CLEVER: A Three-Wheeled, Natural Gas, Two-Seat Urban Vehicle
2 December 2005
A European research consortium is wrapping up a three-year project to develop a three-wheeled, natural-gas powered micro-car: CLEVER (Compact Low Emission VEhicle for URban Transport).
CLEVER, a €3.3 million (US$3.9 million) effort, is an enclosed two-seater that combines the safety of a microcar, and the maneuverability of a motorcycle, while being less polluting than other vehicles as it runs on compressed natural gas.
Its strengthened frame will protect the driver in a crash and the vehicle will have a top speed of approximately 50 mph.
The 230cc BMW engine—modified by Institut Français du Pétrole (IFP) to use natural gas—produces 12.5 kW (17 hp) of power and maximum torque of 15.5 Nm at 6,300 rpm.
IFP increased the swept volume of the engine cylinders, allowing the engine to run more slowly and bringing several benefits. The lower engine speed both reduces emissions and lowers engine friction, which enhances fuel efficiency. It also produces less noise. The increased displacement contributes to the higher torque, providing the level of acceleration needed in urban traffic.
Fuel consumption is estimated to be 2.4 liters/100 km gasoline equivalent (98 mpg US), with 59.5 g/km of CO2 emissions.
|The fuel tank system.|
The compressed natural gas is stored in two removable cylinders that are custom designed for ease of handling and refilling. The two connected gas bottles provide a range of approximately 150 km (93 miles).
A problem with three-wheel vehicles with a symmetrical wheel layout is the tipping moment when cornering, which cannot be controlled at high speeds if the vehicle has a short wheelbase.
To solve this problem the vehicle’s center of gravity can be moved towards the center of the corner, for example by angling the complete vehicle—just as a motorcycle does when it corners.
This is the approach used by “tilting three-wheelers”—and there have been two basic technical methods to achieve it:
Change the camber of the two parallel wheels (front or rear) with or without tilting the vehicle.
Angle the vehicle around a pivot relative to the axis of the two parallel wheels.
Vehicles that use the first concept have been around since the forties (Ernst Neumann-Neander 1948) and the method has regularly been used for concept cars (Mercedes Benz F300 “Life Jet” 1997).
Vehicles that use the second concept include, for example, the “GM Lean Machine” dating from 1983, the “Carver” from Vandenbrink and various scooter-type vehicles from Honda, including the Honda Gyro/Honda Stream dating from 1984. There has been a BMW concept on this basis in the BMW Museum in Munich since 1991.
|The cabin-tilting CLEVER. The rear section, with the engine, remains upright, while the cabin tilts.|
The CLEVER vehicle is a cabin tilter, with the system designed by the University of Bath. The cabin with the front wheel is connected to the power unit and the two rear wheels by a pivot bolt. The rotary movement of the cabin is produced by two hydraulic cylinders (actuators) that are installed between the cabin and the power unit. The actuators create the rotary angle of the cabin of +/-45° relative to the vertical power unit.
The hydraulic system consists of a pump that is driven direct by the engine and a pressure accumulator that maintains the oil pump if the pump suffers a defect. The two single-action hydraulic cylinders are controlled by an electromagnetically actuated valve.
The signals for the hydraulic control valve come from a freely programmable computer that processes the input signals from a sensor system, such as speed, tilt angle of the cabin and lateral acceleration.
CLEVER was funded by the European Commission with the Growth Programme of the Fifth Framework Programme. Partners included:
- Technical University of Berlin, Institute for Land and Sea Transport (TUB), Berlin, Germany
- Cooper-Avon Tyres Ltd, Melksham, Great Britain
- ARC Leichtmetall Kompetenzzentrum Ranshofen GmbH (LKR), Ranshofen, Austria
- TAKATA-PETRI AG, Berlin, Germany
- University of Bath, Department of Mechanical Engineering, Institute for Power Transmission and Motion Control, Bath, Great Britain
- Universität für Bodenkultur Vienna, Institute of Transport, Vienna, Austria
- WEH GmbH, Illertissen, Germany
(A hat-tip to Wolf Faust!)
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