## Why are Hydrostatic Transmissions in Cars?
Hydrostatic transmissions (HSTs) are a type of power transmission system that uses hydraulic fluid to transmit power from a prime mover to a driven load. HSTs are often used in industrial and agricultural applications, where they offer a number of advantages over traditional mechanical transmissions.
Advantages of Hydrostatic Transmissions
Smooth and infinite variability: HSTs can provide smooth and infinite variability of speed and torque, which makes them ideal for applications where precise control of speed and torque is required.
Reversible: HSTs can be reversed instantly and smoothly, without the need for a separate reversing mechanism.
Compact and lightweight: HSTs are compact and lightweight, which makes them ideal for applications where space is limited.
High efficiency: HSTs are generally more efficient than mechanical transmissions, especially at low speeds.
Low maintenance: HSTs require relatively little maintenance, making them a cost-effective option in the long run.
Disadvantages of Hydrostatic Transmissions
Cost: HSTs are more expensive than mechanical transmissions.
Heat generation: HSTs can generate a significant amount of heat, which can reduce their efficiency and shorten their lifespan.
Noise: HSTs can be noisy, especially at high speeds.
Applications of Hydrostatic Transmissions
HSTs are used in a wide range of applications, including:
Industrial: HSTs are used in a variety of industrial applications, such as cranes, forklifts, and construction equipment.
Agricultural: HSTs are used in a variety of agricultural applications, such as tractors, combines, and hay balers.
Automotive: HSTs are used in a variety of automotive applications, such as hybrid vehicles and all-terrain vehicles (ATVs).
How Hydrostatic Transmissions Work
HSTs work by using a variable displacement pump to control the flow of hydraulic fluid to a variable displacement motor. The pump is connected to the prime mover, and the motor is connected to the driven load.
The displacement of the pump is varied by changing the angle of the swashplate. The swashplate is a rotating disk that is connected to the pump shaft. As the swashplate is rotated, the angle of the pistons in the pump changes, which changes the amount of fluid that is pumped.
The displacement of the motor is also varied by changing the angle of the swashplate. As the swashplate is rotated, the angle of the pistons in the motor changes, which changes the amount of fluid that is displaced.
The speed and torque of the driven load is controlled by the difference in displacement between the pump and the motor. When the pump displacement is greater than the motor displacement, the driven load will speed up. When the pump displacement is less than the motor displacement, the driven load will slow down.
Conclusion
HSTs offer a number of advantages over traditional mechanical transmissions, including smooth and infinite variability of speed and torque, reversibility, compactness, lightweight, high efficiency, and low maintenance. HSTs are used in a wide range of applications, including industrial, agricultural, and automotive applications.