The operating principle of HSTs is simple: a pump, connected to the prime mover, generates flow to drive a hydraulic motor, which is connected to the load. If the displacement of the pump and motor are fixed, the HST simply acts as a gearbox to transmit power from the prime mover to the load. The overwhelming majority of HSTs, however, use a variable-displacement pump, motor, or both - so that speed, torque, or power can be regulated.
HSTs offer many important advantages over other forms of power transmission. Depending on its configuration, an HST:
- transmits high power in a compact size
- exhibits low inertia
- operates efficiently over a wide range of torque-to-speed ratios
- maintains controlled speed (even in reverse) regardless of load, within design limits
- maintains a preset speed accurately against driving or braking loads
- can transmit power from a single prime mover to multiple locations, even if position and orientation of the locations changes
- can remain stalled and undamaged under full load at low power loss
- does not creep at zero speed
- provides faster response than mechanical or electromechanical transmissions of comparable rating, and
- High sensation and accuracy in adjusting
- High stability in motion of actuator
- Smooth control and safety
- Ease and accuracy of control: By the use of simple levers and push buttons,the operator of a hydraulic system can easily start, stop, speed up and slow down.
- Multiplication of force: A fluid power system (without using cumbersome gears, pulleys and levers) can multiply forces simply and efficiently from a
fraction of a kilogram, to several hundred tons of output.
- Constant force and torque: Only fluid power systems are capable of providing a constant torque or force regardless of speed changes.
- Simple, safe and economical: In general, hydraulic systems use fewer moving parts in comparison with mechanical and electrical systems. Thus they
become simpler and easier to maintain.
Disadvantages
- Because of working with High pressure, it is difficult to seal
- Require high quality of oil
- Handling of hydraulic oils which can be quite messy. It is also very difficult to completely eliminate leakage in a hydraulic system.
- Hydraulic lines can burst causing serious human injuries.
- Most hydraulic fluids have a tendency to catch fire in the event of leakage,
especially in hot regions.
In the hydrostatic transmission there are three main components:
- Hydraulic pump
- Hydraulic motor (cylinder)
- Controlling and adjusting components (various valves)
A pump is required to push the fluid. An actuator is the output of the system. Besides a
pump and actuator, the
system also requires valves to control the fluid flow; a reservoir to store the fluid and supply it to the pump; connecting lines; and various hydraulic accessories.
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