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World-first Non-hydraulic multi-speed auto transmission for ev

Bygen Transmission‘s info & technology
Produt Story
Produt Story
Open New Horizon: EV Cheaper Than ICE
In-wheel Transmission (5-speed Auto),
Driving Range Increase Double for the first time in the world
Bygen developed multi-speed auto transmission without complexity of hydraulics, which is core and original technology to extend driving range of electric vehicles. This results in lowering sales price of EVs.

Bygen's In-Wheel transmission, which is directly connected to motor with one axle, can be equipped to each tire without other drive axles. Without hydraulics, net weight and measurements are 1/10 lighter and smaller than traditional transmission.

Because electric motor efficiency is over 90% comparing to 30% of internal combustion engine, motor has replaced engine for industrial machinery. Electric vehicles are called eco-friendly owing not only to environment-friendly battery but also to higher efficiency of motor.

Despite subsidy from governments and smaller number of parts, still higher sales price of EV is the biggest barrier for electric vehicle to penetrate automobile market. Expensive battery price, which consist of almost 60% of total cost (as for EV with 60kWh battery for 300km driving range per a single time charge), is the biggest hurdle to lowering sales price of EV. Increasing drive range is directly connected to lowering sales price.

While motor efficiency is higher over 90%, it is lower out of the rated RPM regime. Transmission allows the motors to be smaller and more efficient by running it in a more power efficient regime (rated RPM range) of the electric motor at any speed spectrum. For this reasons, multi-speed transmission is under developing by all EV participants.

(refer to energy efficiency graph of motor)


Adding transmission to electric automobiles is largely due to motor efficiency. For single speed drives the motors must have a high speed range in order to allow low speed maneuvering and high speed highway cruising. This results in lowering efficiency of motor, which leads higher capacity of battery and more expensive manufacturing costs.

The reason why electric mobiles do not require transmission is motor can deliver high torque at zero RPM to start vehicles, can cover wider speed range to run vehicles, and can deliver peak power in wide speed range. However, stall torque and high speed running torque consume strong current. Multi-speed transmission mechanically supplies adequate torque at each speed to save battery (current).

Multi-speed transmission in internal combustion engines (ICEs) makes automobile to run at rated RPM regime at any speed to save fuel energy (In case of middle-class cars, it runs aroung 2,000 RPM). Including CVT, current transmissions of ICEs use hydraulics to hold in gears and clutch, which is too big and heavy to be used for EVs. Bygen's uniqueness and originality is at this points. Bygen's In-Wheel transmission is small and light enough to be directly connected to wheel. Nobody can success to do this.

Bygen tested its In-Wheel transmission to apply to 2-wheel motorcycle with the cooperation of Department of Mechanical and Automotive of Seoul National University of Science and Technology (SeoulTech). We equipped two transmissions and two motors (750 watt each) at front and real wheel, independently. Comparing single speed e-motorcycle ("G") had 3.8 KW motor. Max speed and grade ability with continuous speed of Bygen's and "G"'s were 63km/h, 62km/h, and 20.9%, 14.1%, respectively. Comparing driving range with constant speeds, efficiency of Bygen's was 50 to 100% higher than "G"'s at each constant speed. At road test in Seoul, Bygen's run 102km for 5 hours with 2.4kWh battery, which was double of "G"s.

(please refer to official test report from SeoulTech)


We would like to express the gratitude to Prof. In-Yong Ohm and his team for giving us the awesome opportunity to work on this test. His valuable insight helped us a lot in improving the quality of this work.


Besides prominent test results, it is expected commercial model will show more efficient performances, because vehicle with wider speed range requires multi-speed transmission to cover inefficient higher speed range.

Outstanding test results with higher efficiency can be explained by optimized battery consumption for using In-Wheel transmission(4-speed auto), which run the motors at rated RPM regime at any speed range. Also, In-Wheel transmission of Bygen, which directly run wheels without connecting axles, does not use another power to operate hydraulics to lose energy. For these reasons, Bygen's In-Wheel transmission makes it possible to use smaller motor for performing same torque and speed, which contributes to use less current.

Developing Disruptive Transmission Technology from 2010,
Considering upcoming new era for electric vehicles, marketable price for EVs is the biggest hurdle to overcome. Transmission efficiency would play the key role to improve energy efficiency to reduce electric consumption.

It is expected that PMDC motor will be used with transmission for higher efficiency, lower price, and easy controlling. Water cooling system will be useless for lowering overheating at higher speed, because motor with transmissio will run at rated RPM range at each speed.

Bygen's In-Wheel transmission will act for cutting manufacturing cost by over 30%, which will lead EV price to be competitive to traditional vehicles. Bygen will endeavor to extend this transmission technology's application into new sectors such as drone and windmill.

Manufacturing technology should be fundamental base for developing so-called "4th industrial revolution which combine all hi-tech including IT, AI, Things Internet, etc.. Bygen's original and unique transmission technology will take significant role to support environmental-friendly EV manufacturing industry. I would like to acknowledge the support and sincerity of my colleagues and their family of Bygen, who showed the deepest understanding and endured patiences for developing time. Bygen's In-Wheel transmission is a meaningful product combining disruptive technology to be invested US$ 10 million and warmhearted understandings to be endured.

In consideration of the increase in trend of fewer passengers, especially for commuters, Bygen is developing 3-wheel compact vehicle for two passengers. with total length between front and rear wheels of 1.1m and total weight of 300kg, the 3-wheel vehicle (one front wheel and two rear wheels) will have Bygen's In-Wheel transmission separately, which will give smooth cornering for low tilting point and in-wheel type.
Target sales price should be below US$10,000. Lowering production cost will
contribute to the rapid growth of EV market.

Disruptive technology is not made by one-time inspiration,
but by endurance and dedications. All historically meaningful technology
has bee born by accumulated skills and painful experiments for several times.