Drive System Design Develops Range-Increasing 3-Speed Transmission For EVs
Drive System Design, an engineering consultancy specialising from UK, recently unveiled at the CTI Symposium in Berlin technical details of its novel transmission for hybrid and electric vehicles called MSYS.
It has 3 speeds and, according to Drive System Design, will makes EVs and HEVs better.
“By making fundamental changes to synchroniser layout that allow smoother shifts with higher efficiency, DSD has been able to provide a multi-speed transmission with a 40 percent weight saving and 10-15 percent lower vehicle energy consumption compared to a single-speed EV or HEV transmission.”
10-15% higher efficiency is of course welcome but the cost and weight will be higher as well compared to single-speed, so we are still waiting to see if some automakers will use a multi-speed gearbox in its plug-in vehicles.
By the summer, DSD plans to build a demonstration vehicle and would like to be ready with series production by Q4 2016.
Seamless shifting is possible thanks to use multi-cone clutch and is described as follows:
“The powershift elements in the MSYS transmission separate the two basic synchroniser 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. 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 synchroniser.”
“By using proven technologies in a unique arrangement, i.e. synchroniser-derived cone clutches and dog clutches, DSD has been able to seek patent protection for the system while minimising 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.”
DSD technical director, Alex Tylee-Birdsall stated:
“The main consumer concern holding back sales of electric vehicles is range anxiety. By using an MSYS multi-speed transmission, energy consumption can be improved by up to 15 percent which translates directly into increased range. It permits downsizing of the motor and, by being in the optimum gear ratio more often, extends the time the motor spends operating at high efficiency.”
100 kW drivetrain consisting of a YASA motor and MSYS has 91% overall efficiency – about 98% for transmission and 93% for the motor. Its weight is 67 kg (148 lbs) from which 55 kg is MSYS, which sadly is a significant value.
Prototype specification of MSYS with YASA motor:
MSYS is a next generation powertrain for electric vehicles. The heart of the system is an alternate approach to powershifting (no torque interrupt) achieved by separating the existing functions of a synchroniser
The system supplies 55 kW of continuous power and over 2000 Nm of torque at the wheels in an extremely compact package with over 90% total electric powertrain efficiency. A low cost, high efficiency unit, weighing just 55kg including motor, MSYS offers a powerful and efficient powertrain solution to the electric vehicle market. The integrated design of an axial flux YASA® motor with the multi-speed transmission has led to simplification of the motor cooling system, electrical architecture and powertrain control system.
The full specification is:
- Rating: 55kW continuous, 100kW peak (for 60 seconds)
- Motor torque: 200Nm
- Output torque: 2000Nm
- Efficiency: 91% overall, 98% transmission only
- Mass: 55kg wet, including motor (12kg)
- Gearing: 3-speed with Powershifting
- Ratios: 1st 10.01:1, 2nd 7.15:1, 3rd 5.42:1
- Cooling: integrated pump and radiator
- Park lock: integrated plunger type with electric actuation
The low cost is due to the use of:
- Minimised rare earth material content
- Simple actuation system
- Novel motor construction
- Integrated cooling system
The high efficiency is due to the use of:
- Low inductance motor
- Minimised power electronics demand
- Dry sump lubrication
- High efficiency bearings
The low weight is achieved by using:
- Low motor weight (12kg)
- Light weight materials
- Compact and integrated design (approx. 300x300x400mm)
MSYS also features rapid ratio shifting using DSD Overlap Shift Technology to minimise torque interruption.