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FEATURE // The Porsche 919 Hybrid


The technology of the title defender – maximum efficiency

The evolution of the Porsche 919 Hybrid for its third season in the FIA World Endurance Championship is based on a combination of solidly proven factors and innovations. The strong basis will remain unchaged for 2013: The structure of the chassis, as well as the hybrid drive concept with the 2 litreV4 turbocharged petrol engine and two energy recuperation systems (braking energy from the front axle and exhaust energy), will be retained. However, for 2016, the regulations stipulate a reduction in fuel consumption and fuel flow.In this way, the regulations prevent the Le Mans prototypes from becoming increasingly faster, yet at the same time fuel the engineers’ effort to generate more power from increasingly less fuel. Maximising efficiency and electrification are the decisive aspects. Porsche’s road-going sports cars also benefit from the developments on the Le Mans 919 Hybrid racer.

Right from the start, by the first 919 for the maiden 2014 season, Porsche adopted a courageous concept, with turned out to be spot on. The first 2014 spec showed exceptional potential for 2015, on wich virtually new car for 2015 was based. Now, there is less need to change and Porsche is benefiting from the stability of the concept. With every detail, the engineers asked themselves if it’s possible to make it even more robust and extract even more performance.For 2016 no changes to the concept were necessary. Porsche was able to improve every area of the car without taking big risks. This characterises the 2016 spec vehicle. Like every Porsche, the 919 Hybrid was born at the R&D Centre in Weissach near Stuttgart.

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Requirments

The regulations for the top category (Class 1 Le Mans Prototypes, or LMP1 for short) require manufacturers to use hybrid drive systems and establish a direct link between the sporty performance of the prototypes and their energy efficiency. Put simply, this means that a large amount of energy from recovery systems may be used. Hawever, this entails a proportional reduction in the permitted amount of fuel per lap, and the quantity of fuel consumed in each lap is accounted for.

WEC officials allow engineers a great degree of freedom in terms of the hybrid drive concepts that may be employed. The teams can choose between diesel and petrol engines, naturally aspirated or turbocharged engines, various displacements, and one or two energy recovery systems. This formula puts the focus on innovations that will have a huge impact on future production sportscars and this was the main reason why Porsche decided to return to the world of top level motor racing.

Combustion engine

Porsche made its debut in 2014 with the most innovative drive system on the WEC grid line up. All components were again revamped for the 2016 season. The combustion efficiency of the 2litre V4 turbocharged petrol engine, which drives the rear axle, was further increased. The LMP1 engineers in Weissach work closely with the engineers from production development. They significaly support developping the combustion engine and mixture preparation. LMP1 and production engineers also share the same dynos and test beds.

The appreciation and added value flow both ways: Technology elements from the Le Mans winning motor have been adopted in the new turbo downsizing four cylinder engines of the Porsche 718 Boxster Production car. For instance, the cylinder spacing, the short stroke design and the central direct fuel injection.

The four cylinder unit mounted in the 919, however, is not a flat unit, but V engine with 90 degree cylinder bank angle. For 2016, it shed some more weight. Last season, the outpu of the combustion engine was well above 500hp. The 2016 regulations stipulate an even lower amount of energy from fuel per lap and reduce the maximum fuel flow for all prototypes. For the 919, this means around eight per cent less fuel and power. Or in other words: ten megajoules less energy per Le Mans lap can be generated from fuel. That costs about four seconds for every 13,629Km Le Mans lap. Through the new restrictions, the performance of the combustion engine has dropped to below 500hp.

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Energy recuperation systems

With the high efficiency of the combustion engine, the recovery systems and the batteries, Porsche was the first and only manufacturer in 2015 to be able to select the highest category for electrical energy: eight megajoules per Le Mans lap.

For 2016, the components of the electric drive have become even more powerful and efficient. That applies for the optimised electric motor at the front axle, the power electronics and the new generation of lithium-ion battery cells in the in-house developed battery.

The kinetic energy produced at the front axle when braking is converted into electrical energy. The second recuperation system is installed in the exhaust tract, where the exhaust-gas stream drives a second turbine – virtually in parallel with the turbochager. It uses excess energy from the exhaust pressure that would otherwise escape into the environment. The VTG tchnology used here – that is, the variable adaptation of the turbine geometry to the level of exhaust pressure – drives the turbines, even at low engine revs and correspondingly low pressure. The additional turbine is directly connected to an electric generator. The electricity produced – along with that generated by the kinetic energy recovery system (KERS° at the front axle – is temporarily stored in lithium-ion battery cells. The driver can call up power from the cells, and if he engages the full-boost function, additional power output of more than 400hp will thrust him back into his seat. This power is applied to the front axle by the electric motor, and it temporarily transforms the 919 hybrid into an all-wheel drive race car with system power of around 900hp. For each circuit, teams and drivers work permanently on developing the strategies for when and to what extent energy is recuperated and called up per boost.

Battery

The WEC regulations allow engineers plenty of scope with regard to the energy storage medium: Initialy, the competition used flywheels and ultracaps (electrochemical supercapacitors). For 2016, they are following Porsche’s lead of lithium-ion batteries. Another important fundamental decision with the 919 hybrid was the high voltage of 800Volt – a technology that series devlopers are adopting in the Mission E concept.

In regard to the hybrid and batteyr development in particular, Oliver Blume, the CEO of Porsche AG, emphasises the pioneering role of the 919: “Thanks to our success with our electrified prototypes, we now have substantial knowledge. For instance, we don’t need to buy electric motors ready-made for our production sports cars”.

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Vehicle stucture

Like a formula 1, the Porsche 919 hybrid monocoque is a carbon-fibre sandwich construction that is manufactured as a single unit. The monocoque, combustion engine transmission as one unit ensure optimal rigidity. While the V4 engine fulfils a load-bearing function within the chassis, the hydraulicaly operated sequential 7-speed racing gearbox made of aluminium is mounted in a carbon structure. For 2016, the gearbox remain structurally identical. The focus development on thebox was on weight reduction.

Suspension, brakes and tyres

For even better driving dynamics, balance, traction, grip and set-up options, the Porsche 919 Hybrid received a new front axle and optimised rear axle for 2016. This should make the car more forgiving to drive and offer improved overall handling. The brakes also underwent improvements. Moreover, an increase in preformance on the part of th Michelin tyres is expected.

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Aerodynamics

Porsche took a three-pronged approach to aerodynamic improvments for 2016. Until now, Porsche settled on a compromise for the season-opening round of the WEC and campaigned the 919 with lower downforce than would have been ideal for the Silverstone circuit. This compromise was for the sake of the season higlight at Le Mans. The Frencj racetrack with its long straights requires very long drag, which means downfoce must be limited to what is absolutely necessary. In 2016 the 919 will start the season running a high downforce package and will be tackling Le Mans with an extremly low downforce package for the following six WEC races. The regulations prohibit more than three aerodynamic configurations per year.

The changes to the aerodynamics were driven by further improvments in efficiency and more stable handling in different driving situations. Influences such as side winds, changes in balance under cornering as well as yaw and roll angles were further reduced. The more trust drivers have, the better the lap times.

Using a 60-per cent model, Porsche tested in the wind tunnel of the Williams Formula 1 team in Grove, England. To correlate the model tests to the test results on the racetrack, Porsche’s 1:1 wind tunnel in Weissach makes an important contribution.

Another increasingly importanr high-tech tool in R&D Centre is the driving simulator. The fact that drivers can familiarise themselves with the next circuit is a welcome side effect. Set-up work takes precedence. Using simulation software, engineers develop a basic set-up for the 919, which is then refined using simulator results and driver feedback. Such a simulator is a development project in itself, almost like a second racing car. Porsche has made great progress with tool and the team is noww very well sorted with the vehicl set-up when it arrives at the racetrack.

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Headlights

While most of the improvements to the 919 hybrid are barely visible from the outside, the new headlights lend the 919 a fresh look. The four-eye optic that distinguishes it as a member of the Porsche Turbo Family was retained for the most part, but the headlights are nom equipped with significantly more LEDs. The significant increase in light energy ensures better illumination during night stints at Le Mans, Austin and Bahrain.

Start of development

The first decisions for the 2016 spec Porsche 919 hybrid were made in the spring of 2015, when a small group set th most important parameters for the suspension.

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Specifications Porsche 919 Hybrid (2016) LMP1

Monocoque:  Composite material structure consisting on carbon fibre with an aluminium honeycomb core. The monocoque was developed on the basis of the 2015 LMP regulations and was tested in accordance with the 2015 FIA crash and safety standards. The cockpit is closed.

Combustion engine: V4 engine (90 degree cylinder bank angle), turbocharged, 4 valves per cylinder, DOHC, 1 Garrett turbocharger, direct petrol injection, fully load-bearing aluminium cylinder crankcase, dry sump lubrication

Max. engine speed : 9.000/min

Engine management:  Bosch MS5

Displacement: 2.000cm3 (V4 engine)

Output:  Combustion engine : <500PS rear axle – MGU: >400PS front axle

Hybrid system:  KERS with a motor generator unit (MGU) mounted on the front axle; ERS for recuperation of energy from exhaust gases. Energy storage in a liquid-cooled lithium-ion battery (with cells from A123 systems)

Drive system:  Rear wheel drive, traction control (ASR), temporary all wheel drive at the front axle via the electric motor when boosted, hydraulically operated sequential 7 speed racing gearbox.

Chassis:  Independent front and rear wheel suspension, push-rod system with ajustable dampers.

Brake system:  Hydraulic dual-circuit brake system, monoblock light alloy brake calipers, ventilated carbon fibre brake discs (front and rear), infinitely variable control of braking force distribution by driver.

Wheels and tyres:  Forged magnesium wheel rims from BBS; Michelin radial tyres, front and rear: 310/710-18

Dimensions/weights: Minimum weight: 875kg – Length 4,650mm – Width 1,900mm – Height 1,050mm

Fuel tank capacity:  62.5 litres

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