The Trev project started at the University of South Australia in about 2004. The aim was to design, build and demonstrate a low-mass, energy-efficient vehicle designed specifically for commuting.
The following requirements were compiled:
- two comfortable seats, luggage space, easy entry & exit, and good all round vision
- a small, aerodynamic body
- mass, without occupants, less than 350 kg (prototype was about 300 kg)
- energy-efficient tyres, brakes and suspension
- an efficient electric drive system
- performance at least as good as conventional cars
- compliance with road safety and worthiness regulations
- cost comparable to that of small conventional cars
- commuting range of 100-150 km
- electrical energy use less than 200 kJ/km (60 Wh/km).
We chose a 2+1 layout for several reasons:
- three wheels is something between a motorcycle and a car
- we could make the vehicle narrow at the back, for improved aerodynamics
- lower mass (one less wheel and associated suspension)
- simpler suspension
- minimal torsional loads on the chassis.
In Australia, three-wheeled vehicles must meet stability requirements defined in Australian Design Rule ADR 42: the height of the centre of mass must not exceed 1.5 times the distance to the nearest roll axis (between a front wheel and the rear wheel). The Team Trev version of Trev, with two occupants, had a load of 1410 N on each of the front wheels and 2080 N on the rear wheel, which placed the centre of mass 0.98 m behind the front axle and 0.32 m from the nearest roll axis. The height of the centre of mass had to be less than 0.48 m, which was easily achieved.
The tandem seating arrangement kept the car narrow, and allowed good aerodynamics.
The composite tub chassis was easy to build and had low mass---about 32 kg.
An electric drive system is compact and simple, and can be powered using renewable energy. The power required is about 5 kW continuous and 20 kW peak. Trev has an air-cooled motor and controller.
Trev was designed so that it could be built by university students. The construction techniques are simple, and do not require a lot of specialised tools. However, building an electric car does require many type of expertise: design, mechanical, electrical, electronic and software.
No photovoltaic panels
Trev does not have photovoltaic panels on the vehicle. Photovoltaic panels are much more effective on the roof of a building, where they can be pointed towards the path of the sun, and are always outside.
A 1 m2 photovoltaic panel on Trev might generate 1000 Wh of energy on a sunny day—enough to drive about 15 km. (Solar racing cars are much lighter, have much lower aerodynamic drag, and have 6 m2 of very expensive photovoltaic cells.)
A small PV array could be used to power ventilation fans when the car is parked in the sun.
In the 2007 World Solar Challenge, the UniSA Trev was driven 3000 km from Darwin to Adelaide. It cruised at 80-90km/h, traveling an average of 431 km per day with an average energy consumption of 6.2 kWh/100km. This energy use was at high cruising speeds. Similar or lower energy use is likely for urban commuting.
Under highway conditions, the prototype Trev achieved a range of 120 km. A motor that is more efficient at light loads would give an even greater range.
In 2010-2011, Team Trev drove a modified version of Trev around the world. This version had a 13 kWh battery, which gave it a range of up to 250 km.
The main improvements required are:
- isolation of motor and road noise from the tub chassis—Trev is noisy when you are inside it
- lower the rear seat to the same height as the front seat, to give more shoulder room in the back
- a windscreen cleaning system that does not scratch the acrylic canopy
- improve the suspension to reduce body roll (the Zero Race suspension is probably too soft for good roads)
- more usable and more accessible luggage space.
Team Trev has documented the lessons learnt.