Commercial Vehicle Transmission System - Hydrostatic Transmission

 What is Hydrostatic Transmission?

Transmission of power using interconnected devices from one point to another is called power transmission. Mechanical, electric, hydrodynamic, hydromechanical, and hydrostatic transmission are some categories of power transmission. This article included the topic hydrostatic transmission. But, a few details regarding other power transmission methods are also listed below.

Mechanical Transmission: These type of transmission system uses shafts, gears, torque converters, chains and belts for converting mechanical energy to kinetic energy.Transmission of power from an engine to the wheels of an automotive is an application.

Electric Transmission: In Electric transmission, an electric generator is used for converting mechanical energy to electric and with an electric motor this is converted back to mechanical energy. Electric transmission occurs in transformers.

Electric Transmission: In Electric transmission, an electric generator is used for converting mechanical energy to electric and with an electric motor this is converted back to mechanical energy. Electric transmission occurs in transformers.

Hydromechanical Transmission: A hydromechanical transmission uses a power split scheme for improving the efficiency of gearboxes and for providing flexibility. This transmission method converts the input energy to both mechanical and hydrostatic energy and is suitable for heavy duty applications.

 Hydrostatic Transmission

Now, we can move on to hydrostatic transmission.What is a hydrostatic transmission?

• Simply, it is a hydraulic system where the hydraulic pump or an accumulator will drive the motor using the fluid passing through flexible hoses.

• In hydrostatic transmission, gears are not required for converting rotating mechanical energy from one source to another.

• Because, when the displacement of pump and motor are fixed, then hydrostatic transmission itself will act as a gearbox.

• Hydrostatic transmission is suitable for applications that require variable output velocity or torque.

• Some of these applications include golf course maintenance equipment, harvesters, tractors, trenchers, agricultural and large construction equipment

The advantages of the hydrostatic transmission system 

-With a constant input speed, hydrostatic transmission can deliver variable output speed and vice versa.

-In a minimum time period, reverse direction of output

-Rotation is possible.

-Adjustment of speed, power and torque is possible with hydrostatic transmission.

-Smooth and controlled acceleration. 

-Fast response and Precise speed under variable load.

-Hydrostatic transmission can be stalled without

-Damage or overheating and Ease of control.

-Provide dynamic braking.

-Hydrostatic transmission can transfer power from one prime mover to different locations and compact size.

 The Principles Behind Hydraulic Power:

To understand how a Hydrostatic Transmission works we need to first understand the basic characteristics of liquids:

i.Liquids cannot be compressed

ii.Liquids have no shape

iii.Liquids transmit pressure in all directions and have equal force to all perpendicular surfaces

The hydrostatic transmission moves oil in a closed circuit to rotate a motor in both directions. Because liquids have no shape we can manipulate and route it easily. Since they cannot be compressed and transmit equal force to all perpendicular surfaces, we can use it to multiply input force and transform it into a greater output force.The speed of your transmission’s output is dependent on the rate of volume the oil is flowing. This is measured in gallons per minute (GPM).

The direction of your transmission’s output is dependent on which direction the oil is being pumped. The power of your transmission’s output is dependent on the oil’s pressure. So the faster the oil is pumped from one side of the transmission to the other, the faster your tractor moves,and the higher the pressure, the stronger it turns.

Hydrostatic Transmission Components

The components required for a hydrostatic transmission system are :

a)Transmission case (to hold components in place and for fluid transfer)

b)A charge pump (for providing initial case oil pressure and to fill circuit with oil)

c)The input shaft (to take power from the engine and to rotate the charge pump)

d)Axial piston pump (rotates the input shaft and to pump oil to the motor)

e)Hoses / passageway (to connect pump to the motor),

f)Pressure relief valves (provide alternative path for oil when pressure increases),

g)Motor (drives the output shaft),

h)Swash plate (changes the displacement of the piston pump),

i)Check valve (used in closed loop circuit).

Hydrostatic Operation

a)Hydrostatic transmissions are a pump and motor connected in a circuit together

b)Most are constructed using piston pumps and piston motors

Four basic configurations:

a)In line

b)U shaped

c)S shaped

d)Split

In Line Configuration

i)The pump is directly connected to the motor

ii)All fluid is contained within the pump/motor combination

iii)Usually uses a variable pump and a constant displacement motor

U Shaped Configuration

i)Similar to the in line except that the motor is connected under the pump.

ii)The motor shaft goes out the same direction and the input shaft.

iii)Used when the drive axle is under or behind the prime mover.

S Shaped Configuration

i)Similar to the U shaped configuration.

ii)The motor shaft goes out behind the prime mover, but under it.

iii)Used when the drive axle is under the level of the prime mover.

Split Configuration

i)The motor and pump and motor are not physically connected together.

ii)The motor can be located some distance from the pump and across a barrier.

iii)Contains very high pressure hose that connects the pump to the motor.

How Does a Hydrostatic Transmission Work?

Every hydraulic system, as we all know, requires hydraulic fluids, which are kept in a reservoir. When the engine runs in a hydrostatic transmission system, it rotates the drive shaft and the input shaft is attached to it. The movement of this input shaft in a closed circuit system will turn both the charge pump and the piston pump. As a result, the charge pump will draw oil from the reservoir and transfer it to the transmission case. The oil will pass through the hoses and towards the motor due to the reciprocating motion of the piston caused by a change in the angle of a swash plate.

Power transmission route of hydrostatic transmission wheeled vehicle

Hydrostatic Transmission Operation Pump

- The cylinder is turned by the input shaft.

- The pistons are connected to a swash plate, which varies how much the pistons travel.

- The greater the angle of the swash plate, the more fluid is pumped.

- Reversing the angle of the swash plate causes it to pump backwards.

- The more fluid is pumped per revolution, the more horsepower is needed.

Hydrostatic Transmission Operation Motor

a)The motor accepts the fluid from the pump and turns a differential or wheel, depending on the configuration.

b)When the pump reverses direction, the motor turns backwards, giving you reverse. 

c)Not all hydrostats are designed to pump backwards.

d)Many motors use a shuttle valve to reverse the flow of hydraulic fluid.

Hydrostatic Circuits Open circuit

•All fluid comes from the tank and is pumped to the motor.

•When the fluid leaves the motor, it goes back to the tank.

•Does not require a charge pump.

Hydrostatic Circuits Closed circuit

•The fluid is pumped to the motor.

•As the fluid leaves the motor, it is returned to the pump inlet.

•Requires a charge pump.

Conclusion

It is easier to design a sprayer with a hydraulic motor drive. The hydraulic drive motor makes it easy to build a track-adjustable axle, and the dropper can be made long or short as needed. It is hoped that some knowledge and information about the commercial vehicle system that is Hydrostatic Transmission can provide knowledge and benefit to all of us who read my blog. Happy reading.