Our prototype-class vehicle
Skilži during the unveiling ceremony
Skilži is our brand new prototype-class vehicle, designed to travel the equivalent of 1500 km per liter of gasoline. The car is meant to be a experimental vehicle for nurturing new and untested technology, which later on can be applied in more realistic contexts. The SEM2010 will be the first official measurement of vehicle performance.
Skilži is pronounced something like “skilDJCHÍ” and means “icicle” in Sami. Skilži follows the same winter theme as Baldos but refers to the shape of the vehicle rather than the motion. The basic idea for the design was to make it like an extended drop of water – the shape with the least wind resistance of all. An extended and solidified drop of water equals an icicle.
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Characteristics
Type: Prototype vehicle
Model: Unique
Owner: Luleå University of Technology
Approximate cost: € 20,000 excl./€ 150,000 incl. work
Width: 650 mm
Length: 2800 mm
Height: 631 mm
Kerb weight excluding driver’s weight: 38 kg
Number of seats: 1 (small)
Top speed: 50 km/h
Acceleration: 0-50 km/h in 4 s
Fuel consumption: unknown
Carbon dioxide emissions: unknown
Tank volume: 0,1 l
Drive train: Mechanical
Fuel: Ethanol
ICE type: Fuji Imvac BF-25EI, four-stroke
ICE displacement: 25 cc
Maximum power: ICE 1 kW
Maximum torque: ICE 1 Nm
Transmission: NuVinci hub
Coach: Carbon fiber monocoque, divinycell sandwich
Tyres: Michelin 45/75 R16
Rims: 20″ BMX
Brakes: Front; drum brakes, Rear; rim brake
Wheel suspension: Own-label, rigid
Interior: Austere; hand gas, five-point seat belt, cellular display, advanced GPS system, battle override control
Crashworthiness: Poor
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Drive train
The drive train of the prototype class vehicle consists of five basic parts. First is the internal combustion engine which runs on ethanol. From the ICE the power goes through a centrifugal clutch and a belt drive to a NuVinci® bicycle hub. From the CVP the power transfers via a standard bike chain to the rear wheel. The standard bike chain allows for simple engine-wheel-ratio change. Finally, to regain some of the energy lost in the ICE a turbine powered by the exhaust fumes will also help power the vehicle.
Internal Combustion Engine (ICE)
The ICE is manufactured by Fuji Imvac and is a four stroke engine with a volume of 25 cc. It delivers 1.6 hp at 7500 RPM. These data is when running the standard engine on gasoline.
We will optimize the engine in different ways, for example; running it on ethanol, replace the standard carburettor with electronic injection and make the compression higher. The intake manifold will be sized according to calculations for using the pulses in the intake manifold to fill the cylinder with the air-ethanol-mixture. All optimizations have its focus on high efficiency to make use of as much energy as possible from every drop of ethanol.
Engine control unit (ECU)
The ECU for the engine is based upon an AT90CAN microcontroller from Atmel that running the Tiny Timber real-time kernel. The ECU has six inputs, speed, lambda, temperature, speed control and primary and secondary trigger. It also has five outputs, injector, lambda preheat, ignition and two arbitrary outputs for future improvements. The ECU sends information to the ignition module which has its own Atmel µC. Both the ECU and the ignition module are prepared for use with CAN-bus.
NuVinci Continuously variable planetary (CVP)
The NuVinci is a bicycle hub with an internal continuously variable planetary transmission made by Fallbrook Technologies Inc. The infinite number of gear ratios within the range of the NuVinci makes it possible to run the ICE at its optimal speed. Since the NuVinci is originally designed to be used in a bicycle it has been optimized for the driving conditions of the Skilži.
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Controls
To travel far the vehicle needs not only an efficient drive train. A safe and precise control system is also needed. The vehicle is controlled via two joysticks, one for steering and one for shifting. To provide the driver with the right information at the right time a cell phone based heads up display system will be used.
Brakes and Shifting
Skilži uses bicycle brakes, drum brakes within the hubs of the front wheels and rim brakes at the rear wheel. The bicycle brakes provide adequate brake force and are light weight and reliable. The front and rear brakes are separately controlled by two bicycle brake handles at the steering and shifting joysticks.
The shifting joystick controls the NuVinci CVP. By pulling or pushing the joystick the gear ratio of the NuVinci is changed.
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Chassis
What would a car be without its chassis and wheels? The chassis is a self supporting monocoque made in carbon fibre. Suspension is of the minimalistic type to keep it as light as possible. For the wheels the standard Michelin prototype tires are used on a wide BMX-type rim.
Side view of Skilži
Body
The two most important factors when it comes to the coach are aerodynamics and weight. After studying aerodynamics the ultimate shape turned out to be an elongated water drop with as small frontal area as possible. Also applying the water drop shape to the wheel houses makes the entire body have minimum air resistance.
To reduce weight but still be durable the main part of the body will be made in carbon fibre. The front will be made of a vacuum formed lexan piece to ensure good visibility for the driver.
Wheels
The vehicle will have two steered wheels in front and one powered wheel in the rear. To decrease the frontal area of the vehicle the front wheels will be inclined. A Camber angle of 5-10 degrees will be used. To have a wheel able to handle the forces acting on a wheel only supported on one side a Sturmey Archer hub made for recumbent tricycles will be used. This unit also features a built in drum brake. On the hub a wide and stable 20″ BMX rim will be mounted. The tires used will be the radial Michelin tyres supplied by Shell Eco Marathon. The rear wheel will have the same rim and tire as the front wheels, but with a standard rear cassette hub.
