|Panamera S E-Hybrid PHEV on the road. Click to enlarge.|
During an international press event in Germany, in which more than 42 test drives were conducted with journalists in the Panamera S E-Hybrid (earlier post) covering a total distance of more than 1,200 kilometers (746 miles), the new plug-in hybrid model consumed 4.4 l/100 km (53.4 mpg US) averaged over all drives.
The lowest fuel consumption value recorded on the circuit course for the Panamera plug-in hybrid was 2.8 l/100 km (84 mpg US). NEDC testing indicates combined cycle fuel consumption of 3.1 l/100 km (75.9 mpg US) for the PHEV, with accompanying CO2 emissions (combined) of 71 g/km. Electrical consumption (combined) is rated at 162 Wh/km.
|Layout of the plug-in hybrid powertrain. Click to enlarge.|
The test drive results were obtained from four unmodified Panamera S E-Hybrid production cars, each carrying three to four people, with the climate control system activated and accelerating up to 230 km/h (143 mph) on the highway section of the route.
The test circuit, which had a total length of 28.7 km (17.8 miles), followed a course through and around the city of Hockenheim and comprised 6.5 km (4.0 miles) city driving, 9.2 km (5.7 miles) of country roads and 13 km (8 miles) of German Autobahn—some without speed limits.
A prerequisite for attaining such fuel consumption values is systematically exploiting opportunities for charging the 9.4 kWh lithium-ion battery on the electrical grid, Porsche noted.
The car’s range of 36 kilometers (22.4 miles) in all-electric driving was also confirmed in practice with a fuel consumption value of 0.0 l/100 km and zero local emissions, which was not only attainable in NEDC testing on a dynamometer, but also on the street. The car attains this value at an average speed of 54 km/h (33.6 mph), while the average speed in NEDC testing is just 33 km/h (20.5 mph).
Powertrain. The Panamera S E-Hybrid features a new Euro 6-compliant turbocharged 3.0L direct-injection V6 engine that delivers 245 kW (329 hp) of power and 440 N·m (325 lb-ft) of torque; three-phase 70 kW synchronous motor developing maximum torque of 310 N·m (229 lb-ft); an 8-speed Tiptronic S transmission with Normal and Sport shifting programs and a separate shifting strategy for E-Power mode; and a 9.4 kWh Li-ion battery pack.
The Panamera S E-Hybrid offers a combined system power of 416 hp (306 kW), accelerates from zero to 100 km/h in 5.5 seconds and has a top speed of 270 km/h (168 mph). The electric drive produces 95 hp (71 kW), with maximum torque of 310 N·m (229 lb-ft).
The Panamera S E-Hybrid offers multiple modes that can be selected by pushbuttons on the center console. The E-Power mode—activated by default, provided that the battery charge state is sufficient—enables largely all-electric driving.
The total system power can be accessed at any time by kickdown, such as to overtake another vehicle. In this case, the E-Power mode remains activated in background, and it enables all-electric driving as soon as acceleration returns to a moderate level, and the electric top speed is not exceeded.
When E-Power is deactivated, the operating strategy switches to Hybrid mode. This operating strategy—programmed for efficiency—fully automatically switches between the driving states of electric driving, hybrid driving with load point shift, coasting, electrical system recuperation and boosting.
Here the E-Power Assistant, which the driver can select in the instrument cluster’s TFT display, can precisely meter, based on the display, whether the car is driven all-electrically or with support of the combustion engine. Essentially, the system “reserves” the battery’s available energy capacity for later electric driving phases by switching to Hybrid mode and engaging the six-cylinder engine earlier.
The E-Charge mode is a newly developed driving mode that is activated by a pushbutton on the center console. It charges the high-voltage battery during the drive. Here, the electric motor acts as a generator, which increases load on the combustion engine until the engine is operating in very efficient load ranges. This energy is stored in the traction battery so that it will be available for later zero-emissions driving.
This mode increases the car’s electric range on drives with a high proportion of combustion engine use—e.g. on highway drives that are followed by a route through the city. In other words, the battery can be charged during the motorway driving, so the city route can be driven all electrically. In stop-and-go traffic within the city, battery charging is reduced for efficiency reasons to preserve typical hybrid characteristics in E-Charge mode as well, such as shutting off the combustion engine when the vehicle is stopped and slow electric drive-off.
As in the previous conventional hybrid model, the brake system of the new Panamera S E-Hybrid enables recovery of braking energy. The generator function of the electric motor might be activated first, absorbing up to the maximum possible load, then the conventional brake would be superimposed, depending on how hard the driver presses the brake pedal. This battery regeneration map differs from that of the previous hybrid, and was adapted to the new electric motor that is more powerful, and it was further optimized for driveability and pedal feel.
Rounding out the driver’s options is the Sport mode for typical Porsche high performance and a special sporty characteristic with more direct handling.
Motor and battery. At 95 hp (70 kW), the newly developed electric motor is 48 hp stronger than the motor in the previous model—peak power has more than doubled. Since its weight remained nearly constant, this improved the power-to-weight ratio of the electric motor from 1.1 kg/kW to 0.54 kg/kW.
Maximum torque increased ten-fold to 310 Nm. This performance increase of the three-phase synchronous motor is attributable to a modified number of windings on the coils and an increased voltage level. A different magnetic material was used in the electromagnetic circuit as well, and an optimized cooling channel geometry improves the motor’s thermal resistance.
|Evolution of Porsche hybrid modules|
|Cayenne and Panamera S||Panamera S
|Planned next-gen module|
|Max power||34 kW||70 kW||>95 kW|
|Max torque||300 N·m||310 N·m||ca. 400 N·m|
|Nominal voltage||288 V||384 V||n/a|
|Power-to-weight ratio||1.1 kg/kW||0.54 kg/kW||<0.50 kg/kW|
|Max engine speed||6700 rpm||6700 rpm||9000 rpm|
|Transmittable engine torque||600 N·m||600 N·m||900 N·m|
These modifications are roughly equivalent to a power increase attained by increasing the displacement of a combustion engine and introducing high-performance cooling, Porsche said.
The newly developed electric motor is subjected to far greater stresses than before. For example, the E-Power mode demands quick response with high peak powers and high thermal resistance of the electric motor. High electrical system recuperation performance must be assured in all driving modes. The driver can summon extended boost phases up to the car’s top speed in Sport mode and by kickdown.
The new E-Charge mode poses the most stringent requirements. During charging phases with their high torques that are optimal for efficiency subject the electric motor to high stresses while it operates as a generator. However, the electric motor’s peak power must remain accessible for E-Power mode. In addition, it is necessary to assure comfortable and quick restarting of the combustion engine and the supply of electricity to the vehicle electrical system.
The performance partner which stores energy for the electric motor is a newly developed 384V Li-ion battery. With a capacity of 9.4 kWh, it offers five times the storage capacity of the NiMH battery in the previous conventional hybrid model, yet it does not require any additional installation space. Like before, it is integrated in a space-saving location under the trunk floor.
|Decoupler with actuator mechanism. Click to enlarge.|
Decoupler with extended tasks. A key drivetrain component of the parallel full hybrid is the clutch between the combustion engine and the electric motor. The drive system always chooses the starting sequence that best satisfies driver wishes while taking into account comfort and dynamics. Multiple processes run simultaneously in the starting phase.
When the combustion engine is coupled, the lock-up of the torque converter in the automatic transmission disengages, and the torque of the electric motor is briefly increased to start the six-cylinder engine. Simultaneously, the clutch between the electric motor and the combustion engine engages with a defined pressure characteristic. Along with the well-engineered interplay of combustion engine and electric motor, the spindle actuator of the clutch control unit supplies the hydraulic pressure needed to activate the clutch.
The layout of the decoupler for the Panamera S E-Hybrid was adopted from the previous model. The system consists of a friction disc with torsion damper and pressure plate with integrated central release mechanism. It is completed by the flywheel that is integral to the crankshaft. Its operating states have changed due to the extended functionality of the Panamera S E-Hybrid.
For example, the significantly larger battery capacity and power-enhanced electric motor have resulted in longer electric driving periods and fewer combustion engine restarts. These modified requirements made it necessary to extend the software for control of the decoupler system.
All of this places high requirements on the components and the control system. The Hybrid Manager coordinates the interplay between combustion engine, electric motor with decoupler and transmission. Conditions of the high-voltage system are also considered here, such as temperature and the battery charge state. They are continually monitored by the Battery Management System, which communicates with the Hybrid Manager.
Combustion engine with extended operating strategy. The primary drive source is the 3.0L engine. Fuel economy was significantly improved by using an optimized thermal management system to distribute heat more precisely and a further developed operating strategy with intelligent control of catalytic converter heating.
After the vehicle has been parked at freezing temperatures overnight, for example, an electric cold start is now possible down to an engine oil temperature of zero degrees Celsius. Previously, this limit was 15 degrees Celsius. The starting sequence was also improved to make the power of the combustion engine available to the driver even faster when the accelerator is pressed after electric driving. Many of the auxiliary systems are now electric as well to guarantee their functionality during all-electric driving.
8-speed Tiptronic. Porsche relies on the proven Tiptronic S for power transmission. It was possible to use the eight-speed automatic transmission without component modifications in the Panamera S E-Hybrid, despite higher shares of electrical system recuperation and the power-enhanced electric motor. However, the control system for the transmission was fundamentally redesigned, and it was extended to perform additional functions.
In E-Power mode, for example, a special shifting strategy was implemented based on the modified electric motor characteristic. Unlike Hybrid mode, it utilises a higher rev level over the entire relevant speed range for optimal efficiency. These changes have resulted in different torque relationships in the lock- up torque converter. Therefore, transmission control was extended for the restart process. For the Sport mode, a hybrid-specific, emotionalized gear shifting strategy is also stored in the control unit. In this case, gear selection always assures the best possible balance of longitudinal dynamics, acoustics and fuel economy.
|Coolant loops in the Panamera S E-Hybrid. Click to enlarge.|
Two coolant loops. To realize their full performance and efficiency capabilities, the components of the hybrid drive need different but precisely defined operating temperatures. Therefore, requirements for the coolant loop in the new Panamera plug-in hybrid have been increased compared to the previous model. Along with the high-temperature loop for the combustion engine and electric motor, two low-temperature circulation loops in the Porsche Panamera S E-Hybrid assure efficient cooling over all relevant operating ranges.
For example, the coolant supply to the electric motor was optimized to significantly reduce temperature levels, especially in E-Power mode. Along with optimal positioning of the temperature sensor in the coolant flow, this permits precise control of the active electric motor components.
The two intercoolers and the power electronics were integrated in the previous low-temperature circulation loop. The new second temperature loop is exclusively designed for thermal management of the lithium-ion battery. When the battery’s temperature exceeds a certain value, it can also be cooled by a heat exchanger in the cooling loop. Moreover, an electric heating element (PTC heater) integrated in the battery housing assures functionality of the energy storage device down to the Arctic temperature range.
|Next-generation hybrid module with air cooling to supplement water-cooling. Click to enlarge.|
Next-generation hybrid module: more power, new cooling strategy. The next generation of the Porsche hybrid drive has already attained a very advanced development level. Project specifications call for an electric motor which has more than one-third more power than that of the Panamera S E-Hybrid with more than 95 kW of power; its torque also increases by just around 30%. This leads to greater needs to remove heat, which is necessary during high and long-duration power output.
Porsche engineers developed a new cooling strategy, in which the stator—the stationary exterior part of the electric motor—is still water-cooled, as before. However, the coils of the inner rotating part are air- cooled. This is accomplished by a blower wheel that draws in outside air via an air channel with flow distributor.
The heat is rejected via a large number of channels integrated in the housing. This solution guarantees uniform flow distribution and cooling of the coils for maximum electric performance, and it combines high levels of integration density and optimal package utilization, the company said.
The new Panamera S E-Hybrid will be at dealers starting 27 July 2013.