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Gordon Murray T.27 unveiled; Zytek provides more details on 25 kW EV powertrain
29 June 2011
|The T.27. Click to enlarge.|
At an event held at the Royal Automobile Club, Pall Mall, London Gordon Murray Design unveiled its latest ultra-compact electric city vehicle, the T.27 (earlier post), along with the updated specification and performance targets for the car.
In parallel with the announcement of the completion of the Gordon Murray Design T.27 electric vehicle program, Zytek released more details regarding the electric drivetrain developed for use in this lightweight vehicle.
T.27 The design and development program for the T.27 was a £9-million (US$14.4 million) project, made possible through a £4.5-million (US$7.2-million) investment from the government-backed Technology Strategy Board. The program took only 17 months, including the design and build of a completely new electric powertrain by Zytek Automotive Ltd, one of the consortium partners.
|Specs for the T.27. The car will make its public road debut at the RAC Future Car Challenge on 5 November 2011. Click to enlarge.|
T.27 specifically targets the urban city environment via a novel manufacturing process (iStream, earlier post) developed by consortium lead partner Gordon Murray Design, it aims to significantly reduce lifecycle impacts and enable low cost, efficient manufacture within the UK. The partners say the electric car sets new standards in weight, footprint, small car dynamics, safety, packaging and efficiency whilst addressing full lifecycle CO2 emissions, congestion, parking and low-cost motoring.
The lightweight iFrame geometry in the T.27 allowed every aspect of the vehicle to be optimized including Zytek Automotive’s integrated powertrain.
Gordon Murray Design recently achieved first class results in a second crash test on the vehicle—the EuroNCAP 50 km/h mobile deformable barrier (MDB) protocol, confirming the structural integrity of an iStream manufactured chassis during a side impact.
The T.27 features lower energy consumption per mile that other EVs: the Smart EV uses 29% more energy per km, the Mitsubishi iMiEV uses 36% more energy per km, and the Mini-E uses 86% more energy per km, according to the partners.
I must congratulate Gordon Murray Design and their partners for developing the T.27 prototype – and in rapid time. The growing pressure for more environmentally friendly transport, from both customers and regulators, is creating new business opportunities in the fast-developing market for low carbon vehicles. The Technology Strategy Board exists to help drive dynamic technological innovations such as the T.27, which are key to meeting our climate change goals.—Iain Gray, Chief Executive of the Technology Strategy Board
Gordon Murray Design is currently talking to three possible manufacturers for T.27. The car will make its public road debut at the RAC Future Car Challenge on 5 November 2011.
Zytek 25 kW powertrain and battery pack. Partially supported by a £1.5-million (US$2.4-million) investment by the UK Technology Strategy Board, Zytek’s goal was to develop a highly compact, power-dense drivetrain available for use in lightweight, low-cost electric vehicles. Zytek was responsible for all aspects of the design and manufacture of the complete drive system, including motor, inverter, battery, in addition to working very closely with the gearbox supplier Vocis.
Minimizing the torque requirement of the motor (to allow it to be smaller, lighter and more efficient) while maintaining vehicle performance, requires a high motor speed. Zytek analyzed a wide variety of motor topologies and designs using 2D and 3D simulation tools, leading to a reliable maximum motor speed of 14,500 rpm. This high operating speed allowed motor torque to be reduced to 64 N·m (47 lb-ft) while maintaining vehicle based performance targets.
The peak motor power of 25 kW (available for 30 seconds) means vehicle performance is maintained in all expected usage conditions.
The second major powertrain component is the three-phase inverter. Zytek concluded that the inverter should also combine battery charging and high-voltage switching capabilities. This has the added benefit of reducing the weight of high-current copper cable and also avoiding any reliability issues associated with use of high voltage connectors.
Zytek produced the first working prototype systems after six months. This design underwent a highly accelerated dyno-based development and durability exercise, feeding into a second stage design which has been installed on the launch version of the Gordon Murray Design T.27 electric vehicle.
In addition to weight reduction, Zytek emphasized powertrain system efficiency, with the goal of maintaining an air-cooled topology for the motor, inverter and battery. This further reduces vehicle weight and brings with it added advantages in powertrain packaging flexibility.
The total weight of the motor, inverter and gearbox is less than 50 kg (110 lbs), approximately 45% of that of a comparative, current production, water-cooled drivetrain with its associated radiator, cooling fluid, pumps etc. This light weight contributes to the low overall vehicle weight while the highly compact size means that luggage space can be increased compared to the regular internal combustion engined vehicle.
Added benefits from the highly compact electric drivetrain mean that as less material is used in the manufacture of the electric machine, the carbon footprint associated with the manufacture of each drive is very low. The close relationship with Vocis, and the tight integration of their high-efficiency, light-weight EV gearbox allowed significant optimization of both the motor and the transmission.
The second iteration of drivetrain design also saw the introduction of Zytek’s first Li-ion battery pack. Following 12 months spent selecting a suitable Li-ion cell design, CFD analysis of multiple cooling system options, design of a new pouch cell frame incorporating cooling channels and the design of a new Battery Management System, Zytek has manufactured a highly optimized, lightweight high-voltage electric vehicle battery pack.
This pack has undergone testing to ensure its safety in this prototype application, including a variety of cell, module and battery tests. These tests have assessed thermal characteristics, plus cell performance under extremes of electrical and mechanical abuse.
With low vehicle weight being a primary project target, every effort was taken to design and integrate the battery into the vehicle, and as such a single structure has been used, improving on the more traditional “box within a box” approach, Zytek said. This yielded a total battery weight of 129 kg (284 lbs).
The battery capacity of 12.1 kWh, coupled with the lightweight vehicle and powertrain design, has exceeded range targets, giving more than 100 miles over the New European Drive Cycle (limited to 100 km/h), and up to 130 miles over the urban European Drive Cycle (ECE15).
Zytek has designed and integrated electric drive systems for a wide range of European and US vehicle manufacturers and is currently building high-performance electric drivetrains up to 70 kW and 300 N·m for cars, buses and light commercial vehicles. Their UK facility can accommodate up to 6,000 E-Drive integrations a year in batches as low as 100. Zytek can also manufacture up to around 18,000 high efficiency electric traction motors each year, with the option of integrated control systems to further improve overall system weight and packaging.
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