|The i8 (left) and i3 Concepts. Click to enlarge.|
BMW unveiled the i3 and i8 Concepts in Frankfurt, providing a look at first electrically powered production cars from the new BMW i sub-brand, due to be launched as the BMW i3 in 2013 and the i8 in 2014. (Earlier post.)
The rear-wheel drive battery-electric (BEV) i3 Concept has been specifically developed for use in an urban environment and features a 125 kW electric motor with torque of 250 N·m (184 lb-ft) and a range of approximately 150 kilometers (93 miles). (An optional gasoline-powered range extender can provide further range.) With its LifeDrive architecture (earlier post) featuring a carbon passenger cell, the BMW i3 Concept combines an extremely low weight of 1,250 kilograms with optimal interior space and the highest crash safety levels. The 4-seat i3 Concept has a 200-liter (7 ft3) luggage compartment.
|LifeDrive Architecture for the i3. Click to enlarge.|
With a value-added chain designed to be sustainable all along the line, life cycle emission figures for the BMW i3 are at least a third lower than for a highly efficient combustion-engine car, BMW says. If the BMW i3 is run on electricity from renewable sources, the figures improve by well over 50%.
The i8 Concept features a plug-in hybrid (PHEV) drive with a system output of 260 kW and a range of up to 35 km (22 miles)in all-electric mode. For more dynamic driving or out-of-town routes, a high-performance 1.5L, three-cylinder gasoline engine comes into play. The BMW i8 Concept goes from 0 to 100 km/h in less than five seconds and boasts fuel consumption of under three litres per 100 km (78 mpg US). The sports car has an electronically governed top speed of 250 km/h (155 mph) and space for up to four occupants.
We are marking another milestone in the history of the BMW Group. As Chairman of the Board and an engineer myself, I am very proud of this project. As the world’s leading premium car manufacturer, our aim is to offer customers purpose-built electric-drive cars as well.—Norbert Reithofer, Chairman of the Board of Management of BMW AG
i3 Concept. The electric motor of the BMW i3 Concept is designed primarily for operation in an urban environment. Already tested in a pre-production version in the BMW ActiveE, the version of this permanently excited hybrid synchronous motor which will be used in the BMW i3 Concept has undergone further optimization in terms of weight and driveability.
A single-speed gearbox accelerates the BMW i3 Concept to an electronically governed 150 km/h (93 mph). The BMW i3 Concept accomplishes 0-60 km/h (37 mph) in less than four seconds and 0-100 km/h (62 mph) in under eight seconds. The motor is located directly above the drive axle, for optimal and typical BMW rear-wheel-drive handling characteristics.
With the dual accelerator/decelerator function of the accelerator pedal approximately 75% of all braking operations around town can be performed by energy recuperation which generates a braking effect, BMW says. Intensive use of this energy recuperation function of the electric motor can increase the driving range by up to 20 per cent. Only when the driver’s braking request exceeds a given level is the conventional brake system of the BMW i3 Concept engaged as well.
A coasting facility makes this single-pedal control of acceleration and braking using just the accelerator even more user-friendly. The BMW i3 Concept features a distinct “neutral” position of the accelerator pedal—i.e. rather than switching straight to recuperation when the driver eases off the pedal, the electric motor’s zero torque control keeps the drive train disconnected as long as the pedal is in this position. The vehicle now coasts without consuming power, driven by its own kinetic energy. Used as part of a proactive driving style, this coasting mode is a way to increase the driving range even further.
BMW developed the motor and power electronics for the i3 Concept entirely in-house. The space requirements of the electric motor used in the BMW i3 Concept have been reduced by 40% compared with the motor used in the MINI E. This compact drive unit is mounted over the rear axle, together with the power electronics, transmission and differential, causing no loss of interior space.
The BMW i3 Concept’s battery system has also undergone detailed optimization which reduces the extent to which external factors can influence the vehicle’s power and driving range. An integrated liquid cooling system keeps the battery at its optimal operating temperature at all times, helping to boost the performance and life expectancy of the cells. The climate/heating system cools the fluid circulating in the battery housing via a heat exchanger.
If necessary, in winter, this fluid can also be heated in order to bring the battery up to its optimal operating temperature of around 20 °C. The battery can be fully recharged in six hours at a standard power socket. If a high-speed charger is used, an 80% charge can be achieved in just one hour.
Optional range extender. The BMW i3 Concept offers an optional Range Extender, the REx, which allows the electric driving range to be increased. REx, a small gasoline engine, drives a generator which maintains the battery charge level and therefore extends the range of the electric motor. As soon as the battery charge reaches a critical level, REx supplies the necessary energy to get the driver the rest of the way to the destination.
The compact size of the electric motor used in the BMW i3 Concept means there is room left over to accommodate REx and its attached generator over the rear axle, alongside the drive components. The gasoline engine complies with the SULEV standard. To reduce fuel consumption to a minimum, REx also features such functions as Automatic Start-Stop and other intelligent operating strategies.
i8 Concept. The electric motor in the i8 Concept has been adopted from the BMW i3 Concept and modified for use in the i8 Concept’s plug-in hybrid power train—i.e., for operation with a smaller battery pack and in conjunction with an internal combustion engine. It drives the front axle, while a 164 kW/220 hp turbocharged three-cylinder gasoline engine developing up to 300 N·m (221 lb-ft) of torque drives the rear axle. Together, the two drive units take the vehicle to a governed top speed of 250 km/h (155 mph).
Like the electric motor, the 1.5-liter three-cylinder gasoline engine was developed entirely in-house by the BMW Group.
A high-voltage generator attached to the internal combustion engine can generate power for recharging the batteries. This option is only used to increase the range of the vehicle while out on the road, and is not intended as a substitute for stationary recharging at an electric power socket.
Locating the electric motor at the front axle of the BMW i8 Concept optimizes braking energy recuperation, since the front axle is where greater braking forces are developed due to the dynamic wheel load shift when decelerating. Whenever there is a chance to recuperate braking energy, intelligent driving dynamics systems make the most of it, taking into account traction conditions and driving situation, without compromising stability and dynamics, BMW says. This allows very high levels of braking energy recuperation even in the wet or in snow. Depending on requirements, braking is initially provided by the recuperation function and only when more powerful braking is required is the conventional brake system engaged.