© Vocis 2010
Vocis Ltd were the project lead for one of the final five winning projects featured here with funding from the Niche Vehicle Network competition, annouced at LCV2012 for its 4-Speed Electric Minibus concept.
In partnership with Zytek Automotive, a specialist powertrain and vehicle engineering company and the University of Surrey, it aims to build a demonstration vehicle for the Vocis 4 Speed dual motor transmission - known as ‘eDCT’ (electric Dual Clutch-less Transmission).
Vocis specialise in control systems software, hardware, actuation hardware, prototype transmission design and build, vehicle applications and calibration for driveline systems.
Since late 2006 Vocis has been part of Turin-based Oerlikon Graziano Drive Systemsand can offer solutions together with or independently of Graziano involvement.
Significant update to second electric Mercedes Vito demonstrators
Two years ago Vocis and Zytek demonstrated - at LCV2010 - a prototype electric version of the Mercedes Vito configured as a taxi, also part-funded by the UK Government’s Niche Vehicle Research & Development Programme.
The E-Vito taxi used a 70kW version of Zytek’s electric drivetrain and a single speed custom-designed Vocis gearbox.
According to Mike Everitt, Managing Director, Vocis Driveline Controls “The first project that we did was the eVito Taxi with a single speed transmission as shown at LCV 2010."
"Then, we carried out a second programme and made another vehicle, an eVito Minibus with a two speed seamless shifting transmission. Zytek were the lead partner in both projects, our role in the first was modest, our role in the second was much larger as one of the prime project aims was the application of the two speed transmission, which is known as 2SED - ‘2 Speed Electric Drive’. The eVito Minibus was shown at the LCV 2011 show at Rockingham."
"Both the Taxi and the Minibus vehicles are configured as a front wheel drive. The standard Vito is rear wheel drive."
"It is this Minibus vehicle that we are now using as the base for the eDCT installation. On this occasion we'll install the transmission in the rear to drive the rear wheels. We aren't removing the 2SED transmission, we'll simply isolate it so the vehicle becomes dedicated to the eDCT programme."
"After this project is complete, as per the current definition, we have a longer term objective to reconnect the 2SED transmission and be able to simply ‘flick a switch’ and be able to change between driving the vehicle in 2 speed FWD mode or 4 speed RWD mode. Further even to this we could even configure the vehicle to operate as a 4WD, but this is a nice-to-do bonus not a prime objective."
The design concept
The design concept for the eDCT was for improved performance and efficiency, with seamless shifting and avoiding the complexity and cost of a conventional powershifting transmission. The solution was a mechanical design controlled by a reduced set of transmission control software.
The eDCT design is sold as simple and modular - as it does not require clutches and synchronisers, and can have motors located at opposite sides of the gearbox or the same side. This helps make it a cost effective solution for the automotive market.
Up to 15% reduced battery drain for greater range
“Our four speed transmission design is smaller and allows the use of much smaller electric motors that uses less very expensive rare earth magnetic materials. Plus, with more gear ratios it makes more efficient use of power from the battery. So it offers greater range, higher top speed, acceleration and ability to operate on much steeper gradients etc.” claimed Mike Everitt.
“We think it will be capable of offering 8-15% more range than a single speed, depending on the drive cycle used for the comparison. We don't have explicit data for this vehicle as yet but for a 100 mile range vehicle it will extend to 108 to 115 miles - alternatively the vehicle could be fitted with a smaller battery and achieve the same range. Battery cost is a major driver in the cost of EVs’.
As stated by Oerlikon Graziano, most current EVs use a single-speed transmission, relying on the electric motor’s torque spread to provide adequate performance. However this means the motor spends much of its time operating at only 60 to 70% efficiency. Oerlikon Graziano’s new transmission instead uses two smaller motors and provides four speeds to keep the motors running closer to their peak efficiency of approximately 90%.
The transmission uses two input shafts, each driven by an electric motor. The concept is similar to a DCT but using two motors in place of the twin clutches: one motor drives a shaft that carries first and third gears, the other drives a shaft carrying second and fourth. This allows pre-selection of the next gear before the previous one has been disengaged, using the two motors to synchronise shaft speeds so no synchronisers are needed. Following gear selection, the drive torque transfers seamlessly between the motors to complete the shift. Different strategies prioritise economy or performance and the transitions between the two.
The shift control system was developed by Vocis Driveline Controls, itself part owned by Oerlikon Graziano. Having considerable prior expertise with DCT applications, Vocis used a range of algorithms within their software to cover driver strategy, shift sequencing, gear actuation and safety functions complying with OBDIIrequirements.
The images (above) from Vocis, “show the transmission, without its motors attached. There is a motor mounted on either side, the first one is mounted to drive gears 1 & 3, the second to drive motors 2 & 4.”
Showcase for the company's Dual Clutch-less Transmission
The purpose of the minibus project is as a demonstrator for potential clients of the eDCT in use.
“The funding is very useful and welcome”, according to Mike. “The project also has a dual benefit. It’s helps us develop the technology with the partners and is useful for marketing. It means a potential customer can drive our products.”
“Our longer term aspiration for a third stage of this project,” said Mike “is to be able to use this eVito Minibus to develop and demonstrate both our 2SED 2 speed and our eDCT 4 speed transmissions in the same vehicle at the flick of a switch. The current 2SED driving the front wheels, the eDCT driving the rear wheels."