BMW Provides Update on ActiveHybrid X6
09 November 2009
|Output and torque diagrams, BMW ActiveHybrid X6. Click to enlarge.|
BMW has provided some additional detail on its two-mode ActiveHybrid X6, as well as updating some of the figures released for the introduction of the production model at the Frankfurt Motor Show in September. (Earlier post.) The ActiveHybrid X6 arrives in US BMW Centers in the fourth quarter.
The ActiveHybrid X6 is BMW’s first application of the two-mode transmission developed in partnership with GM and then-DaimlerChrysler, and offers approximately a 20% reduction in fuel consumption versus a comparable vehicle powered by a combustion engine alone, while at the same time offering an increase in driving dynamics.
|Components of the ActiveHybrid X6. Click to enlarge.|
The drive system in the BMW ActiveHybrid X6 consists of a 4.4-liter 300 kW/407 hp V8 power unit (revised upward slightly from introduction) with BMW TwinPower Turbo Technology and two electric motors developing 67 kW/91 hp and, respectively, 63 kW/86 hp. Maximum system output is 357 kW/485 hp, peak torque is 780 N·m/575 lb-ft.
Acceleration from a standstill to 100 km/h comes in 5.6 seconds (0.2 seconds longer than preliminary figures). Top speed of the BMW ActiveHybrid X6 is limited electronically to 236 km/h or 146 mph (250 km/h or 155 mph with the optional Sports Package). Average fuel consumption in the EU5 test cycle is 9.9 liters/100 km (equivalent to 23.8 mpg US mpg), with a CO2 emission rating of 231 grams/kilometer.
BMW’s first full hybrid model is able to run exclusively on electric power up to a speed of 60 km/h or 37 mph, with the combustion engine being activated automatically whenever required.
The two-mode active transmission provides combinations of the two power modes for enhanced efficiency and dynamic performance at all times. With the two electric motors, three planetary gearsets and four multiple-plate clutches, drive power is transmitted through a seven-gear automatic transmission operated by the driver via an electronic gear selector lever and, respectively, shift paddles on the steering wheel.
V8 with TwinPower Turbo Technology. The 4.4-liter V8 was terms presented for the first time in the BMW X6 xDrive50i. The world’s first V8 gasoline engine with two turbochargers and two catalytic converters in the V-section between the two rows of cylinders maintains its maximum output of 300 kW/407 hp from 5,500 – 6,400 rpm. Torque peaks at 600 N·m/ 442 lb-ft in the speed range between 1,750 and 4,500 rpm.
With BMW TwinPower Turbo Technology four cylinders are each supplied with compressed air by one turbocharger for a particularly spontaneous and direct response to the gas pedal. Engine power builds up without delay, continuing all the way to high engine speeds.
The innovative arrangement of the turbochargers also benefits the response of the engine, the new position of the intake and outlet ducts helping to keep the intake pipes and manifolds shorter and provide larger cross-sections significantly minimizing pressure losses on both the intake and exhaust side.
High Precision Injection developed by BMW ensures precise dosage of fuel at all times. In the same process the cooling effect of the fuel injected directly into the engine allows a compression ratio exceptionally high on a turbocharged engine, further enhancing the efficiency of the V8 power unit.
Piezo-injectors positioned in the middle between the valves help to make the combustion process particularly smooth, efficient and clean, the V8 power unit therefore fulfilling both the European EU5 standard and the ULEV II standard in the USA.
Compared with the BMW X6 xDrive50i, the power unit has been modified in a number of its features to meet the specific requirements of the BMW ActiveHybrid X6.
There is no longer a conventional starter, just as the alternator and belt drive for the a/c compressor and the hydraulic pump on the power steering have both been dropped. The main and secondary coolant circuit, in turn, have been modified for all-electric motoring, and a heat insulation plate protects the power electronics additionally from excessive temperatures.
The position of the oil filler manifold has been modified, the conventional torque converter is replaced by a two-mass flywheel, and the exhaust system has been modified for an optimum acoustic effect when the combustion engine fires and cuts in in the all-electric mode.
Two-Mode Active Transmission. The Two-Mode Active Transmission with its fully integrated electric motors is the central unit in the drive system featured in the BMW ActiveHybrid X6. Developed specifically by BMW for its first full hybrid vehicle, the Two-Mode Active Transmission ensures optimum interaction of the combustion engine and electric drive in the interest of maximum power and efficiency at all speeds.
In its dimensions, the transmission is virtually identical to a conventional automatic transmission and is arranged directly behind the combustion engine. Following the principle of an ECVT Electric Continuously Variable Transmission, the Two-Mode Active Transmission provides the mechanical connection between three planetary gearsets and four multiple-plate clutches in a configuration allowing the power split required for the drive power coming from the combustion engine and the electric motors in two transmission ranges and therefore ensuring unique variability in the combination of the two power sources conventional hybrid drive is not able to offer.
One of the two transmission modes is specifically for setting off and accelerating at low speeds, the second is for driving at higher speeds under optimum conditions. When setting off only one electric motor is activated at the beginning, enabling the BMW ActiveHybrid X6 to drive under electric power alone up to a speed of 60 km/h or 37 mph.
As soon as the driver requires more power, the second electronic motor automatically fires the eight-cylinder power unit and subsequently acts as a generator providing a permanent flow of electric power. The combustion engine is automatically added to the power flow in accordance with the driver’s requirements and the level of performance needed, and is cut off by the electronic control unit when coasting at speeds below 65 km/h or 40 mph.
Power is transmitted by the Two-Mode Active Transmission acting as a seven-speed transmission operated by the driver by means of an electronic gear selector lever on the centre console. As an alternative to the automatic mode, the driver may also opt for manual selection of gears, shifting up and down either sequentially by moving the gear selector lever appropriately or by using the gearshift paddles featured as standard on the steering wheel of the BMW ActiveHybrid X6.
Electric motors The two electric motors offer almost the same degree of power but have been modified in their performance characteristics as a function of their specific purpose and application. Their output is 67 kW/91 hp and, respectively, 63 kW/86 hp, with peak torque of 260 N·m/192 lb-ft and, respectively, 280 N·m/206 lb-ft.
Maximum system output developed jointly by the combustion engine and the two electric motors is 357 kW/485 hp, with combined torque of 780 N·m/575 lb-ft. This makes the BMW ActiveHybrid X6 the world’s most powerful production light-duty hybrid.
High-performance battery pack with separate liquid cooling systems. The electric motors receive their energy from a nickel-metal-hydride (NiMH) high-performance battery pack fitted beneath the floor of the luggage compartment and feeding power also to the vehicle’s on-board network.
Even with the combustion engine switched off, this maintains all electrically operated functions including the automatic air conditioning, with electric power generated through the recuperation of brake energy. To perform this function the electric motors serve as a generator in overrun and when applying the brakes in order to feed electric power generated on no extra fuel into the storage units.
The battery in BMW ActiveHybrid X6 has a capacity of 2.4 kWh, with 1.4 kWh being used actively for running the vehicle. To provide the power required, the high-voltage direct current coming from the high-performance battery is converted into three-phase alternating current for the two electric motors. The maximum power available for a period of three seconds is 57 kW, the control unit for the NiMH battery serving to permanently measure and determine various data such as the power currently available and the charge level.
The high-performance battery comes with its own liquid cooling system incorporating a heat exchanger to cool the battery both through outside air and, additionally, through the coolant circuit in the air conditioning. Both circuits are activated as required either individually or in an appropriate combination, the control unit choosing the most effective and efficient cooling option as a function of ambient temperature and the temperature of the high-performance battery.
The cooling function using the vehicle’s air conditioning is activated by an appropriate switch valve, the electrical a/c compressor is activated automatically as required, with the interior and the battery being cooled independently of one another.
This ensures much more efficient cooling than with systems cooled by air alone, helping to make the energy storage unit significantly more efficient and maintaining the hybrid functions longer both under extreme weather conditions and whenever the driver prefers a particularly sporting style of motoring.
Power electronics for highly efficient energy management. Power electronics developed especially for BMW ActiveHybrid serves to keep energy management on board the BMW ActiveHybrid X6 both efficient and flexible. The most important parameter for determining and controlling the operating strategy is the charge status of the battery pack storing electrical energy generated through the recuperation process.
The power electronics also mastermind the charge process of the battery pack during recuperation, alternating current generated by the generators through Brake Energy Regeneration being converted into direct current subsequently fed into the battery.
Recuperation using energy released when applying the brakes. To generate the electric power stored in the battery pack, the BMW ActiveHybrid X6 uses an upgraded version of the Brake Energy Regeneration already featured in BMW’s current models running on a combustion engine alone. In overrun and when applying the brakes, the electric motors act as generators feeding power into the high-performance battery.
Depending on the stopping power applied, this task of recuperating brake energy is performed either by one or both of the electric motors. The output generated in the generator mode of approximately 50 kW is about 25 times higher than the energy supplied so far by Brake Energy Regeneration.
Generator mode providing electric brake power. In addition to these features, the two electric motors provide a major share of the brake power required by the vehicle when operating in the generator mode. The electrical brake system is able to provide up to 3 m/sec2 or, respectively, 0.3 g of brake power in the purely recuperative mode, thus taking a significant burden off the mechanical brake system.
Hybrid technology in the BMW ActiveHybrid X6 serves to convey brake power through the xDrive powertrain to all four wheels, thus benefiting from the stopping power provided by the electric motors in the recuperative mode. And whenever the stopping power required exceeds the level of 3 m/sec2, the control unit, interacting with the active brake servo, generates additional brake power through the mechanical brakes.
Electronic Power Steering. The BMW ActiveHybrid X6 is the first BMW X Model to feature EPS Electronic Power Steering for active steering assistance both when running on the combustion engine and in the all-electric mode.
EPS Electronic Power Steering on the BMW ActiveHybrid X6 is combined with integrated steering assistance related to road speed (Servotronic). EPS significantly reduces the energy required in comparison with conventional, hydraulic power steering, since this electronic system is activated only when power assistance is really required or is desired by the driver. When driving straight ahead, therefore, the electric motor does not take up and consume any energy, thus serving to reduce fuel consumption to an even lower level.
Hybrid-specific Auto Start Stop. The BMW ActiveHybrid X6 features a new generation of the Auto Start Stop function adapted to the specific requirements of a hybrid and at the same time operating with a significantly greater level of comfort.
The combustion engine is switched off automatically when stopping at a road junction or traffic lights. During the short periods in which the combustion engine is switched off (and while driving under all-electric power), all the electrically operated functions of the vehicle remain fully operative, the on-board network receiving an ongoing supply of power from the high-performance battery. The electrical a/c compressor, for example, maintains full climate control of the passenger compartment and other electrical power-consuming items such as the lights and entertainment systems likewise remain fully available even with the combustion engine switched off.
Graphic presentation of hybrid drive functions. Two displays in the cockpit of the BMW ActiveHybrid X6 provide information on the current operating status of the hybrid system. The most important information is presented in the central instrument cluster, clearly separated according to the different drive modes. Further information and technical explanations, in turn, are provided in the Control Display on the centre console.
That's pretty strong regen for a small battery.
Posted by: clett | 09 November 2009 at 07:28 AM