yet still allows natural shapes to be achieved. The intake system is approximately 600g lighter than the predecessor’s solution. The weight reduction is due to the throttle body selection and material choice.
Routing of the exhaust system outside the tightly packaged engine bay has allowed for improvements in many areas of the designs. The entire system has been designed to provide minimum resistance to flow, reducing power drain due to back pressure. Location of the hot exhaust away from other critical components, such as cooling and electrical components, reduced the need for heat shielding and meant that these other systems could function more reliably. Similar to the intake system, the removal and assembly of the exhaust has been simplified, something that is necessary in order to comply with the car’s modular design.
The KTM stock cooling system is designed to take advantage of the thermo-syphon effect. In the WR2, the mechanical water pump is mounted to the camshaft, inside the top-end of the engine, and so, without a sufficient head of water, it is unable to provide a good flow rate. In order to overcome coolant flow issues resulting from the lack of thermo-syphon effect, an electric pump has been introduced to assist flow, at the lowest point in the cooling circuit. The pump is controllable by the vehicle’s ECU such that the rate of cooling can be adjusted according to requirements.
The WR2 uses a crown wheel and pinion direct drive differential, which allows the engine to be mounted longitudinally so that the engine output's rotational axis is parallel to the car's centreline. This results in a very short rear end, taking full advantage of the small size of the engine, giving a lighter rear package and a shorter wheelbase.
Halfshafts and Tripods
The team chose to adapt the previous halfshaft and tripod design. Custom differential output housings accept a Tripod CV joint directly and the hubs of the car also integrate a tripod CV housing within their design. This minimises rotating mass and maximises efficiency of torque transmission. The differential placement allows the use of equal length half-shafts running at a zero degrees static angle. The half shafts are filament wound carbon fibre tubing that is bonded directly to the inner diameter of custom tripods, removing any mechanical joints via a spline. The result of this is a 3kg weight saving over conventional steel shafts.
The team opted for a change in ECU system and selected an Omex 600 as the engine controller of choice. This ECU offers fewer functions but simplifies vehicle set up.
The chassis of the WR2 takes the target, novice driver market into consideration whilst maximising handling performance.
WR2 uses a TIG welded steel spaceframe as its basis rather than an aluminium or composite monocoque configuration. The steel frame provides a strong level of torsional stiffness ensuring there is not excessive deformation under load as well as strong performance in the event of a collision whilst not adding excessive weight to the vehicle, which would negatively affect its dynamic characteristics and fuel consumption. Additionally such a structure and the associated manufacturing processes are in keeping with the costing targets of the competition when the production levels in a market environment are considered.
Finally with the target of increased sustainability being of great importance a steel spaceframe is advantageous. With energy intensive manufacturing processes such as wire electrical discharge machining disregarded in favour of manual cutting, bending and notching methods, the life-cycle environmental effects of the WR2 were reduced. Additionally Steel is highly recyclable and at a relatively low cost, thereby further reducing the impact of the car.
The dynamics of the WR2 have been designed with the end customer firmly in mind. As such, focus has been placed upon the attainment of linearity and stability of dynamic response across the entire range of vehicle operating conditions.
Wheels and Tyres
A 13" wheel size, Aluminium split wheels and Avon A45 tyres were selected.
Uprights and Hubs
The base hub design carried across from the previous vehicle has been modified to ensure sufficient adjustability of static kinematic settings. Precision machined removable brackets allow for 0°-4° of camber adjustment front/rear allowing. The placement of front tie rods allows for camber changes to be decoupled from influencing tow, simplifying vehicle set-up. Ackerman may also be adjusted from its 100% base to 80% in line with whether low/high speed cornering performance is required.
An adjustment pack aimed at the novice driver has also been designed. This allows the use of a minimum set of tools and gauges to adapt base kinematic values in line with driver preference. This also minimises the duration required to make set-up changes, allowing for the maximisation of vehicle testing time.
The springs and dampers themselves are mounted inboard to reduce unsprung mass and are actuated by pull-rods at the front and pushrods are the rear incorporating a bell-crank system. The use of a front pull-rod system has allowed for as low location in mass of the front suspension, while push-rods at the rear allow for an arrangement that reduces out of plane reaction forces at the chassis mounting points.
Front and rear ride frequencies of 3.2 and 2.9Hz respectively were selected in line with the desired roll gradient and tyre characteristics. Stiffness has been increased from the previous vehicle in line with the need to prevent the low mounted steering rack (for linearised steering motion) from grounding under vehicle dive. The wheel rates (23N/mm front & 26N/mm rear) provide an initial roll rate distribution of 48% to the front; 6% higher than that of the front static load distribution, ensuring that the rear has spare grip on corner exit to assist in applying power.
While the base roll-distribution is sufficient for meeting the vehicle dynamics targets specified, an optional rear-mounted anti-roll bar has been designed to facilitate the tuning of vehicle handling in line with driver preference.
The use of two sustainable materials has been explored with the WR2 in addition to the carbon fibre reinforced bio polymer previously mentioned for the intake system. These are unwoven flax fibre reinforced polymer for the impact attenuator and bamboo fibre reinforced bio polymer for the bodywork. When using alternative materials it is important that component performance is not compromised. This is especially the case for the safety critical impact attenuator. The offer considerable gains in other areas such as weight saving, cost, engineering innovation and, of course, life-cycle environmental impact.