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Rear-wheel steering and cutting-edge chassis electronics make the ride in the next 7 Series more refined for the passengers in the back, and more dynamic and involving for the person behind the wheel. By Tristan Honeywill

Since taking over the Miramas Autodrome in Provence around 20 years ago, the importance of the test circuit has grown for BMW. Its 473 hectares can accommodate more than 300 BMW engineers testing up to 250 vehicles a day, as well as including on occasion the Sauber F1 cars. Its stable, almost rain-free climate means that testing schedules can go ahead as planned on most days.

But, arriving on a cloudless July day with the mistral blowing only the scent of lavender across the tracks, the speed bowl and handling circuits were almost deserted. Most of the prototypes had been locked out of the sight of journalists and the engineers confined to their desks while BMW used the facility to demonstrate the technology it will introduce on the next 7 Series luxury sedan.

The cars were pre-series versions, lightly disguised with black tape, their badges obscured. BMW was at pains to point out that production models will have better fit and finish but, stepping from the outgoing model into the new version, it was clear that the developers have created a much better car.

Project director Johann Kistler oversaw a series of presentations and driving exercises to explain and demonstrate the advances in the car’s active steering, which includes rear axle steering, and in its suspension, powertrain, human-machine interface and exterior design. “There are a lot of surprises in the driving experience, in active and passive safety and in the process of operating and controlling the car,” says Kistler. “And we’ve succeeded in creating the most efficient car in its segment.”

The clever chassis systems are designed to give the vehicle, 5.2m long in its stretched version, the handling of a much smaller car, while improving the ride comfort further. And dropping the traditional V12 for its top of the range model in favour of V8s and straight-sixes for the sake of fuel economy and CO2 emissions, BMW had to increase performance and smoothness.

It is traditional to treat these two areas more or less separately in development, but the greater integration of the electronic control in the 7 Series meant that the systems and the engineers behind them had to work far more closely than before. Bringing all the signals and commands together is a Flexray electronic architecture. “Flexray helps because we send a lot of information through the car from a lot of different sensors. To work well we need a very stable and quick data transfer system,” says Jos van As, director of functional development and integrated drive dynamics.

Unlike current CANbuses, the Flexray system synchronises all the control units’ clocks, allowing data to transmit quickly in an organised manner. A centralised control unit makes the calculations for all chassis functions. It allowed engineers much finer control of the ride and handling, combining signals from more than 16 chassis ECUs as well as the transmission and powertrain faster than before.

The result is a car that gives the driver more say as to how it rides and handles. The car has four basic set-ups that can be controlled by a switch next to the gear shift: comfort, normal, sport and sport plus. Each changes the characteristics of the front and rear steering, ESC-intervention, damping, traction control, throttle response and gear shifts.

Van As and his colleagues talked us through a methodical appraisal of them on several of the development tracks: high-speed slaloms and lane-change manoeuvres; around a cambered handling circuit with sprinklers providing different levels of friction; and another consisting of undulations, bumps and plain old-fashioned rough road.

The difference between the settings was easily appreciable. On the wet handling course, you could feel the car gently pull the back end straight in normal mode. In the sports modes, it is hard to believe that you are driving a luxury limousine. The rear steering system effectively shortens the wheelbase, making it feel like you are driving a 3 Series. The interventions are harder to discern and oversteer increases but the chassis performance remains linear, predictable and communicative.

Stretched out in the back of the long wheelbase version, comfort mode made a relaxation out of what should have been a nauseous experience over a rough undulating circuit.
Part of the reason for this is that the damping system is always active. Even when the dynamic stability control (ESC) is switched off, the active roll stabilisation programme adjusts the inbound and rebound stroke of the dampers independently of one another to suit the road conditions and the driving style. And active steering always stays on, albeit working to a different calibration.

It is also partly because of changes to the mechanical parts. The front suspension is a double-wishbone set-up that reduces steering disturbances from the very large tyres that can influence the kinematics of McPherson struts. “And by using a double wishbone the damper no longer needs to guide the wheel,” says van As. “This separation of functionalities means you can use thinner piston rods for the damper that lowers the friction and improves the ride. We also tuned the bushes so their stiffness differs in different directions. It helps isolate the rolling noise of the tyres from the cabin.”

The rear steering system was developed in partnership with Magna Steyr, although Continental has demonstrated a similar system. An electric gear can adjust the direction of the rear wheels by up to 3°. At low speeds they turn against the angle of the front to reduce the turning circle by up to 70cm. “Anybody who’s ever manoeuvred a large car in an underground garage will appreciate this feature makes life a lot easier,” says Kistler.

At around 60km/h they follow the front wheels. Changing lanes on the highway thus produces significantly lower yaw rates, much more comfortable for the person travelling in the back.

“We think 3° is the optimum,” says van As. “It’s enough to give a significant improvement to the turning circle and at high speeds 3° is a lot. If you want to move the rear wheels more, the packaging requires greater care – the rear wheel arches must get bigger to allow the tyre to move more.”

Making the 7 Series a better place in which to cover long distances also means upgrades to its interior and driver assistance systems. In the longer term, BMW expects a sizeable chunk of its business to come from providing its drivers with telematic services. The 7 Series is already starting to present more information, and developers have considered how to present this more effectively. The car uses black panel technology for instrument cluster behind the wheel. Made up of a high-resolution colour display, when the car is off, the screen is a plain black panel. When driving, it displays whatever information is required for the situation.

At 10.2-inches, the central display is bigger, higher resolution and uses a list structure instead of the former compass arrangement. Effort has gone into making the iDrive controller more intuitive. And other features include a night-vision system that warns of potential collisions with unseen pedestrians and a road sign recognition system designed to eliminate those moments of nagging doubt when you are being overtaken but are unsure whether they are speeding.

There was no time, however, to test and scrutinise these technologies. The fleet of black E66 7 Series were waiting to get the journalists back to the airport, but mainly just out of Miramas. There were still four or five hours of sunlight left, and the engineers were keen to get their prototypes back out on the tracks.

Project director Johann Kistler on the 7 Series:

"In active and passive safety, and in the process of operating and controlling the car, we have made great progress. We have succeeded in creating the most efficient car in its segment in the
market.

"The new BMW 7 Series comes as standard with our new Dynamic Damper Control including Dynamic Driving Control.
With this new technology, the newly developed dampers adjust infinitely in the inbound and rebound stroke to both road conditions and your style of motoring preventing unwanted movements of the car caused by bumps or fast lateral acceleration operating independently of one another to prevent undesired movements of the car caused by bumps or fast lateral acceleration.

"The dampers, gearshift dynamics as well as the gas pedal and steering assistance control maps are varied by the Dynamic Driving Control button on the centre console, offering the driver the three stages COMFORT, NORMAL and SPORT.
There is also a special traction mode and the SPORT+ setting with reduced intervention by DSC – or the option to switch off DSC altogether – for a particularly sporting driving experience.

"The car‘s suspension systems are combined perfectly with one another through ICM Integrated Chassis Management. This high-performance electronic control system analysing numerous
sensor signals to monitor the car‘s driving behaviour is able to harmonise the drivetrain and suspension functions with one another in fractions of a second, ensuring maximum stability under all conditions.

"Integral Active Steering controls the steering angle both
front and rear. At low speeds the rear wheels are turned against
the steering angle of the front wheels to give the BMW 7 Series a significant improvement of agility.

"Depending on how fast you are travelling, the car‘s turning circle is reduced by up to 70 centimetres. At higher speeds it
gives the car a more comfortable reaction when changing lanes and in bends. This will be appreciated above all by the
passengers at the rear now no longer experiencing any abrupt sideward movements.

"We have also fundamentally upgraded all of the engines, now offering the world‘s most efficient V8 petrol engine, the most powerful straight-six within BMW‘s entire range of engines, and the first representative of a new generation of straight-six
diesel engines.

"In their respective performance class, all of these power units offer an unparalleled balance of power, performance and economy. So this applies to all three engines in the 730d, the 740i and the 750i, which fulfil all EU5 emission requirements.

"The first representative of a new generation of six cylinder
diesel engines is making its world debut in the BMW 730d.

"Brand-new from the ground up, this engine offers even more power on even less fuel and lower emissions. It therefore consistently implements the BMW EfficientDynamics development strategy.

"Displacing 3.0 litres, the new six-cylinder diesel develops maximum output of 180 kW/245 hp. Compared with its predecesor, the new BMW 730d offers 10 kW/14 hp more power on 10 per cent less fuel.

"The new BMW 740i is powered by the most powerful straight-six in BMW‘s wide range of engines. On the latest version of BMW‘s 3.0-litre straightsix, maximum output has been increased to 240
kW/326 hp through specific modifications on the turbocharger system.

"In developing superior power and performance, the straight-six with Twin Turbo and High Precision Injection achieves a standard provided in the past only by much larger eight-cylinder
power units.

"Compared with its predecessor, the new 740i offers 15 kW/20 hp more power and, at the same time, 12 per cent lower fuel consumption.

"Our new eight-cylinder petrol engine with Twin Turbo technology and High Precision Injection is already well-known to you from the BMW X6.

"An absolute innovation in technical terms is the arrangement of the tubochargers and the catalytic converters in the V-section between the two rows of cylinders never seen before on an eightcylinder petrol engine. This allows an unusually compact configuration of engine components and, at the same time, made it necessary to re-position the intake and exhaust ducts.

"The new 750i eight-cylinder power unit enters a power range so far only offered by twelve-cylinder engines. So we are indeed quite willing to compare this power unit with the current 760i right at the top of the BMW 7 Series. And at the same time we are reducing fuel consumption on the eight-cylinder by almost 15 per cent, applying the fuel consumption level allowed under the EU5 standard."

Automotive Engineer will have more on the 7-Series later this year.