|Visio.M EV. Click to enlarge.|
The academic and industry partners in the Visio.M consortium (earlier post) are showcasing their new lightweight urban electric vehicle at eCarTec in Munich. The 2.5-year project was funded under the priority program “Key Technologies for Electric Mobility - STROM” of the German Federal Ministry for Education and Research (BMBF) with a total budget of €10.8 million (US$13.7 million).
The Visio.M has a range of around 160 kilometers (99 miles) and can accommodate two people with luggage. With only a 15 kW motor, the vehicle reaches a maximum speed of 120 km/h (75 mph). The electric motor in Visio.M draws its power from a lithium-ion battery pack behind the seats, which consists of consumer cells and provides a capacity of 13.5 kWh.
The battery weighs approximately 85 kg (187 lbs) and can be recharged in only three to four hours on a 230 V connection. In its total cost of acquisition and operation of the vehicle should be cheaper than a comparable gasoline engine, the partners said. To achieve the relatively long range from the relatively small battery pack, the partners used weight reduction, low aerodynamic resistance, an efficient drivetrain, low rolling resistance tires and energy-saving air-conditioning.
|Visio.M. Click to enlarge.|
One key to Visio.M’s high energy efficiency is its light weight; without the battery, Visio.M weighs only 450 kg (992 lbs). The passenger compartment consists of carbon fiber-reinforced plastic, while aluminum is used in the front, rear and room frame. All windows are made of LEXAN resin, a polycarbonate (PC) material, and coating technologies from SABIC.
Low weight is essential for an electric vehicle because more weight requires more battery power for the same range and thus causes higher costs. More weight also means less dynamics for the same performance. We wanted a car that is affordable and fun while driving.—Prof. Markus Lienkamp, TUM Chair of Automotive Engineering
Use of SABIC’s LEXAN resin compared to conventional glass for the car’s windows reduces weight by more than 13 kilograms (29 lbs) and also extends the vehicle’s driving range by up to 2 km (1.2 miles) for a single battery charge. The superior insulating properties also reduce demands on the car’s heating and air conditioning (HVAC) system and make possible up to 15 additional kilometers (9.3 miles) in extended range.
A significant share of an EV’s energy consumption depends on its weight. A low vehicle weight allows for smaller and lighter battery designs, in addition to lighter designs of the electric motor, the chassis and other components. The weight savings that we were able to achieve across our EV concept, including the significant drop in weight from the windows with SABIC’s materials and development support, allowed us to significantly reduce the amount of energy required to move the car and meet the design intent of the vehicle.—Stefan Riederer, BMW Research & Technology
Body and safety. Visio.M’s passenger compartment is an innovative, multi-piece monocoque made of carbon fiber-reinforced plastic in combination with ultra lightweight sandwich materials and is characterized by a particularly high level of rigidity.
In addition, the engineers have developed a security concept that consistently incorporates forward-looking analysis of the traffic. Using radar and camera sensors to provide a 360-degree view of the immediate vehicle environment, it is possible to detect critical driving situations early. This information is used not only for driver assistance and warning; if the vehicle detects the collision is not avoidable, it activates built-in occupant protection systems before the actual crash.
Novel structure airbags are mounted on the bumper and in the doors. A fraction of a second before impact, a gas generator fills these pressure hoses which serve as additional absorbent members.
Adaptive pretensioner and force limiter systems reduce the forces acting on the occupants. When the system detects an unavoidable side impact, the occupant will be moved inwards with the help of the seat and so moved away from the immediate danger zone. The pre-acceleration of the occupant reduces the crash pulse forces and increases the effectiveness of side airbags. A possible collision between the driver and front passenger is prevented by a built-in airbag between them.
Aerodynamics. The 1.55 m wide and 1.31 m high two-seater features a low drag coefficient of 0.24. The small frontal area of1.69 square meters and low rolling resistance tires (115/70 R 16) in addition to the low weight contribute to reduced energy consumption.
Active “Torque Vectoring” Differential. Instead of the standard bevel gears used in differential transmissions, the engineers developed a spur gear differential in which additional torque can be applied from outside via a superimposed planetary gearbox. (Earlier post.) The engineers integrated a small electric electric torque vectoring machine in the transmission; the unit can generate a large yaw moment at any speed to achieve the desired road handling dynamics.
The torque vectoring function adjusts the recuperation torque for both wheels individually. This increases vehicle stability while at the same time allowing more energy to be recovered.
HMI and connected services. In contrast to conventional cars, in which the driver’s heel is defined as a fixed point for adjustment functions, Visio.M chose the driver’s eye. The positioning of the safety systems and the view of the traffic can be optimally fitted to the driver. The car seat must be variable only in height, but the pedals are adjustable.
Controls for radio, air conditioner or navigation unit areis accessed via a central touch display, which is also adjustable. The man-machine interaction is based solely on wiping gestures that can be performed on the entire display.
The system is based on an open software architecture that can be easily expanded to include additional elements. This range from cloud-based music to more computationally intensive applications such as current weather and traffic data-based energy-efficient route planning run on a central server. Multiple kinds of premium services are feasible.
Energy-saving air-conditioning. Particular attention was paid in Visio.M also to the design of air and heating. Wherever heat is generated it is recovered when needed for the heating of the car. The air conditioner as well as the seats features Peltier elements for thermo-electric warming and cooling.
In very cold weather, an ethanol bruner provides range-neutral heating is available. The unit with a thermal heating power of about 4.5 kW ensures the defrosting of the windshield. An intelligent control allows you the operator to set the optimal solution for an energy efficient and comfortable operation of the climate system.
Participants in the Visio.M research project were the automotive companies BMW AG (consortium leader) and Daimler AG; TUM; Autoliv BV & Co. KG; the German Federal Highway Research Institute (Bundesanstalt für Straßenwesen, BASt); Continental Automotive GmbH; Finepower GmbH; Hyve AG; IAV GmbH; InnoZ GmbH; Intermap Technologies GmbH; LIONSmart Ltd.; Amtek Tekfor Holding GmbH; Siemens AG; Texas Instruments Germany GmbH; and TÜV SÜD AG.