Porsche broke a “golden rule” of automotive engineering when it began development of the second generation Panamera: Never develop a new car, a new powertrain and a new factory simultaneously. So confessed Dr. Manfred Harrer, Vice President of Chassis Development.
But despite the transgression, the resulting technologies lift the latest Panamera into a new dimension of sedan capabilities, as previously reported (http://articles.sae.org/14896/). We now have full details of its powertrain, plus experience of how the most powerful, twin-scroll gasoline V8 performs on track.
Panamera owners who favor track-day activities will discover, as the author did, that 0-100 km/h acceleration comes in 3.4 s with the optional SportPlus via Launch Control. And they'll find that pulling 1.5 g in tight corners, as we did on the Lausitzring EuroSpeedway near Dresden, is no problem. Owners also should rest assured that the new Panamera has been extensively tested on the Nürburgring-Nordschleife circuit, achieving a lap time of 7 min 38 s, 14 s quicker than the previous generation Panamera.
Broadband cylinder deactivation
There are two new V8 and V6 gasoline units and a new Audi-sourced V8 diesel. An 8-speed PDK twin-clutch designed and developed by Porsche and built by ZF, replaces a 7-speed. In order to leverage scale within the VW Group, the new gas engines are expected to see future use in Audis, Bentleys, and potentially even a Lamborghini.
Criteria for the new engine lineup, as listed by Dr. Thomas Günther, Director of Powertrain, will not surprise SAE readers. The list includes lower fuel consumption and emissions; reduced weight; more efficient packaging; enhanced performance and that essential for all Porsches— the “right” aural signature. Modularity, to facilitate the flexibility demanded for hybrid variants, was also essential.
The Panamera's "halo" power unit is a new 4.0-L DOHC V8 with two twin-scroll turbochargers delivering a torque plateau rather than a curve: 770 N·m (568 lb·ft) from 1960 to 4500 rpm. Zero to 200 km/h (124 mph) takes a best 12.7 s. Fuel consumption for this version shows a 1.1L/100-km improvement to a best 9.3L/km and 212 g/km CO2 emissions. Claimed specific power is 137.5 hp/L versus 108.3 hp/L for the outgoing 4.8-L V8.
The longitudinally-mounted engine’s aluminum cylinder block is made using what Porsche engineers describe as “a special sand cast process.” The block weighs 39.1 kg (86 lb), a 6.7 kg (14.7 lb) reduction of mass versus the 4.8-L.
A new development of iron coating on the cylinder linings is used. Engineers describe it as being very highly wear resistant and durable. Wear is reduced by about a tenth at the motion reversal point of the piston rings, which have a chrome nitride coating. This should help with the high load changes generated by hybrid versions. An atmospheric plasma spray method is used to give a coating layer of 150 microns.
Mass reduction actions are evident throughout the block and include a crankshaft drive weight that weighs 1.4 kg (3 lb) less and uses an intermediate shaft to drive the water pump and timing drive. The switchable water pump has a toothed gear drive inside the engine which improves power unit packaging. Best weight reduction for the new V8 engines is 9.5 kg for the gasoline unit.
Packaging was also aided by a central turbo configuration, said Günther. The twin-scroll turbochargers, with counter-rotating turbines, have a maximum charge pressure of 0.3 bar (4.3 psi). Compact, isolated exhaust manifolds are fitted. Process air for the chargers is configured as a dual-branch system. It passes through intercoolers on each side of the engine, through one throttle valve on each side and into the left and right cylinder banks.
Fuel injectors are placed centrally in the combustion chamber. Fuel pressure is 250 bar (3626 psi) compared to the old engine’s 140-bar (2030-psi) injection system. The injectors have seven nozzles and each cylinder bank gets a high pressure pump.
Low friction lubricants are used throughout the engine. Oil consumption is said to have been reduced by up to 50%.
Broad-bandwidth cylinder deactivation
For high-g driving enthusiasts the new Panamera's oil circulation gets a lot of attention. Oil passages are partitioned into the oil supply for the engine and for the cylinder head. A fully variable vane oil pump is fitted with a valve controlling map-specific figures. An electronic switching valve located centrally in the V of the block controls piston spray nozzles. Churning losses are reduced and oil circulation volume controlled.
The Turbo has cylinder deactivation capability, a system increasingly used within VW Group. In 4-cylinder phases, fuel economy can be improved by up to 30%. Deactivation and reactivation of the cylinder is via Porsche’s VarioCam Plus, using a 2-stage sliding cam system. Under suitable load conditions, cylinder deactivation is available from 950 rpm to 3500 rpm with a 250-N·m (184 lb·ft) torque limit.
It is 30 years since Porsche introduced a twin-clutch transmission (PDK) into its race cars and into production models in 2008. The new PDK allows the car to achieve top speed in 6th, with the added two ratios providing overdrive. There is an 11.17 ratio spread against 10.2 spread with the previous 7-speed. The gearbox remains compact—in fact its “internals” are 142-mm (5.6-in) shorter than the 7-speed. It brings a claimed 1.4% fuel economy gain.
New 8-speed PDK and V8 diesel
We asked Michael Funk, PDK Project Manager, about the decision to plump for an 8-speeder not a nine. He replied, "It's right for us"—keeping in sync with the Panamera’s combination of performance and comfort.
Sourced from ZF, the PDK is package-protected for hybridization. It uses racecar-derived spray lubrication via a demand-based variable vane oil pump, claimed as a “first” for a road car. The gearbox uses a new oil, developed to reduce friction losses; full details were not yet released when this article was written.
Net weight reduction for the complete powertrain of the Panamera Turbo is 2.5 kg (5.5 lb), the 8-speed gearbox adding 7 kg (15.4 lb) compared to the 7-speed.
The newly developed 4.0-L V8 diesel is sourced from Audi but it has been tuned and adapted by Porsche. It replaces the previous Panamera’s 6-cylinder diesel and delivers 850 N·m (627 lb·ft) from 1000-3250 rpm—another broad plateau rather than a curve. It has a claimed output of 310 kW (415 hp). Similar to the gas V8, the diesel also has a central dual turbocharger configuration but these are sequential. The peak torque at 1000 rpm is achieved with only one turbo engaged. Both turbos have variable turbine geometry.
Sequential turbocharging is facilitated via variable valve timing of intake and exhaust valves. Axially sliding cam pieces on the camshaft are used to change switching positions, explained Dr. Günther. Electromagnetic actuators slide the cam pieces.
The diesel’s common rail system operates at 2500 bar (36.259 psi).
Best 0-100 km/h time with optional Sport Chrono Plus is 4.1 s; the 200 km/h dash takes 16.8 s. As an option, the car has a larger fuel tank of 90 L (23.9 gal) to provide 1475 km (916 mi) range potential.
V8 births a V6
The 2.9-L V6 makes the third Panamera power source and was designed in house by Porsche without VW involvement, engineers claim. It produces 324 kW (434 hp) at 5650 rpm and is rated at a claimed 550 N·m (406 lb·ft) from 1750 - 5500 rpm. Claimed performance figures include a best (with Sport Chrono package) 0-100-km/h time of 4.2 s.
The new V6 also has its two turbochargers tucked between the cylinder banks. The engine weighs 14 kg (31 lb) less than the previous car’s V6. Although similar in design to the V8 gasoline unit, the V6 has variable valve timing in both part- and high-load operation.Continue reading »