|Cutaway of the BMW i3. Click to enlarge.|
With the launch of the production BMW i3 battery-electric vehicle (also available with a range extender) looming, the BMW Group provided more details about the first series-produced model from its new i brand, offering customers electric mobility in a premium small car package. (Earlier post.)
Like the car’s novel architecture—based around the LifeDrive structure and its carbon-fiber-reinforced plastic (CFRP) passenger cell (earlier post)—the electric motor, power electronics and high-voltage lithium-ion battery were developed and manufactured independently by the BMW Group under its BMW eDrive program. Also playing their part are the driver assistance systems and mobility services from BMW ConnectedDrive and 360° ELECTRIC designed specifically for the BMW i3.
The i3 offers what BMW calls an optimum balance of weight, performance and range for urban mobility. The key elements here are the LifeDrive architecture and BMW eDrive technology. With a DIN curb weight of 1,195 kilograms (2,630 lbs), the car is lighter than most compact vehicles, yet offers significantly more space for up to four occupants (US specific weight specifications will be available closer to the US launch).
The use of lightweight CFRP for the passenger cell cancels out the extra weight contributed by the lithium-ion battery, while the low, central positioning of the battery pack enhances the car’s agility due to near-perfect 50:50 weight distribution.
|eDrive unit and battery pack. Click to enlarge.|
Motor. The hybrid synchronous electric motor developed and produced specially by the BMW Group for use in the BMW i3 generates output of 125 kW/170 hp with maximum torque of 250 N·m (184 lb-ft). The BMW i3 accelerates from 0 to 60 mph (about 0-100 km/h) in about seven seconds; 50 – 75 mph (80 to 120 km/h) takes 4.9 seconds.
Beyond the traditional immediacy of response offered by electric motors when pulling away, power development in the BMW i3 also remains unbroken through higher speeds. Power is sent to the rear wheels through a single-speed transmission, allowing the BMW i3 to accelerate with an uninterrupted flow of power up to its top speed, which is limited to 93 mph (150 km/h).
This linear power delivery extending into high rev ranges can be attributed to a special electric motor design developed exclusively for the BMW i3. A specific arrangement and dimensions for the components used to generate drive produces a self-magnetizing effect only otherwise induced by reluctance motors. This additional excitation causes the electromechanical field formed by the current supply to remain stable even at high revs. The maximum revs of the motor developed for the BMW i3 – known as a hybrid synchronous motor on account of its specific combination of properties – are 11,400 rpm.
The design principle behind the electric motor in the BMW i3 helps it to run extremely effectively across a wide load band. The motor’s average power consumption of around 0.13 kWh per kilometer (0.21 kWh per mile) in the New European Driving Cycle (NEDC) plays a key role in optimizing the car’s range.
Also helping to deliver the BMW i3’s driving experience is the single-pedal control feature. Recuperation mode is activated the moment the driver takes his foot off the accelerator. The electric motor switches from drive to generator mode, feeding power into the lithium-ion battery. At the same time, it generates a precisely controllable braking effect.
This recuperation is speed-sensitive, which means the car “coasts” with maximum efficiency at high speeds and generates a strong braking effect at low speeds. The ability to accelerate and brake using just one pedal creates a uniquely direct interaction between driver and car. Thinking ahead in city traffic can allow the driver to carry out 75% of braking maneuvers without applying the brake pedal, BMW says. The brake lights illuminate if the amount of recuperation in progress produces the same braking effect as actually pressing the brake pedal. The conventional braking system only joins the action if the driver summons greater braking power by depressing the brake pedal.
Intensive use of this form of brake energy recuperation through the motor also increases the range of the BMW i3 by as much as 20%. The “coasting” facility further enhances the user-friendly nature of single-pedal control. The BMW i3’s accelerator has a distinct “neutral” position; i.e. rather than switching straight to energy recuperation when the driver eases off the accelerator, the electric motor uses zero torque control to decouple from the drivetrain and deploy only the available kinetic energy for propulsion. In this mode, the BMW i3 glides along using virtually no energy at all.
Battery. The lithium-ion battery enables the BMW i3 to achieve a range of 80 – 100 miles (130 - 160 km) in everyday driving. This can be increased by up to approximately 12% in ECO PRO mode and by the same amount again in ECO PRO+ mode.
In addition to the battery, the BMW Group also developed numerous battery system components including specific components which ensure the interconnection of the cells themselves as well as the connection between the battery system and the vehicle. They also comprise the integrated control unit and the electronic components in the proximity of the cells, including battery management sensors.
Apart from procurement of storage cells from a specialist manufacturer, all the development and manufacturing stages are carried out at the BMW Group. The high-voltage battery is produced on a state-of-the-art assembly line at BMW Plant Dingolfing.
The battery pack n the BMW i3 consists of eight modules (each with 12 individual cells), which together produce a rated voltage of 360 volts and generate approximately 22 kWh of energy. In order to maintain cell output and storage capacity over time, the battery management system controls both the charging and the discharging processes, as well as the operating temperature of the cells.
When the vehicle is on the move all the cells are used equally to supply energy. However, it is also possible to replace individual modules in the event of a fault. The air conditioning coolant is used to provide cooling of the high-voltage battery, and this fluid can also be warmed using a heat exchanger. All these characteristics enable the optimum operating temperature of around 70 °F (20 °C) to be reached before a journey begins, even when the ambient temperature is low.
This preconditioning ensures the battery operates to optimum effect in terms of power output, range and durability. The BMW Group has planned and developed this battery to last for the full life of the vehicle.
The battery pack is mounted flat in the Drive module and weighs approximately 450 lbs (230 kg). The battery casing and its model-specific attachment systems were developed by the BMW Group to provide the high-voltage battery with extensive protection against environmental factors and in the event of a crash.
Three levels of safety, including a cut-off mechanism, for the car’s software and hardware provide protection for the electrical system as a whole.
Power electronics. The power electronics responsible for the interaction between the battery and electric motor are also developed by the BMW Group. The power electronics serve both as an inverter for the power supply from the battery to the electric motor and as a voltage transducer interacting between the high-voltage battery and the 12-volt onboard power system.
Software control ensures the best possible current flow during energy recuperation on the overrun.The operation of battery charging systems is also integrated into the power electronics, which regulate charge outputs of between 3 kW and 50 kW, depending on the electricity source.
Charging. Customers can charge their car from a home BMW i charging station. In the US, it can also be charged from any public charging station with a SAE J1772 connector. When the BMW i3 is plugged into a public DC fast-charging station (50 kW) it only takes about 20 minutes for the battery to reach 80% capacity.
Range extender. If desired, the BMW i3 is also available with a range-extender engine, which maintains the charge of the lithium-ion battery at a constant level while on the move as soon as it dips below a certain value.
The 650cc two-cylinder gasoline engine, which is mounted immediately adjacent to the electric motor above the rear axle, develops 34 hp/25 kW. Specifying the range extender has no effect on luggage capacity: the 2.4 gallon (nine liter) fuel tank is located in the front section of the car.
The combustion engine drives a generator to that produces electricity. It is brought into play as required, responding optimally to match the load and running extremely efficiently. Driving in ECO PRO mode or ECO PRO+ mode can increase the range of the BMW i3, in each case by up to approximately 12%. If the range extender is specified, the BMW i3 will be able to travel more than 60 miles (100 km) further before refueling. The BMW i3 is first currently produced battery-electric car to offer the option of a range extender engine used exclusively to generate electric power.
Ancillaries. As well as the drive unit, all the other electrically powered systems on board the BMW i3 are also designed to run as efficiently as possible. For example, energy-saving light diodes are used to provide interior and exterior illumination. And an optional interior heating system based on the principle of a heat pump uses up to 30% less energy in city driving than conventional electric heating.
The aim in determining the range of the BMW i3 was to ensure that customers could cover their typical energy needs by charging the car twice or three times per week. The studies carried out as part of project i—involving more than 1,000 participants and conducted over some 12.5 million miles (20 million km)—revealed that the average daily distance covered was around 30 miles (45 km). Customers can charge their cars using either the home charging station supplied by BMW i or any public charging station that uses a Level 2 SAE J1772 charging system.
Weight reduction. The LifeDrive architecture developed specifically for BMW i models has created an optimized framework for purpose-built electrically powered car concepts. Here, the carbon-fibre-reinforced plastic (CFRP) construction of the passenger cell (Life module) plays a central role. Such extensive use of this lightweight and crash-safe high-tech material is currently unique in volume car production.
The principle of lightweight design also governs the aluminum Drive module and the connection between the two elements. The body structure—shaped by its LifeDrive architecture—enables the use of a trailing edge element made by glass-fiber-reinforced plastic injection molding. And that contributes a 30% weight saving compared with a conventional sheet steel solution.
The direct connection between the power electronics and electric motor in the rear of the BMW i3 reduces the length of cabling required and cuts the overall weight of the drivetrain by around three pounds (1.5 kilograms).
Weight-minimizing construction also sets the tone for the chassis components of the BMW i3. For example, the forged aluminum suspension links weigh around 15% less than in a conventional design, the hollow drive shaft is 18% lighter than a conventional equivalent, and the standard 19-inch forged aluminum wheels of the BMW i3 are 36% lower in weight than comparable steel rims of the same size.
Using a magnesium supporting structure for the instrument panel saves weight on two fronts. Superior material attributes over conventional sheet steel allow these components to boast optimized geometry, which results in a weight reduction of some 20%. In addition, the high composite rigidity of the magnesium supporting structure lends it a strengthening effect, which allows a reduction in components and lowers weight by a further 10%.
The door trim panels are made from renewable raw materials and tip the scales around 10% lighter than conventional equivalents. The detailed commitment to the principle of lightweight design is lent visible expression by the honeycomb structure of the windscreen wiper blades. In addition, a cast aluminum mount was developed specially for the wipers of the BMW i3, its force-flow-optimized geometry also yielding a reduction in weight.
The battery is encased in aluminum sections and is well positioned from a crash safety perspective. The electric motor and transmission unit are located in direct proximity to the driven rear axle. Underpinning their space-saving integration into the Drive module is a compact construction facilitated by the in-house development of the drive components at the BMW Group.
Steering and ride. The subdivision of Life and Drive modules means no central tunnel is necessary. The car’s rear-wheel drive allows the front axle to remain free of torque steer and fulfill its steering function to full effect. As with current models from the BMW and MINI brands, the i3 uses electric power assistance.
The BMW i3 has MacPherson single-joint front suspension and a five-link rear axle mounted directly to the Drive module. This design assists the functional separation of wheel location and suspension, resulting in sporting driving characteristics defined by longitudinal and lateral dynamics combined with suspension comfort. The adherence to lightweight design principles yields a reduction in unsprung masses to the benefit of ride comfort at all speeds. The BMW i3’s forged aluminum wheels also offer outstanding rigidity and low weight.
The standard DSC (Dynamic Stability Control) system offers all the functions familiar from current BMW models, including 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 DTC (Dynamic Traction Control) mode, activated at the touch of a button, raises the intervention thresholds of the stability control system and allows a controlled degree of slip through the BMW i3’s driven wheels when pulling away on snow or loose sand or in particularly dynamic cornering.
ConnectedDrive. An embedded SIM card in the BMW i3 is the key that unlocks BMW ConnectedDrive services available to the new electric model. For example, it introduces navigation services specially developed to enhance electric mobility alongside familiar features including the Concierge Services information facility and the intelligent BMW Assist eCall.
Drivers can use the BMW i Remote app to share information with their car at any time using their smartphone. The pedestrian navigation function guides the driver from parking place to final destination and back, while BMW ConnectedDrive also offers intermodal route guidance, incorporating local public transport connections into journey planning.
BMW ConnectedDrive services specifically designed for BMW i focus on the areas of navigation and energy management. Range Assistant is engaged both for route planning and during journeys already under way. If the destination programmed into the navigation system is beyond the car’s range, the system suggests switching to ECO PRO or ECO PRO+ mode and calculates a more efficient route. If the driver needs to charge the battery at a public charging station, a list of available stations in the area is displayed.
The navigation system of the BMW i3 also comes with a dynamic range display, which supplies drivers with information on whether there is sufficient charge to reach their destination and, if so, how much power will remain at the end of the journey. Many factors affecting range are considered in the calculation process, which is carried out on a BMW server and sent to the navigation system via the SIM card installed in the car. The range readout is presented in the form of a spider map on the navigation system in the central information display.
The BMW ConnectedDrive Remote app for BMW i enables smartphone access to useful vehicle data for journey planning. If the BMW i3 is connected to a charging station, the supply of energy can be controlled via smartphone, while the air conditioning and heating function for the high-voltage battery pack can also be activated remotely. In addition, customers can use their smartphone to send destinations to their car’s navigation system.
The app also shows the driver charging stations (both available and in use) and can establish if the car has sufficient power remaining to reach them. The car’s range limit display on the smartphone screen replicates that provided by the car’s navigation system.
The BMW i3 is also available with an array of other BMW ConnectedDrive driver assistance systems developed specifically to enhance convenience and safety in urban conditions. These include Driving Assistant Plus, Parking Assistant, a rear view camera and Speed Limit Info.
The Driving Assistant Plus that is optionally available for the BMW i3 comprises Collision Warning with brake priming function, which is activated at speeds up to about 35 mph (60 km/h) and is able to respond to both moving and stationary vehicles ahead, as well as to pedestrians. It also comes with Active Cruise Control including Stop & Go function.
In addition to visual and audible warnings, the system is furthermore capable of braking the vehicle by itself, if required, with up to maximum stopping power.
The Parking Assistant performs the steering maneuvers at the same time as controlling accelerator, brake and gear selection, enabling fully automated parallel parking of the BMW i3. There is also the option of a rear view camera for the BMW i3 to supplement the standard Park Distance Control (PDC) with rear sensors. Another optional extra is the Traffic Jam Assistant that allows drivers to delegate the tasks of pulling away, braking and steering to keep the vehicle in lane. Meanwhile, the Speed Limit Info system is also offered in conjunction with the navigation system.
360° ELECTRIC package. BMW i offers a range of products and services in its 360° ELECTRIC package to meet individual customer needs for energy supply and journey planning. The spectrum of services ranges from the installation of the BMW i Wallbox in the customer’s garage and special renewable energy supply offers, to the charging card for user-friendly access to the public charging infrastructure and additional assistance services from BMW ConnectedDrive.
If the BMW i3 concept fails to meet mobility requirements in a specific situation, 360° ELECTRIC provides flexible mobility solutions including alternative vehicles from BMW.
Assistance services. To make sure the BMW i3 runs smoothly during everyday operation, the battery and remaining electrical systems are monitored even while the vehicle is being driven. In the case of a malfunction, BMW i Centers are able to carry out vehicle diagnostics to pinpoint any faulty components so that the BMW i3 is ready to be driven again in the shortest time possible.