A novel compact 18-speed transmission for personal mobility vehicles


Currently, electric cars and plug-in hybrid electric cars are thought to be good solutions for relieving exhaust gases and traffics.

However, there are still insufficient regulations, policies, and infrastructures for such vehicles.

Personal mobility vehicles, such as electric wheelchairs, e-scooters, hybrid bikes, fixie bikes, and folding bikes, provide a new solution.

These vehicles can be used by people of all ages for short to intermediate distance travel. In addition, they can reduce the risks and costs of daily commuting and make people less stressed and more relaxed.

In a study newly published in the International Journal of Automotive Technology, a South Korean scientist develops a novel 18-speed transmission for personal mobility.

The small-sized transmission is an internally geared hub transmission. The gear trains are made of a couple of simple and double pinion epicyclic gears. Each gear is contacted with the shaft that connects to the wheel hub.

The transmission has 3 epicyclic gear modules: two 3-speed modules and one 2-speed module. Each gear module has 2-3 epicyclic gears.

The transmission can make distinct gear steps up to 18 by connecting the three epicyclic gear modules serially. Like a conventional transmission, the shift can be initiated by a cable or electric motor.

Because the transmission is made of tiny mechanical elements in a complex structure, the researcher tested its feasibility and operating principles. He used the Automated Dynamic Analysis of Mechanical Systems (ADAMS) software to build a numerical model of the transmission.

With this model, several simulations were carried out to analyze its dynamic behavior. One performance evaluation was the automatic and robust shift functions at any circumstances.

In order to validate the transmission’s performance experimentally, the researcher built a prototype and a test bench. The test bench was composed of various instruments for measuring torque and the rotational speed of the prototype.

The test showed that the maximal power transmission efficiency is obtained as 96% at the final gear step. This means the transmission can automatically shift in full 18 gear steps and shift mechanism works as expected.

The finding suggests that the new 18-speed transmission is distinguished from other transmissions for its small size, lightweight, high efficiency, and wide speed range up to 18 gear steps. Future work will test this transmission in personal mobility vehicles.

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