Abstract­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ the fixed and variable displacement pumps

–This paper present a review of the Hydrostatic Transmission System (HST). A
Hydrostatic transmission system is a system within which the energy of the
input drive shaft is reborn into pressure energy so reconverted into energy at
the output of the shaft. The review divides the classification of hydrostatic
transmission systems, application in automobiles, wind turbines and also
discussed about the fixed and variable displacement pumps and motors which are
used in Hydrostatic transmission system. In closed loop hydrostatic
transmission system the pump has to be able to supply a proportional oil flow
to the hydraulic motors. The need for huge energy transmissions in tight space
and their control with incredibly rapid feedback for army, commercial
application as well as in modern applications require motors with very
excessive ‘torque to inertia’ ratio. The simulation work is carried out in
Matlab simulink. This paper present about different work has been done in the
field of Hydrostatic Transmission System.

Transmission System; Classifications; Wind Turbines; Fixed Displacement
hydraulic pumps; Motors; Applications; Matlab simulink. 

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The increasing
demand for power transmission systems in military, industrial and modern
applications (such as automatic transmission in vehicles, robotics etc) which require
hydraulic motors with high power to weight ratio. The essential function of
Hydrostatic transmission system is to accept energy from input then transmit
and regulate the energy within the HTS and deliver an energy to the output load
which is connected to hydraulic motor. The pump is connected directly to the motor.
The pump may be fixed or variable depending upon the applications. If the pump
is variable displacement then it is easy to adjust the output speed of the
motor in order to get the desired output speed or torque from the motor because
power depends on torque and rotational speed. Then it is feasible to regulate
the speed ratio in between pump and motor. Hydrostatic transmission system
mainly consists of two parts one is open loop HST and other one is closed loop
HST i.e.







1 Classification of HST System

Open loop HST system:

loop HST is a system in which pump is not directly connected to the hydraulic
motor. It mainly consists of reservoir, filter, and pressure relief valve
(PRV), fixed or variable displacement hydraulic pump or motors. The simple circuit
diagram of the open loop hydraulic mechanism is shown below:                                     

Fig.2 Open loop HST

shown above in open loop hydraulic system the electric motor or IC engine work
as a main mover that drive the fixed or variable displacement hydraulic pump,
the fluid from the tank flows to the hydraulic motor that is controlled by directional
control valve and additionally from the output shaft of hydraulic motor is
connected to the load like such as flywheel, propeller, mechanical devices etc.
The check valve and pressure reducing valve control the order of flow and in
the hydraulic circuit and the pressure relief valve is use mainly for the
safety purpose when the pressure in the circuit exceeds the maximum set value
then the fluid back comes to the reservoir. The pressure control valves are
used to limit the pressure in the circuit up to a certain level.

loop HST system:

loop HST consists of two circuits one may be a main circuit and the other one
is frame circuit.

In main circuit primary
mover like IC engine or motor, one duplex variable displacement hydraulic pump,
one bidirectional hydraulic motor, pressure reducing valve, and  check valve to deliver the fluid into the main
circuit in lower pressure side and one pressure relief valve. A pressure
reducing valve used in this circuit for safety purpose to avoid damaging of the
circuit. If the pressure within the output of the pump or input of the motor is
larger than the set pressure then the pressure reducing valve opens and the fluid
flows to the reservoir through reducing or safety valve to stop the exploding of
the motor, main circuits and therefore the charge circuit or structure circuit
otherwise valve stay closed as shown within the fig.



Fig.3 Closed
loop HST


Model of wind turbine using HST system

the given fig. 4 it shows that hydrostatic transmission system is used in wind
turbine which consists of radial piston pump, axial piston pump and generator.
The high pressure line and low pressure line are connected to axial piston
motor and radial piston pump respectively.

Fig. 4
Hydrostatic transmission system in wind turbine




N.D. Manring
et al. 1 discussed about the modelling and designing of a Hydrostatic
transmission with a fixed-displacement motor. In this paper the dynamic
equation of the variable displacement axial piston pump with fixed displacement
motor is done. The given system consists of motor, the pressurised hose, and
the pump which when combined leads to the third order system. The stability of
the system is presented by Routh-Hurwitz criterion and also the advantages and
disadvantages of the hydrostatic transmission system are discussed. The author
develops the dynamic model of a hydrostatic transmission system. Based upon the
second-order approximation the characteristic equation, the effect of
particular design variations on the system rise-time, settling time and maximum
percent overshoot has been discussed. Finally this study has provided greater
intuition into the behaviour of a hydrostatic transmission.

Dasgupta 2 has described the analysis of a hydrostatic transmission system
using low speed and high torque motor. To observe the dynamic of the machine, bond
graph modelling approach has been used. Applying system equation derived from
the bond graph version, the steady state behaviour of the system had
anticipated.  Additionally the writer
described approximately the theoretically and practically evaluation of quasi
static in overall performance of the hydrostatic transmission system with the
used of the variable displacement pump and an orbit motor has been mentioned.

Sanada 3 discussed about the study on a full-electric control system of a
hydrostatic transmission for construction machines. He discussed about the
behaviour of a swash plate pump for the experiment. In this two DOF is used for
the controlling of the motor speed. AMESim software is used for simulation.

Schulte 3 have been discussed about the control-oriented modelling of
hydrostatic transmissions considering leakage losses. Hydrostatic transmissions
machine also referred to as hydrostatic gears which are extensively recycled in
cell machines, rancid-road vehicles. Within the industrial exercise the transmission
is normally controlled through model unfastened PID techniques. This techniques
impact in confined closed-loop information measure restricted running potency
and accuracy due to the excessive non-linear unique of plant. Additionally the
author mentioned about the manipulate oriented model of a standard hydrostatic
transmission as a primary step closer to a multivariable version-primarily
based fuzzy country feedback benefit scheduling controller based on parallel
allotted repayment scheme the use of Takagi-Sugeno fuzzy systems. A further
paper will gift a fuzzy country comments gain scheduling controller concept the
use of derived Takagi-Sugeno fuzzy model of the plant.

Rahrovan et al. 4 developed the energy recovery in hydrostatic transmission
systems using accumulator. In this paper the proposed hydrostatic machine that
is capable of keep power as much as 50% and extra in evaluate to conventional
hydrostatic systems. The usage of the prefect accumulator, electricity loss
through thermal dissipation is reduced, ranging performance rates reduced to
0.95 in cycle times of t

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