|BMW i3 Concept|
The BMW Group showcased its visions of future mobility in the shape of the BMW i3 Concept and BMW i8 Concept studies. Unveiled for the first time, these concept vehicles provide a glimpse of the first electrically powered production cars from the new BMW i sub-brand, due to be launched as the BMW i3 in 2013 and the BMW i8 in 2014.
BMW i stands for a new concept in sustainable mobility and a new approach to vehicle drive system design. The BMW i3 Concept and the BMW i8 Concept, with their highly innovative and efficient drive systems, demonstrate how future mobility can be both sustainable and dynamic. The BMW i3 Concept and BMW i8 Concept are two entirely different vehicles, and this is reflected in their different drive concepts. In both cases the design and configuration of the drive systems are dictated by the individual character of the vehicle and its intended area of application. While the BMW i3 Concept is an all-electric vehicle and therefore optimally equipped for operation around town, the plug-in hybrid BMW i8 Concept combines its electric motor with an internal combustion engine to deliver a high level of performance. The common link between the two vehicles is their electric motor, which marks a move away from exclusive reliance on an internal combustion engine. These cars are "born electric", and define a whole new concept in drive technology in their segment.
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 optimisation in terms of weight and driveability. It develops 125 kW/170 hp, with peak torque of 250 Nm (184 lb-ft). Typically of an electric motor, maximum torque is developed from standstill, in contrast to an internal combustion engine where torque increases with engine rpm. This makes the BMW i3 Concept highly agile and provides impressive acceleration. The BMW i3 Concept accomplishes 0-60 km/h (37 mph) in under four seconds and 0-100 km/h (62 mph) in under eight seconds.
At the same time the abundant torque is delivered over a very large rpm range, resulting in very smooth power delivery. The single-speed gearbox provides optimal power transmission to the rear wheels and accelerates the BMW i3 Concept to an electronically governed 150 km/h (93 mph) without the loss of power typically associated with having to shift gears. The speed governor cuts in at this point in the interests of efficiency: going even faster would result in very high energy consumption, which would unnecessarily restrict the driving range. The motor is located directly above the drive axle, for optimal and typical BMW rear-wheel-drive handling characteristics.
But impressive, instantaneous, response is not the only distinctive aspect about the driving experience in the BMW i3 Concept. Another is the dual accelerator/decelerator function of the accelerator pedal. After the driver eases up on the accelerator, the electric motor acts as a generator, converting the kinetic energy into electricity which is then fed back into the battery. Energy recuperation generates a braking effect which makes a significant contribution to vehicle deceleration. Around town, approximately 75 per cent of all braking operations can be performed in this way, i.e. without using the brake pedal at all. 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 unique "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 very user-friendly way of increasing the driving range even further.
The electric motor of the BMW i3 Concept not only offers attractive driveability, it also has a very high power-to-size ratio. This is partly explained by the fact that electric motors typically achieve over 90 per cent energy efficiency. This means that a smaller electric motor can produce the same power output as a larger internal combustion engine. Due to its compact size, the electric motor used in the BMW i3 Concept can be optimally integrated into the vehicle architecture. The permanently excited hybrid synchronous electric motor and the power electronics of the BMW i3 Concept were developed entirely in-house, and boast very high efficiency, optimised power delivery and compact design. As mentioned, the innovative nature of the electric motor is particularly evident in the favourable power-to-size ratio. As a result of continuous development and refinement, the space requirements of the electric motor used in the BMW i3 Concept have been reduced by 40 per cent 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 power needed to drive the vehicle and to operate all other vehicle functions is supplied by specially developed lithium-ion battery cells. The BMW i3 Concept's battery system has undergone detailed optimisation which significantly 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, which helps to significantly 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 degrees Celsius. These precautions ensure that power and torque remain constant throughout most of the battery's charge range and make the system significantly less sensitive to extreme external temperatures. The battery can be fully recharged in six hours at a standard power socket. If a high-speed charger is used, an 80 per cent charge can be achieved in just one hour.
As the MINI E field tests showed, a driving range of 120 to 150 kilometres (74 to 93 miles) was sufficient to meet 90 per cent of the mobility requirements of the pilot users. However, some customers want a longer driving range, or want their vehicle to be as flexible as possible. The BMW i3 Concept therefore offers an optional Range Extender, the REx, which allows the electric driving range to be increased. REx, a small, very smooth-running and quiet petrol 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 his destination. In a sense, therefore, the Range Extender is like having a reserve fuel can on board.
The very 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 petrol engine complies with the SULEV standard, currently the strictest emissions standard for internal combustion engines. To reduce fuel consumption to a minimum, REx also features such functions as Automatic Start-Stop and other intelligent operating strategies.
Company press release, last updated on July 31, 2011
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