Transport consumes almost 50% of oil production worldwide and is responsible for a large proportion of pollution emissions. In urban areas, noise generated by transport is the most common nuisance cited by citizens. The concentration of nearly 80% of the population in urban areas makes research into clean transport modes essential.
Since several years, major research efforts have been directed at developing electric-powered transport for short urban trips, and France is a leader in this domain with a range of electric vehicles adapted for urban passenger and goods transport. The context of the TAXEL project is therefore to extend the concept of electric traction in towns beyond passenger cars, delivery vehicles, buses, trams, etc, and develop an electric taxi.
TAXEL constitutes a research theme on an electric taxi for the final dissertation projects of students of five French engineering schools: ESTACA, Strate Collège, ESIEE, EIGSI and EIVL, from 1998 to 2000. At the initiative of ESTACA (Ecole Supérieure des Techniques Aéronautiques et de Construction Automobile), following the TAXIA project (innovative LPG-powered taxi), it has been supported by EDF (Electricité de France) and Taxis G7 (a major taxi operator in Paris).
This project was a 'desk study' in co-operation with 5 engineering schools and with sources from the industrial sector. In order to avoid the results of TAXIA disappearing as those responsible graduate from the school, the DRAST (research and scientific affairs directorate of the French Ministry of Transport) requested those responsible to create a synthesis, bringing together existing documentation and filtering the principal results, highlighting the most promising avenues of development and also manifest impossibilities.
These works were oriented to respond to needs expressed by taxi drivers, in order to allow them to benefit from an innovative, purpose-built taxi vehicle.
The project first required a literature study and interviews with taxi drivers in order to determine the needs, and thus the framework terms of reference for the vehicle. Then design solutions were proposed and tested.
The terms of reference for the TAXEL were inspired from the TAXIA project, completed by students, on the subject of an LPG-powered taxi. The experience gained in the design of this vehicle was a valuable benefit. The work carried out on TAXEL took on the main themes of TAXIA, adapting and improving specific points which were not adapted for electric vehicles.
In terms of the project organisation, each engineering school in the TAXEL partnership has been given a specific task, as follows:
- EIVL: in charge of the structure;
- ESTACA: in charge of architecture and dynamics of the vehicle;
- ESIEE: in charge of electronics and comfort;
- Strate Collège: in charge of design and interior fittings;
- EIGSI: responsible for the drive mechanism (propulsion).
The TAXEL project produced a comprehensive user needs analysis and field research measured from real taxi operations in Paris (literature analysis and interviews with 40 taxi drivers). These resulted in drawing up the basic terms of reference for the vehicle. These included the following:
- ability to carry up to 3 passengers (2 seats + 1 folding seat), as well as the driver;
- maximum unladen weight: 1700kg, maximum fully laden weight: 2200kg;
- weight of batteries: 375kg (later increased to 400kg);
- can carry 100kg luggage (in a compartment to the right of the driver);
- road clearance height from chassis (fully laden): 150mm;
- maximum length: 4.4m;
- maximum body width (excluding wing mirrors): 1.8m;
- maximum height (fully laden): 1.82m;
- autonomous running for 200km;
- maximum speed: 110km/h;
- acceleration: 0-50km/h in 8 seconds;
- aluminium "bird cage" structure (innovative, light and resistant);
- 2 or 3 Li-Ion type battery packs and an AC motor; and
- maximum use of existing parts in order to reduce costs.
Results and evaluation of options covered the whole range of the vehicle engineering, including flexion/torsion of materials, battery type and location, propulsion, braking, chassis structure, crash resistance, electrics and interior features/comfort.
Some key findings were as follows:
- Placing of batteries: in order to spread the load as evenly as possible across the vehicle chassis, it was decided to propose 3 blocks of batteries: one at the rear, one in the floor to the right of the driver (below the luggage space) and one at the front of the vehicle, forward of the motor compartment. As an example, the batteries at the front would comprise 20 modules (2 rows of 10) with a 50mm space between each module to allow for cooling. Dimensions of the front battery block were 1260mm wide x 564mm long x 250mm high, with a total weight of 167kg.
- Structure and chassis: 2 options were tested: a 185kg structure and a 110kg one. Both satisfied the criteria for torsion resistance, however the heavier version offered no resistance in a crash. For the second (110kg) structure, crash test results were ambiguous.
- Braking: the choice was constrained by factors such as the requirement to have regenerative braking in order to recoup energy and thereby optimise vehicle autonomy, the requirement to meet roadworthiness standards and norms, the fact that comfort is the main criteria rather than road-holdin
Because of the unsuitability of existing vehicle structures, a wholly electric taxi is a longer-term proposition. In the short-term, two hybrid solutions are favoured:
- Electric vehicle with "autonomy extension", using a small 6 to 8 kW motor which can recharge the batteries. This solution exists now using the Renault Kangoo (since 2002) and can reach, according to the vehicle manufacturer, an autonomy of some 200km.
- Fuel cell vehicle: based on the same principle as the vehicle above, i.e. the fuel cell replaces the motor and recharges the batteries. Autonomy in this case is between 200 and 300km. This solution does not yet exist except in the form of a prototype built by PSA Peugeot-Citroën (the "TaxiPAC"), however this vehicle is at present only a research vehicle and industrial production is unlikely before the year 2010.
The study developed a concept for an electric taxi. Main features from the passenger's point of view are:<?xml:namespace prefix = o ns = 'urn:schemas-microsoft-com:office:office' /????????????>
· Type of vehicle: Vehicle will be an MPV-type ('monospace') vehicle of an ultra-light and spacious design, with separated driver and passenger compartments.