|Compared to a single-speed EV or HEV transmission, DSD’s MSYS 3-speed system provides a 40% weight saving and 10-15% lower energy consumption. Click to enlarge.|
UK-based Drive System Design is developing a new EV powertrain based on an alternate approach to powershifting (no torque interrupt) achieved by separating the existing functions of a synchronizer. The integrated design of an axial flux YASA motor (earlier post) with the multi-speed transmission contributes to simplification of the motor cooling system, electrical architecture and powertrain control system.
The MSYS system can mean a 10-15% improvement in the range of electric vehicles, the company says. (Earlier post.) The company was recently showcased at the Cleantech Innovate 2014 event by the UK’s LowCVP organization (Low Carbon Vehicle Partnership), along with 7 other companies. DSD was the winner of a LowCVP commendation as the most impressive of the road transport-focused entries.
(DSD is participating in the Evoque_e research program (earlier post) to develop new modular hybrid, plug-in hybrid, and battery-electric vehicle (BEV) technology. The pure electric research vehicle will the MSYS multi-speed traction system developed.)
The company’s Technical Director, Alex Tylee-Birdsall, is presenting a paper entitled “High efficiency electric vehicle powertrain” at the Future Powertrain Conference (FPC2014) at the National Motorcycle Museum in Solihull, UK tomorrow.
MSYS supplies 55 kW of continuous power (100 kW peak for 60 seconds) and more than 2,000 N·m (1,475 lb-ft) of torque at the wheels in an extremely compact package with more than 91% total electric powertrain efficiency (98% transmission efficiency). MYSYS weighs just 55 kg (121 lbs).
MSYS offers 3-speed gearing with powershifting; the ratios are:
Rapid ratio shifting using DSD Overlap Shift Technology minimize torque interruption. The powershift elements in the MSYS transmission separate the two basic synchronizer functions of friction and latching and use the enhanced friction capacity of multi-cone clutch assemblies to provide an uninterrupted flow of torque to the wheels while using no energy to hold the transmission in gear.
|Each ratio of the MSYS transmission uses its own multi-cone friction clutch to transmit drive during shifting and a separate dog clutch to latch the assembly in gear. Click to enlarge.|
The increased friction capacity allows the powershift cone clutch to temporarily drive the vehicle during shift events while latching in gear is achieved by dog clutches with self-locking teeth, similar to a conventional synchronizer.
There is growing recognition of the benefits of multiple ratios for EV transmissions. DSD has taken a unique approach by developing a reliable, highly efficient, seamless gearshift in order to make such transmissions acceptable to the user.
MSYS avoids the disadvantages inherent in other transmission options. A DCT consumes energy continually to maintain clutches in the open or closed position (depending on clutch type); an AMT suffers from torque interruption during shift events, and automatics based on epicyclic gear sets add complexity, cost and drag.
By using proven technologies in a unique arrangement, i.e. synchronizer-derived cone clutches and dog clutches, DSD has been able to seek patent protection for the system while minimizing the technical risks during development and enabling system suppliers to make use of their existing expertise.
Enhanced friction levels have been achieved in the multi-cone clutches by using forced lubrication with variable flow through the clutch packs. Flow variation permits good thermal management at times of high slip with maximum efficiency at times of lower demand.
Characterization testing of the cone clutches has shown good linear engagement properties (torque vs applied pressure), enabling the clutch-to-clutch shifting that is an essential part of the MSYS design. The next phase of development will include installation of a prototype transmission in a demonstrator vehicle, allowing calibration to commence. The vehicle will be ready for demonstration to customers during the summer of 2014.
MSYS will be ready for series production during Q4 2016, to support the growing demand from vehicle manufacturers needing to comply with increasingly tight CO2 emissions regulations. A family of MSYS powertrains with different power and torque outputs is planned, to suit the requirements of different target sectors.