Fig. 4. The battery-electric Delta E-4 Coupé is a two-door, four-seater, pure electric car with a range of 320km.
Other organisations have also been investigating automotive drive trains that minimise the use of rare-earth magnets. Around one year ago Drive System Design (DSD) and Oxford Yasa Motors introduced the MSYS Multi-Speed Traction System for electric vehicles. This compact, lightweight (45kg), integrated, three-speed system supplies 60kW of continuous power and more than 200Nm of torque. The overall powertrain efficiency is claimed to be better than 91 per cent.
Segmented armature
The MSYS axial flux Yasa (yokeless and segmented armature) motor and multi-speed transmission are said to provide car designers with opportunities to simplify the motor cooling system, electrical architecture and control system. Moreover, the car’s drivability is enhanced by the drive system’s high torque even from low motor speeds, and the DSD electrically actuated Overlap Shift Technology provides rapid gear changes. While the motor is rated at 60kW continuous, a peak of 85 kW or more can be sustained for periods of up to 60 seconds (Fig. 2). Oxford Yasa Motors has already built a reputation for
its motors, with four Yasa 750 motors - with 750Nm peak torque each - being installed in the Lola-Drayson B12/69EV pure electric Le mans prototype; one of the same motors has also been used in the Ion Horse electric motorcycle prepared for the Isle of Man’s TT Zero race, two are in the Westfield iRacer (Fig. 3), and two in the Delta E 4 coupé (see panel). Another company heavily involved in SR motors is Switched Reluctance Drives Ltd (SRDL), which is a subsidiary of Japanese company Nidec Corporation. SRDL says it has pioneered the development, application and commercialisation of SR technology under its SR Drive trademark and is now a world leader in this area. The company was founded in 1980, having grown out of fundamental research work carried out at two UK universities, namely Leeds and Nottingham. SRDL explains that its SR Drive system comprises a
simple variable-speed brushless motor with a dedicated electronic controller. Torque is produced by the magnetic
56
www.engineerlive.com
attraction of a steel rotor to stator electromagnets. No permanent magnets are needed - either of the conventional or rare-earth type - and the rotor carries no ‘squirrel cage’ or windings. Low energy losses in both the rotor and power electronics eases thermal management and enhances reliability and efficiency, while the compact stator windings permit great flexibility in terms of the motor’s shape. In the immediate future there may be no alternative
to servo motors and other high-performance motors incorporating rare-earth magnets, other than the motors highlighted above. As manufacturers seek alternatives, however, demand for rare-earth magnets will fall and there may be a reduction in prices - but it would be imprudent to rely on this happening. There is plenty of research underway in the field of motors for electric and hybrid vehicles, but it is less clear what the level of research is in relation to servo motors for applications such as industrial automation. Design engineers therefore need to stay up to date with the latest developments, as it is likely that volatile pricing will continue to be the norm for rare-earth magnets for a few years yet
Delta E-4 coupé
Delta Motorsport launched the battery-electric Delta E-4 Coupé in May 2011 (Fig. 4). Designed from the outset as a pure electric vehicle, the two-door, four-seater’s light weight and high-efficiency systems mean it has a range of 320km (200miles) on a single charge, yet it can accelerate from zero to 96km/h (60mph) in less than five seconds. The key to the E-4 Coupé’s impressive performance
and range is said to be the close integration of the various technologies. The new carbon composite chassis weighs just 85 kg, which is around one-third that of a comparable steel structure, despite being designed to pass EU crash tests. Each of the two high-performance direct-drive Yasa 750 motors produces 100kW of peak power, while only weighing 23kg. Installing the batteries under the floor aids the sporting handling characteristics and helps to minimise aerodynamic drag. ●
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68