56 MOTORS AND DRIVES
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To make the best use of the limited supply of electrical energy, the bike is equipped with a high- efficiency Lynch axial-gap dc motor. This type of low-voltage, high-torque, permanent-magnet dc motor has the added advantage of a high power density. Lynch motors are today manufactured in the UK by the Lynch Motor Company in three frame sizes and with numerous options. Alternatively two motors can be coupled together to drive a single output shaft, thereby increasing the power available. To illustrate the motors’ capability, the LEM 130 model 95s has a rated power of 3.02kW, rated torque of 4.35Nm and rated speed of 6624 rpm. Peak efficiency is 87 per cent. For more demanding applications, the LEM 200 model D135 has a rated power of 14.39kW, rated torque of 36.4 Nm and rated speed of 3780 rpm. Peak efficiency for this model is 90 per cent.
Motorcycle applications
Cedric Lynch, inventor of the Lynch motor, now works with Agni Motors in India. Here he has further improved the design for applications in the domestic, leisure, industrial, commercial, agricultural and marine industries. The latest version of the Agni Motor is said to offer higher torque per amp and lower speed per volt, which makes it possible to use a simpler and cheaper transmission in some applications, as well as being slightly more efficient (Fig. 2). Two Agni motors are being installed in a Ducati 600 Supersport, which is intended to be the fastest, road- legal, emission-free motorcycle in Europe. Power will be supplied by a LiFePO4 (lithium iron phosphate) battery developed by Lifebatt. The bike will be entered in the TTxGP clean-emissions race, which takes place on 12 June 2009 on the Isle of Man TT circuit, one of the most gruelling road-race circuits in the world. In the USA, Briggs & Stratton has licensed Lynch
motor technology to manufacture the Etek motor for use primarily in electric outboard motors for boats. Once again, however, this type of motor has also been selected for use in motorbikes. This time the company is Electric Motorsport of the USA, with its Electric Motorsport GPR-S (Fig. 3) using 3.3kWh Lithium batteries rather than the fuel cell of the ENV. The GPR-S is claimed to
have a maximum speed of 112 km/h (70mph) and a range of 80km (50miles). While the bike is equipped with the Etek-RT motor, the company says that the industry-standard motor mounting would make it straightforward to retrofit a different motor (and controller) to take advantage of regenerative braking. An alternative to the
Fig. 3. The Electric Motorsport GPR-S uses Lithium batteries to power a Briggs & Stratton Etek-RT motor and achieve a maximum speed of 112km/h (70 mph).
In-wheel motors
PML Flightlink has been manufacturing printed armature motors (or ‘pancake’ motors) for some 40 years. In this type of motor, the flat armature is essentially an ironless disc with coils punched from sheet copper and formed onto non-magnetic disc insulators. Brushes contact on two or more points to create a path through the copper, thereby creating a magnetic field that interacts with the permanent magnets to cause motion. With no magnetic material present in the armature,
‘cogging’ is eliminated, resulting in smooth operation and continuous torque down to standstill, with minimal torque ripple. Torque is proportional to current and not limited by saturation, and speed is directly proportional to voltage.
Furthermore, the ironless armature has virtually zero inductance, which is beneficial in that when the magnetic field collapses, energy does not discharge by arcing to the brushes. Consequently the printed armature exhibits low EMC properties and brush wear is minimal. Indeed, PML claims to have achieved over 10 000 hours working life on a high-volume product. Recent developments from PML Flightlink include
the Hi-Pa Drive in-wheel unit that incorporates the motor and drive electronics within a common housing for automotive drive applications. This has already been applied to the Mini QED and the Volvo ReCharge. Scaling this concept down, the company has also created the Nano Wheel that incorporates a brushless motor within a wheel hub.
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Lynch, Agni and Etek motors is the PMG 132 high-performance disc armature motors (Fig. 4) from Perm Motor in Germany, which operate from 24-72V and have a rated power output of 2.2 to 7.2kW. Depending on the operating conditions, these can achieve a peak efficiency of 90 per cent or more.
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