Page 10 - Materials Australia - April 2019

MATERIALS AUSTRALIA
WA Branch Technical Meeting – 11 March 2019
New innovations in Continuously Variable Transmissions (CVTs)
Source: Jochen Franke, Managing Director, ATSH Ltd and Treadlie Engineering Pty Ltd
At the recent Western Australia branch meeting, Jochen Franke (Managing Director, ATSH and Treadlie Engineering) provided an engaging and thought provoking presentation.
Franke is well known as the inventor
of the ScanalyseTM system, used for the measurement of grinding mill profiles. After the successful commercialisation
of this technology, now known as the Outotec MillMapperTM, Jochen turned
his mind to Continuously Variable Transmissions (CVT). These are widely used in motor vehicles, where they transmit power though a vee-belt running between two pulleys, which take the form of opposing cones. As the belt is forced sideways it climbs up one cone and down the other, altering their effective diameters and hence the gear ratio. However, because the belt has to move sideways, such CVTs are relatively wide. This precludes their use in some applications, such as bicycles, in which the allowable width is limited by human anatomy. Thus, the challenge that Jochen took on was to design and build a narrow variable diameter vee-pulley.
Jochen’s initial training was in spatial science and photogrammetry; this might be an explanation for his exceptional ability to visualise movements in three- dimensional rotation. Fortunately for
the audience, he illustrated the way in which the patented mechanism works with video and animations. Diagrams can also be seen on the website: www. treadlieengineering.com/cvt-drive-train/
As a way of describing how the variable diameter pulley works, try picturing two imaginary disks, a little further apart than the width of the vee-belt; these define the working space within which the belt is confined.
Just outside this space, on either side, sits a nest of concentric chamfered annular rings. These chamfered rings can be moved sideways, sequentially and
in opposing pairs, into (or out of) the working space. The chamfered faces of each pair of opposing matching rings form the vee-shaped surface that grips the belt.
As the currently working pair of rings is
simultaneously moved further inwards, the vee-groove closes and forces the belt further from the axle shaft, increasing the effective pulley diameter. This provides
a continuously variable diameter. When the maximum movement is reached for this pair of rings, the next opposing pair of rings is brought into action, extending the range of continuously variable pulley diameter. All rings that are smaller than the current working ring remain in the working space.
Thus, instead of operating the scroll mechanism with a separate electric motor, Jochen’s team has developed an in-built spring-loaded actuator to control the output pulley diameter. Through a combination of finite element analysis and direct testing at Curtin University, the team established the optimum range of friction coefficients for the belt and pulley ring surfaces that allow this mechanism to operate with high power transmission efficiency.
The working prototype pulley assemblies are made from aluminium alloy, with each annular ring divided into smaller segments, each separately moved by the scroll mechanism. From a materials point of view, an optimal selection is needed for the material, or composite material system, that will allow low- cost manufacture, durability and reliable friction coefficient for the chamfered segments, while not needing lubrication. Jochen is working with CSIRO to achieve this; members of the audience had suggestions as to what might be worth investigating further.
Jochen’s immediate commercialisation target turned out to be a market that few in the audience were aware of. This is the field of ‘cargo bikes’ and ‘pedalecs’. Pedalecs are low-powered electric-assist bicycles that are classified are bicycles
in many jurisdictions. Cargo bikes are widely used in Europe by delivery companies, such as DHL, for ‘last mile’ delivery of parcels in densely populated cities. Being classed as bicycles, they have fewer parking restrictions and can travel in designated areas, avoiding road congestion.
Compared with human-powered bicycles, a smaller gearing ratio is sufficient, the additional weight over a convention multi- gear chain drive system is not significant, and the whole drive system can be fully enclosed. The next development objective is integration of an electric pedal-
assist drive motor within the variable transmission system.
Once again, this Materials Australia technical meeting highlighted extraordinary developments that are proceeding ‘under the radar’ in Western Australia.
10 | APRIL 2019
WWW.MATERIALSAUSTRALIA.COM.AU
Photo L-R: Louise Petrick, Jochen Franke
In order to move the segments sideways into and out of the pulley space while the whole pulley assembly is rotating, Jochen has designed a scroll and cam mechanism actuated by a small wirelessly controlled electric actuator motor inside the pulley wheel.
The width of the whole assembly is around five times the width of the belt, regardless of the gearing ratio, which
is governed by the number of nested moveable annular rings. In the working prototype, fitted to custom-made bicycle, the pulley wheel diameter varies over
a range of around 2:1. Thus, working together, the drive and the driven pulleys allow a roughly 4:1 variable gear ratio.
Jochen then explained that while it took 18 months to develop the drive pulley, another 18-month period was needed for the output pulley. The challenge was to avoid the need to exactly synchronise the diameters of the two hubs, which are connected only by the flexible pulley.