Multi-Speed Transmission Mechanism Using a Compound Planetary Gear Set and Brakes

Today, the use of electric vehicles (EVs) is increasing. Electric motors, which are used as the power source in EVs, have better torque-speed characteristics than traditional engines. However, electric motors also have a low speed torque limitation; moreover, their energy efficiency at low speed is not very high, resulting in severe heat generation when climbing steep slopes. While it is better to use multi-speed transmissions in EVs, the complex structure of conventional multi-speed transmissions decreases the advantages of EVs. This paper proposes a multi-speed transmission mechanism that uses a compound planetary gear set and brakes; its simple structure and lack of a synchronizer make it suitable for EVs. The electric motor's high controllability makes high-speed gear shifting possible because the motor's teeth are always engaged. It is also possible to throw the motor out of gear or to put the brake on the output shaft. General equations for the reduction ratios are derived and a design possibility for the arbitrary reduction ratio is mentioned. A simple experimental setup is presented, demonstrating that the proposed multi-speed transmission mechanism is effective.