By May 27, 2013 Read More →

Porsche 918 Spyder’s hybrid drivetrain

Porsche 918 Spyder_05The Porsche 918 Spyder’s hybrid drivetrain combines maximum performance with minimum consumption. Drivers can experience no-compromise driving dynamics thanks to the unique all-wheel drive concept with a combination of combustion engine and electric motor on the rear axle and the second electric motor on the front axle.

V8 engine

The main source of propulsion is the 4.6-litre, eight cylinder engine that produces 608 hp of power. The engine is derived directly from the power unit of the successful RS Spyder, which explains why it can deliver engine speeds of up to 9,150 rpm. It features dry-sump lubrication with a separate oil tank and oil extraction. To save weight, components such as the oil tank, the air filter box integrated into the subframe and the air induction are made of carbon fibre reinforced polymer. Further extensive lightweight design measures have resulted in such features as titanium connecting rods, thin-wall, low-pressure casting on the crank case and the cylinder heads, a high-strength, lightweight steel crankshaft with 180 degrees crankpin offset and the extremely thin-walled alloy steel/nickel exhaust system. Striking features of the V8 are that it no longer supports any auxiliary systems, there are no external belt drives and the engine is therefore particularly compact. Weight and performance optimisations achieve a power output per litre of approx. 132 hp/l – the highest power output per litre of a Porsche naturally aspirated engine – which is significantly higher than that of the Carrera GT (106 hp/l).

Electric motor

The hybrid module comprises a 115 kW electric motor and a decoupler that serves as the connection with the combustion engine. Because of its parallel hybrid configuration, the 918 Spyder can be powered at the rear axle either individually by the combustion engine or electric motor or via both drives jointly. As is typical for a Porsche super sports car, the power pack in the 918 Spyder has been placed in front of the rear axle, and does not have any direct mechanical connection to the front axle.

On the front axle, there is another independent electric motor with an output of approximately 95 kW. The front electric drive unit drives the wheels at a fixed ratio. A decoupler decouples the electric motor at high speeds to prevent the motor from over-revving. Drive torque is independently controlled for each axle. This makes for very responsive all-wheel drive functionality that offers great potential in terms of traction and driving dynamics.

The core of the 918 Spyder concept is its distribution of propulsive power among the three power units. Their cooperation is controlled by an intelligent management system. To best exploit these different approaches, the Porsche developers defined five operating modes that can be activated via a switch on the steering wheel.

E-Power

When the vehicle is started up, the “E-Power” mode is the default operating mode as long as the battery is sufficiently charged. In ideal conditions, the 918 Spyder can cover over 30 kilometres on purely electric power. Even in pure electric mode, the 918 Spyder accelerates from 0 to 100 km/h in less than seven seconds and can reach speeds of up to 150 km/h. In this mode, the combustion engine is only used when needed. If the battery’s charge state drops below a set minimum value, the vehicle automatically switches to hybrid mode.

Hybrid

In “Hybrid” mode, the electric motors and combustion engine work alternately with a focus on maximum efficiency and minimum fuel consumption. The use of individual drive components is modified as a function of the current driving situation and the desired performance. The Hybrid mode is typically used for a fuel economy-oriented driving style.

Sport Hybrid

In more dynamic situations, the 918 Spyder selects the “Sport Hybrid” mode for its power sources. The combustion engine now operates continuously and provides the main propulsive force. In addition, the electric motors provide support in the form of electric boosting or when the operating point of the combustion engine can be optimised for greater efficiency. The focus of this mode is on performance and a sporty driving style at top speed.

Race Hybrid

“Race Hybrid” is the mode for maximum performance and an especially sporty driving style. The combustion engine is chiefly used under high load, and charges the battery when the driver is not utilising its maximum output. Again, the electric motors provide additional support in the form of boosting. Furthermore, the gear-shifting programme of the PDK is set up for even sportier driving. The electric motors are used up to the maximum power output limit to deliver the best possible performance for the race track. In this mode, the battery charge state is not kept constant, rather it fluctuates over the entire charge range. In contrast to Sport Hybrid mode, the electric motors run at their maximum power output limit for a short time for better boosting. This increased output is balanced by the combustion engine charging the battery more intensively. Electric power is thus available even with several very fast laps.

Hot Lap

The “Hot Lap” button in the middle of the map switch releases the final reserves of the 918 Spyder and can only be activated in “Race Hybrid” mode. Similar to a qualification mode, this pushes the traction battery to its maximum power output limits for a few fast laps. This mode uses all of the available energy in the battery.

PDK transmission

A seven-speed Doppelkupplung (PDK) transmission handles power transmission to the rear axle. The high-performance transmission is the sportiest version of the successful PDK; it has undergone a complete redesign for the 918 Spyder and has been further optimised for high performance. To ensure a low mounting position for a low centre of gravity of the entire vehicle, the gear unit was turned “upside down” by rotating it 180 degrees about its longitudinal axis, in contrast to other Porsche series. If no power is required on the rear axle, the two motors can be decoupled by opening the decoupler and PDK clutches. This is the action behind the Porsche hybrid drive’s typical “coasting” with the combustion engine switched off.

Lithium-ion battery

The electric energy for the electric motors is stored by a liquid-cooled lithium-ion battery comprising 312 individual cells with an energy content of about seven kilowatt hours. The battery of the 918 Spyder has a performance-oriented design in terms of both power charging and output, so that it can fulfil the performance requirements of the electric motor. The power capacity and the operating life of the lithium-ion traction battery depend on several factors, including thermal conditions. That is why the battery of the 918 Spyder is liquid-cooled by a dedicated cooling circuit. The global warranty period for the traction battery is seven years.

Recharging

To supply it with energy, Porsche developed a new system with a plug-in vehicle charge port and improved recuperation potential. This vehicle charge port in the B-column on the front passenger side lets users connect the storage battery to a mains supply at home and charge it. The charge port is standardised for the country of purchase. The on-board charger is located close to the traction battery. It converts the alternating current of the mains supply into direct current with a maximum charge output of 3.6 kW. Using the supplied Porsche Universal Charger (AC), the traction battery can be charged within four hours from a ten ampere rated, fused power socket on the German 230 Volt mains supply, for example. Furthermore, the Porsche Universal Charger (AC) can be installed at home in the garage using the Charging Dock. It enables rapid and convenient charging within approximately two hours, irrespective of regional conditions. The Porsche Speed Charging Station (DC) is available as an optional extra. It can fully charge the high-voltage battery of the 918 Spyder in just 25 minutes.

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