Hydromechanical transmission (HMT)
A hydromechanical transmission (HMT) is an automatic transmission that uses a hydraulic torque converter and mechanical planetary gears to change the transmission ratio.
Components
The main components of the GMF include:
*Hydraulic Torque Converter: Provides a smooth connection between engine and transmission, multiplying torque at low rpm and acting as a fluid coupling at high rpm.
*Planetary Gear: A manual transmission consisting of a set of planetary gears, a sun gear and a ring gear that are used to change the gear ratio.
*Hydraulic block: Contains the valves and passages that control hydraulic flow in the transmission to allow gear shifting.
* Electronic Control Unit (ECU): Controls the transmission, including shift timing, torque converter lock-up and other functions.
Operating principle
GMP works as follows:
1. The engine drives a hydraulic torque converter, which is connected to a planetary gear.
2. At low speeds, the torque converter multiplies the engine’s torque, allowing the vehicle to move away smoothly.
3. As engine speed increases, the torque converter locks, providing a direct mechanical connection between the engine and transmission.
4. The hydraulic unit uses oil pressure to operate valves that change the position of the planetary gears, changing the gear ratio.
5. The ECU monitors various parameters such as engine speed, vehicle speed and throttle position to determine the optimal gear shift point.
Advantages
GMPs have the following advantages:
* Smooth Gear Shifting: Hydraulic torque converter ensures smooth shifting without jerking.
* Durability and Reliability: Hydraulic components and planetary gears are designed to withstand heavy loads.
* Automatic gear shifting: The driver does not operate the gearbox manually, but shifts it automatically depending on driving conditions.
* Towing Capability: Some GMPs are designed to tow heavy loads.
Flaws
GMF also have some disadvantages:
*Power Loss: The hydraulic torque converter causes some loss of engine power.
* Fuel consumption: GMTs are generally less fuel efficient than manual transmissions.
* Complex repairs: Repairing GMP requires special knowledge and equipment.
* Restricted Engine Braking Effect: The torque converter limits engine braking effect, which may make the vehicle difficult to control on steep inclines.