Much has changed in the automotive landscape since the previous tech feature on Porsche hybrids in the May 2015/#229 issue. Porsche has since launched its all-electric Taycan sedan (see the December 2019/#269 issue for more info). Also, continual government mandates for electrification of all new passenger cars by the 2030s have meant that automakers are scrambling to develop all-electric vehicle platforms. Even with recent advances in battery and charging technology, economies of scale have meant that it often takes years for these improved technologies to reach consumers.
With the obvious exception of 2020, Porsche’s global sales have increased year upon year, mostly thanks to their burgeoning lineup of four-door models. Because Porsche does not manufacture any small, ultra fuel-efficient vehicles (and thanks to the infamous VW “Dieselgate” scandal of 2015), they have increasingly turned to hybrid gasoline/electric vehicles to meet fleet average fuel economy and CO2 emissions standards in the U.S., EU, and elsewhere.
The current generation of Porsche E-Hybrid functionality was ushered in with the 2018 Panamera Turbo S E-Hybrid; an updated version of this vehicle based on the facelifted 971-generation Panamera is soon to debut as a 2021 model. Porsche’s E-Hybrid lineup has ballooned to three different versions of the Panamera E-Hybrid drivetrain configurations, each available in the three Panamera body style variants (standard four-door sedan, long-wheelbase Executive version, and Sport Turismo wagon). The current Cayenne E-Hybrid lineup launched for the 2020 model year and consists of a base E-Hybrid and a Turbo S E-hybrid version, each available in the standard and “Coupe” body style.
Previous Porsche E-Hybrid models used an Audi-sourced supercharged V6. The current crop of V6 and V8 engines are also based on an Audi design (see the September 2017/#248 tech feature for more information on these engines). However, Porsche was responsible for much of the development of these turbocharged powerplants, so they have the requisite Porsche sporting character.
The gasoline engines of the current Panamera and Cayenne E-Hybrid ranges match their gasoline-only counterparts: the base models use a 335-hp 3.0-liter V6 with a single turbocharger mounted in the valley between the cylinder heads. The Panamera range also features a mid-range 4S E-Hybrid with a 2.9-liter twin-turbocharged V6. The Panamera and Cayenne Turbo S E-Hybrid models use the 4.0-liter, 563-hp twin-turbo V8 that is also shared with Porsche’s corporate cousins at Audi, Bentley, and Lamborghini (for its Urus SUV).
All of Porsche’s current E-Hybrid models feature the Porsche Traction Management (PTM) all-wheel-drive system, but the Cayenne and Panamera diverge in the transmission department. The Cayenne SUV range retains the torque converter-equipped eight-speed Tiptronic gearbox with planetary gearsets, sourced from Aisin of Japan, while the current Panamera E-Hybrids adapt the eight-speed, dual-clutch PDK gearbox (the first Panamera E-Hybrid of 2013 used a Tiptronic gearbox).
In either case, the previous, hydraulically-actuated separating clutch (which used standard brake fluid to actuate a hydraulic slave cylinder) is replaced with a faster-acting electrically actuated clutch to couple and de-couple the “E-Machine” electric motor from the combustion engine as needed. The Tiptronic transmission of the Cayenne E-Hybrid models uses a unique configuration in which a dual-mass flywheel is bolted to the combustion engine’s crankshaft, with the clutch element between the flywheel and electric motor; the torque converter is sandwiched between the electric motor and the front of the transmission.
The torque multiplication factor of the torque converter of the Cayenne E-Hybrid’s Tiptronic transmission is the main reason why the Cayenne is rated to tow up to 7,716 lbs. This was a topic of consternation among U.S. owners of the previous 92A-chassis Cayenne E-Hybrid models—the factory towing package was not allowed in the U.S. market due to concerns about the tow hitch bar causing damage to the lithium-ion battery pack in the event of a severe rear-end collision. The current 9YA-gen Cayenne has been suitably fortified to minimize the chances of such damage and is available with a factory towing package in the U.S.
New Motor Design
The new E-Hybrid models use an external rotor motor design (with liquid-cooled stator) versus the previous internal rotor configuration. A conventional electric motor consists of a rotor (with embedded permanent magnets in the case of the Porsche design; see the April 2016/#235 Mission E tech feature for more info) turning inside a stator housing. An external rotor design has a cup-shaped rotor on the outside, with the stator windings in the middle. This allows a larger air gap area between the stator and rotor, enabling a greater amount of electromotive force to be generated compared to a similarly-sized internal rotor motor, along with greater torque potential, all in a more compact package. This enables an electric-only output of 134 hp and 295 lb-ft of torque, which can be applied almost instantly to augment the full power of the combustion engine.
Advances in battery cell technology allow the latest E-Hybrid battery pack to have 30 percent greater energy density than its predecessor while taking up the same amount of space. The new battery pack contains eight modules of 13 prismatic cells each for a total capacity of 37 Ah (up from 24 Ah of the previous E-Hybrid models), which results in an energy output of 17.9 kWh, and allows about 20 miles of electric-only range, depending on model and driving conditions. As with previous Porsche hybrids, the battery pack is mounted beneath the floor of the cargo area to keep the center of gravity as low as possible.
The E-Hybrid battery pack can be recharged via a standard 3.6 kW onboard AC charger, with an optionally available 7.2 kW charger (standard on Turbo S variants) to enable a full recharge of the battery pack from zero to 100 percent in 2.4 hours if a “Level 2” AC home electrical outlet is used (240 volts at about 30 amps). A standard, Level 1 U.S. household outlet would take twice as long at the same current output. In any case, the Porsche E-Hybrid models are not equipped to be used with a DC fast charger station as is their all-electric Taycan stablemate, as this would be largely superfluous with a plug-in hybrid model that can run on gasoline only if needed.
Hybrid Drive Modes
The ever-increasing advances in the hardware and software coordination of onboard vehicle systems allow for an array of hybrid driving modes, including some that are hyper-specialized to fit today’s world of city centers with electric-only zones.
E-Power: Operates on electric power only at up to 87 mph.
Hybrid Auto: The vehicle operates using a variable blend of electric and gasoline power, with the overall strategy designed to minimize fuel consumption. Like most hybrids, the Porsche E-Hybrids will start out in electric-only mode and blend in gasoline power as needed based on driver torque demand (as determined by an electronic “detent” in the accelerator pedal position sensor), vehicle speed, and battery state of charge.
The latest generation of E-Hybrids also incorporate the existing Porsche InnoDrive system of coordinating the drivetrain controls with the onboard GPS navigation system to optimize the efficiency of the powertrain according to topography and the layout of the road types and traffic conditions encountered during a journey. For example, an upcoming long downhill descent will prompt the system to allow more electrical energy to be used while ascending a hill because the downhill section will enable subsequent recharging of the battery pack.
E-Hold: This mode is selected by the driver to maintain the current state of charge of the battery. This is desirable in cases of traveling to a city center or other areas where only electric propulsion is permitted, with the battery charge reserved for such use.
E-Charge: Another driver-selectable mode in which the gasoline engine runs at all times to provide maximum charge to the battery pack.
Sport: The gasoline engine is always running in Sport mode. As with other Porsche models, the throttle response of the gasoline engine is quickened, as are the shifting speeds of the transmission, along with a more aggressive up- and downshifting strategy. Virtually all of the battery’s energy is available to boost the power output, and a more aggressive battery charging strategy is used while braking.
Sport Plus: In Sport Plus mode, the most aggressive shifting strategy is employed, and the full power of the electric engine is always available to augment the gas engine, except in cases where traction is limited as determined by the chassis control electronics (more about this below). The most aggressive energy recuperation mode is used while braking to rapidly recharge the battery pack while slowing. All of Porsche’s published maximum output figures and performance quotes are achieved in Sport Plus mode.
All of Porsche’s E-Hybrid models are equipped with Porsche Active Suspension Management (PASM) electronically adjustable dampers as standard; the basic Cayenne E-Hybrid comes with steel springs as standard, with adaptive air suspension available as a standalone option; all other E-Hybrid Porsches come standard with this three-chamber air spring system. The PASM and air suspension calibration of the 2021 Panamera E-Hybrid range is tuned to provide a wider spread between Normal and Sport Plus modes versus the previous version, which improves comfort over rougher surfaces. The updated PASM also allows the driver to soften the damping while in Sport Plus mode, which preserves the sharp throttle response and aggressive shifting maps of this mode while making it livable on rougher roads.
The basic Cayenne and Panamera E-Hybrid and the 4S version of the Panamera are available with Porsche Dynamic Chassis Control (PDCC) and rear-wheel steering as an option, with these systems being standard on Turbo S variants. As described in the #248 971 tech article, the PDCC uses an inverter to supply 48 volts to the actuators of the anti-roll bars to quell body roll of the 5,000+ lb vehicle. The rear-wheel steering system of the four-door Porsche models uses a single steering rack instead of the individual actuators of the sports cars. All of the above is orchestrated via Porsche’s “4D Chassis Control” system using a central chassis control unit operating via a high-speed data bus system to adjust any aspect of the chassis control system within milliseconds.
One of the biggest challenges of engineering any hybrid or fully electric vehicle is balancing the blend of braking from both the hydraulic service brakes and from deceleration provided by the electric motors as they generate electricity to recharge the battery. To compound the issue, Porsche offers three different types of braking systems with varying hydraulic piston sizes and frictions of coefficient, which meant that optimizing the brake pedal feel and modulation was a challenge for Porsche engineers. In a further effort to make the brake pedal feel of the updated 2021 Panamera E-Hybrid feel more natural, Porsche installed a brake master cylinder that allows for a slightly longer pedal travel.
The standard brakes on the basic models are steel rotors (360 mm front, 358 mm rear for the Cayenne, 390/365 mm for the Panamera) with Porsche’s now-customary acid green painted brake calipers (six-piston front, four-piston rear) as standard, though more discreet black paint is optional. The mid-level braking system is Porsche’s surface-coated braking system with its mirror-like tungsten-carbide surface coating and white-painted calipers (10-piston front, four-piston rear). The Turbo S E-Hybrid models come standard with Porsche’s lightweight PCCB brakes with massive 440 mm (17.3 in.) rotors in front, clamped by 10-piston calipers!
The Cayenne and Panamera E-Hybrid variants feature broadly similar interiors as their gasoline-only counterparts, but with a re-configured array of displays, which Porsche says is inspired by the 918 Spyder hypercar. The instrument cluster display can be configured to show energy consumption and recuperation, a visual aid to show when the gasoline engine starts up, and a 918-like “Boost Assistant” to show how much energy is available to assist the engine. The 12.3-inch central PCM display shows energy flow and consumption values much like any other gasoline-electric hybrid.