BMW designed the i8 from the start as a plug-in hybrid sports car boasting agile performance attributes and extraordinary efficiency. The LifeDrive architecture—developed specifically for the BMW i brand—offers an ideal platform for a weight-minimizing construction, low center of gravity and even weight distribution. The combustion engine and electric motor, battery pack, power electronics, chassis components, and structural and crash functions are all arranged within the aluminum Drive module, while the central element of the Life module is the i8’s CFRP (carbon fiber reinforced plastic) passenger cell. This structure also allows a considerable degree of design freedom, which has been utilized—within the framework of the design language developed for BMW i—to give the BMW i8 its distinctive appearance.

Powertrain and driving experience. The plug-in hybrid drive system of the BMW i8 comprises a BMW TwinPower Turbo engine combined with BMW eDrive technology. The BMW Group has developed not only the internal combustion engine and electric motor in-house but also the power electronics and the battery.

Rear-mounted 3-cylinder engine. Click to enlarge.		Front-mounted eDrive. Click to enlarge.

This bespoke plug-in hybrid system, developed and produced by the BMW Group, enables a range in everyday driving of up to 35 kilometers (approx. 22 miles) and a top speed of 120 km/h (approx. 75 mph) on electric power alone, coupled with an all-wheel driving experience headlined by powerful acceleration and a dynamically-biased distribution of power through enthusiastically taken corners.

The BMW i8 is the first BMW production model to be powered by a three-cylinder gasoline engine. The three-cylinder, 1.5-liter combustion engine develops 170 kW (231 hp) and torque of 320 N·m (236 lb-ft) and drives the rear wheels. The specific output of 113 kW/154 hp per liter of displacement is on a par with other high-performance sports car engines and is the highest of any engine produced by the BMW Group.

The new three-cylinder engine derives its typical characteristics from BMW’s inline six-cylinder engines, to which it is closely related. The three-cylinder’s BMW TwinPower Turbo technology comprises a high-performance turbocharging system and direct gasoline injection with high-precision injectors positioned between the valves, along with VALVETRONIC throttle-less load control, which improves efficiency and response thanks to seamlessly variable valve lift control.

BMW i8. Click to enlarge.

Like a six-cylinder engine, the three-cylinder unit is free of first and second-order inertial forces. The low roll torque, a typical feature of a three-cylinder design, is further reduced by a balancer shaft, while a multi-stage damper integrated in the automatic transmission ensures very smooth and refined running at low rpm. BMW TwinPower Turbo technology and low internal friction improve both fuel consumption and torque characteristics. Accelerator response is sharp and the three-cylinder unit quickly reaches its maximum torque of 320 N·m.

The electric motor draws its energy from a lithium-ion battery, which can be charged from a conventional 110 volt power outlet as well as a 220 volt electric vehicle charger, and sends its power to the front axle.

The car’s second power source is a 96 kW (131 hp) hybrid synchronous electric motor specially developed and produced by the BMW Group for the BMW i8. The motor produces maximum torque of around 250 N·m (184 lb-ft). Credit for the linear power delivery, which extends right up to the high end of the rpm range, goes to a special hybrid motor design principle exclusive to BMW i. BMW eDrive technology refines and improves on the principle of the permanently excited synchronous motor with a special arrangement and dimensions for the torque-producing components. This results in a self-magnetizing effect normally confined to reluctance motors. This additional excitation ensures that the electromechanical field generated when current is applied remains stable even at high rpm. (Earlier post.)

As well as providing a power boost to assist the gasoline engine during acceleration, the electric motor can also power the vehicle by itself. lithium-ion battery powering the motor is centrally mounted underneath the floor of the vehicle. This model-specific version of the high-voltage battery was developed and produced by the BMW Group. It has a liquid cooling system, offers a maximum usable capacity of 5 kWh and can be recharged from a conventional 110 volt power outlet, at a BMW i charging station, or at a public EV charging station.

BMW i8. Click to enlarge.

When power demands allow, the high-voltage battery is recharged by the electric motor. The high-voltage starter-generator, responsible for starting the combustion engine, can also be used as a generator to charge the battery, the necessary power being provided by the BMW TwinPower Turbo engine. These various processes help ensure that the BMW i8 always has sufficient energy on board to power the electric drive system. The all-electric driving range is sufficient to cover most urban driving requirements. Out of town, the BMW i8 delivers impressively sporty performance with extreme efficiency, due to the electric motor’s power-boosting support for the gasoline engine.

The rear wheels of the BMW i8 are driven by the gasoline engine via a six-speed automatic transmission, while the front wheels receive their power from the electric motor via a two-stage automatic transmission. Combined maximum output is 266 kW/362 hp and combined peak torque of 570 N·m (420 lb-ft).

The BMW i8’s intelligent powertrain control system coordinates both power sources. The BMW i8 has an electronically controlled top speed of 250 km/h (155 mph), which can be reached and maintained when the vehicle operates solely on the gasoline engine.

Variable front-rear power splitting in line with changing driving conditions enable excitingly dynamic cornering. On entering the corner, the power split is biased towards the rear wheels to improve turning precision. For more vigorous acceleration out of the corner, the powertrain controller returns to the default split as soon as the steering angle becomes smaller again.

The BMW i8 offers the driver unusual scope to adjust the drive and suspension settings of the vehicle in order to adapt the driving experience to his or her individual preferences. As well as the electronic gear selector for the automatic transmission, the driver can also use the Driving Experience Control switch—a familiar feature of the latest BMW models—or, exclusively to the BMW i8, the eDrive button. It gives the driver five operating modes to choose from: D for automated gear selection in COMFORT and ECO PRO modes, SPORT mode and eDrive for pure-electric driving—likewise with a choice of COMFORT and ECO PRO mode.

The Driving Experience Control switch on the center console gives drivers a choice of two settings. On starting, COMFORT mode is activated, which offers a balance between sporty performance and fuel efficiency, with unrestricted access to all convenience functions. Alternatively, at the touch of a button, ECO PRO mode can be engaged, which, on the BMW i8 as on other models, supports an efficiency-optimized driving style.

The powertrain controller coordinates the cooperation between the gasoline engine and the electric motor for minimal fuel consumption. On overrun, the intelligent energy management system automatically decides, in line with the driving situation and vehicle status, whether to recuperate braking energy or to coast with the powertrain disengaged.

At the same time, ECO PRO mode also programs electrical convenience functions such as the air conditioning, seat heating and heated mirrors to operate at minimum power consumption, but without compromising safety.

SPORT mode offers sequential manual gear selection and at the same time switches to very sporty drive and suspension settings. In SPORT mode, the engine and electric motor deliver extra-sharp performance, accelerator response is faster and the power boost from the electric motor is maximized. And to keep the battery topped up, SPORT mode also activates maximum energy recuperation during deceleration and braking. If the battery is being recharged using the car’s kinetic energy, the electric motor’s generator function switches to a more powerful setting. At the same time, gear change times are shortened and an extra-sporty setting is selected for the standard Dynamic Damper Control and the Electric Power Steering.

The BMW i8’s ECO PRO mode can also be used during all-electric operation. The vehicle is then powered solely by the electric motor. Only if the battery charge drops below a given level, or under sudden intense throttle application (kickdown), is the internal combustion engine automatically activated.

The dynamic chassis and suspension technology of the BMW i8 is based on a double-wishbone front axle and a five-link rear axle, the aluminum components and geometry of which are specially configured for intelligent weight savings.

The Electric Power Steering offers easy maneuvering in town and sports car-style high-speed steering precision, combined with particularly low energy consumption. Also standard is Dynamic Damper Control: the electronically operated dampers change their characteristics according to the selected driving mode to deliver the desired vehicle dynamics.

The DSC (Dynamic Stability Control) stability system includes the Anti-lock Braking System (ABS), Cornering Brake Control (CBC), Dynamic Brake Control (DBC), Brake Assist, Brake Standby, Start-Off Assistant, Fading Compensation and the Brake Drying function. The push button-activated Dynamic Traction Control (DTC) system raises the DSC thresholds, allowing some controlled drive wheel slippage for easier start-off on snow or loose ground, or for extra-dynamic cornering.

The chassis components of the BMW i8 are marked by their weight-minimized construction. The car’s standard 20-inch forged aluminum wheels have an aerodynamically optimized, lightweight design. CFRP wheels developed exclusively for the BMW i8 can be specified as an option in markets where regulations allow them. They allow a further reduction in weight in an area of the car which plays a particularly prominent role when it comes to agility. The use of three-piece wheels made from this extremely lightweight and high-strength material directly reduces unsprung masses and produces a weight saving of three kilograms per wheel.

Body and safety. The BMW i8 has its own version of the LifeDrive architecture developed for BMW i that gives it a unique range of tools for combining intelligent lightweight design and safety.

The horizontally split LifeDrive architecture consists of two separate, independent modules. The combustion engine and electric motor, battery pack, power electronics, chassis components, and structure and crash functions are arranged together in the aluminum Drive module, while the central element of the Life module is the 2+2-seater’s carbon-fiber-reinforced plastic (CFRP) passenger cell.

One of the stand-out characteristics of CFRP is its impressive torsional rigidity, with 50% less weight than steel and 30% less than aluminum. The LifeDrive architecture and high proportion of CFRP and aluminum in the car’s construction allow significant weight optimization.

The curb weight of the BMW i8 is 1,490 kilograms (3285 lb); the LifeDrive architecture also has a positive effect on how this weight is distributed. The battery unit is positioned low down in a central position, helping to give the car a low center of gravity and enhance safety accordingly. The center of gravity of the BMW i8 is less than 18 inches (460 millimeters) from the ground, making it lower than any other current BMW Group model. And this, like the car’s near perfect 50:50 weight distribution, ensures excellent handling properties.

The LifeDrive architecture also allows exceptional levels of freedom when it comes to body design. The structural strength of the CFRP passenger cell allows particularly large door apertures, which in turn ensure comfortable access to the rear seats of the BMW i8. The structure of the distinctive doors, which open forward and upwards like wings, is composed of a CFRP inner structure and an aluminum outer skin. This construction is 50% lighter than a conventional equivalent.

In its dry, resin-free state CFRP can be worked almost like a textile, and as such allows a high degree of flexibility in how it is shaped. The composite only gains its rigid, final form after the resin injected into the lattice has hardened. This makes it at least as durable as steel, but it is much more lightweight. The high tear resistance along the length of the fiber also allows CFRP components to be given a high-strength design by following their direction of loading.

To this end, the fibers are arranged within the component according to their load characteristics. By overlaying the fiber alignment, components can also be strengthened against load in several different directions. In this way, the components can be given a significantly more efficient and effective design than is possible with any other material that is equally durable in all directions—such as metal. This, in turn, allows further reductions in terms of both material use and weight, leading to another new wave of savings potential. The lower accelerated mass in the event of a crash means that energy-absorbing structures can be scaled back, cutting the weight of the vehicle.

The high-strength passenger compartment teams up with the intelligent distribution of forces within the LifeDrive module to provide the cornerstones for optimum occupant protection. Even after the structurally debilitating offset front crash with an impact speed of 64 km/h (40 mph), the extremely rigid material used for the passenger cell maintains an intact survival space for passengers. The crash-activated aluminum structures at the front and rear end of the Drive module provide additional safety.

Impressive rigidity, combined with its ability to absorb an enormous amount of energy, makes CFRP extremely damage-tolerant. Even at high impact speeds it displays barely any deformation. As in a Formula One cockpit, this exceptionally stiff material provides an extremely strong survival space. Less body deformation occurs compared with comparable steel bodies. Furthermore, the doors can be opened without any problem and the interior remains largely free of intrusions.

Rescue scenarios were worked through and checked as part of the development process. In standard cutting tests, the process of rescuing occupants from a BMW i8 involved in an accident was, in various scenarios, even more straightforward than that for conventional vehicles. That is because body components made from CFRP are lighter and can be more easily cut than high-strength steels, for example.

The safety characteristics of CFRP also come to the fore in side impact scenarios. Despite the heavy, in some cases concentrated forces, the material barely sustains a dent, and passengers enjoy unbeatable protection. This makes CFRP suited for use in a vehicle’s flanks, where every centimeter of undamaged interior is invaluable. If the forces applied go beyond the limits of the material’s strength, the composite of fiber breaks up into its individual components in a controlled process.

In the Euro NCAP side impact test, in which a pole strikes the side of the vehicle dead center at 32 km/h (20 mph), the Life module absorbs the entire impact with minimal deformation, ensuring optimum passenger protection.

The occupant protection concept is rounded off by standard safety equipment. Front airbags and side airbags integrated into the seat backrests, plus head/curtain airbags for both rows of seats, are all standard, as are three-point inertia-reel seatbelts including belt stoppers, belt tensioners and belt force limiters for all seats.

Crash-active aluminum structures in the front and rear sections of the vehicle also provide a level of safety for the Drive module. In a front or rear-end collision, these absorb a large proportion of the energy generated. The battery, meanwhile, is mounted centrally in the underbody section of the car to give it the best possible degree of protection. Statistically, this is the area that absorbs the least energy in the event of a crash, and the vehicle shows barely any deformation here as a result.

The high-voltage system is designed to cope with accidents beyond the legal requirements, with the high-voltage battery including features that ensure its safe reaction even in situations such as this.

The latest series of tests conducted by the DEKRA E-Mobility Competence Center were extensive—ranging from how a car might catch fire, how the flames might spread and what would be required to extinguish the fire, to the pollution caused by run-off of the water used for fighting the fire. The experts concluded that electric and hybrid cars with lithium-ion drive-system batteries are just as safe as vehicles with conventional drive systems. To ensure maximum safety in such a crash scenario, the high-voltage battery is disconnected from the high-voltage system and the connected components discharged when the passenger restraint systems are triggered.

Tests by vehicle insurers and BMW Accident Research show that accidents primarily result in minor damage. In around 90% of all recorded accidents involving conventional vehicles, the damage sustained is to the outer skin. The BMW i8 takes account of this and is equipped with thermoplastic body panels. If a section of the external skin needs to be replaced, this can be carried out quickly and economically. Overall, the accident repair costs are at a comparable level to those for conventional BMW models.

Repairs to the aluminum structure of the Drive module (welded as part of the series production process) are carried out using the “cold” methods of bonding and riveting. These methods have been in use successfully in BMW workshops since 2003.

The reparability of the Life module’s CFRP structure was already a priority in the development of the vehicle concept; for example, several repair stages were set out for the side frame. If a damaged side sill needs to be replaced after a side impact, the workshop carries out a visual inspection and damage assessment and then removes only the section in need of repair using a patented milling tool. The required side sill component is manufactured to fit and then installed on the damaged vehicle. The new part is bonded to the separation points using repair elements.

Any authorized BMW i dealer can repair the outer skin. However, due to the product-specific features of the LifeDrive module, there will be repair centers in which specialized employees take care of vehicles with damage to the aluminum or CFRP structure.

Laser headlights. The BMW i8 is the first series-produced vehicle to be available as an option with innovative laser headlights in markets where the regulations allow (they currently do not comply with US regulations). They generate a pure-white, extremely bright light that is pleasant to the eye. The light is created through the conversion of the beams emitted by tiny laser diodes by means of a fluorescent phosphor material inside the headlight.

Laser lighting is monochromatic—the light waves all have the same length. They also have a constant phase difference. As a result, laser lighting can produce a near-parallel beam with impressive luminance, which gives it an intensity a thousand times greater than that of conventional LEDs. The beam can also be adjusted extremely precisely. At the same time, the further optimized inherent efficiency of laser lighting means that laser headlights have less than half the energy consumption of even LED headlights, which are already very efficient. Laser lighting generates approximately 170 lumens (a photometric unit of light output) per watt, whereas LED lighting generates around 100 lumens per watt.

BMW ConnectedDrive and 360° ELECTRIC. The BMW i8 is equipped as standard with an integrated SIM card which provides the intelligent connectivity required to use the mobility services from BMW ConnectedDrive. It also introduces navigation services specially developed to enhance electric mobility—such as the Range Assistant with dynamic range map—alongside familiar features, including the Concierge Services information facility, the Intelligent Emergency Call function and the Online Entertainment music-on-demand service.

Drivers can use the BMW i Remote app to share information with their car at any time using their smartphone. For example, they can use their phone to control the charging process for the high-voltage battery and, while that is happening, also oversee the advance preparation of the vehicle before a journey.

The specially adapted version of the fully digital instrument display fitted in the BMW i8 shows the car’s speed and driving status information in a format and color selected to suit the driving mode currently engaged. SPORT mode brings traditional circular instruments for speed and rpm readouts. In COMFORT mode a “power meter” display replaces the rev counter to keep the driver up to speed on what the electric motor is up to, while ECO PRO mode adds an efficiency display, which encourages drivers to maximize fuel efficiency through their use of the accelerator.

The standard Navigation system links up with a version of the proactive drivetrain management system likewise specially developed for the BMW i8. When the route guidance function is activated, the drivetrain management is configured to ensure the electric motor is employed as extensively as possible and as wisely as possible from an efficiency point of view. The system analyses the route in full and sets up the drivetrain management, including energy recuperation strategy, to run on purely electric power over low-speed sections of the journey in particular. In so doing it ensures, for example, that the battery has sufficient capacity to cover the final stage of a longer journey through a built-up area in all-electric mode.

The performance characteristics of the electric motor and the capacity of the high-voltage battery have been set up to allow BMW i8 drivers to meet their urban mobility needs on electric power alone. Special displays in the instrument cluster keep the driver permanently informed of the remaining range (in kilometers) in all-electric driving mode.

The map display function of the Navigation system also contains a dynamic range display which uses a spidergram (range map) to show the area the car can cover on electric power alone. The map view also displays the location of public charging stations, allowing drivers to plan their journeys to incorporate a stop-off to charge the high-voltage battery. This means that additional battery capacity is then available for the remainder of the journey, which can either be used to continue the journey emission-free or to maximize the car’s dynamic performance by using the electric motor and combustion engine in tandem.

As well as the Navigation system, the standard specification for the BMW i8 also features a cruise control system with braking function; a rain sensor including automatic headlight activation; and Park Distance Control (PDC) with sensors at the front and rear of the car. The BMW ConnectedDrive driver assistance package available as an option comprises High Beam Assistant; a rear view camera; Surround View; Speed Limit Info including No Passing Info display; and Collision Warning with pedestrian recognition and braking function.

The BMW i8 also offers the driver the services of the BMW Head-Up Display which projects important driving data onto the windshield. Information including the car’s speed, status alerts from the driver assistance systems, Check Control messages, speed limits and overtaking restrictions can all be displayed in the driver’s direct field of vision.

The ConnectedDrive Services opens up an array of internet-based services to the driver. These include access to the BMW Online portal, the Online Entertainment features and the use of apps for further comfort and infotainment functions. The likewise optional Real Time Traffic Information system delivers precise traffic congestion warnings and detour recommendations in real time.

Its 360° ELECTRIC initiative also sees BMW i backing the use of electricity from renewable sources, and the brand has joined forces with selected partners to offer a choice of green power solutions in all markets. A strategic alliance between BMW AG and German eco power supplier naturstrom AG will in future give customers in Germany the opportunity to obtain an eco power package for running their BMW i vehicle. The company supplies electricity entirely from renewable sources, with a very high proportion coming from wind power.

Due to collaboration with car park operators and public charging station providers, BMW i also grants customers highly reliable access to the public charging infrastructure. BMW i assists the link-up between the vehicle, the driver and the outside world, providing users with features such as the display of available charging stations in the navigation system and on the customer’s smartphone, as well as a simple and transparent payment method with the ChargeNow card. This card enables access to charging stations operated by various providers and offers a cashless means of payment.