Department of
Mechanical Engineering                                      
Department of Mechanical Engineering

Institute of Technology, Meghalaya                            National Institute
of Technology, Meghalaya

       Shillong, India

                      Bikash Kumar Sarkar                                                                         Subhendu Maity

Department of
Mechanical Engineering                                        Department
of Mechanical Engineering

Institute of Technology, Meghalaya                               National
Institute of Technology, Meghalaya

Shillong, India                                                                                
Shillong, India


Abstract­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ –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 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. This paper
present about different work has been done in the field of Hydrostatic
Transmission System.



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.



Transmission Systems







Open loop hydrostatic
transmission system:

Open 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 arrangement of open
loop hydraulic system is shown below:                                     

Fig.1 Open loop HST

In the above
open loop hydraulic system the electric motor or IC engine work as a prime
mover which drive the variable or fixed displacement hydraulic pump, the fluid
from the tank goes directly to the hydraulic motor which is controlled by
directional control valve and also from the output shaft of hydraulic motor is
connected to the load such as flywheel, propeller etc. The check valve and
pressure relief valve is used to control the direction 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.

Closed loop
hydrostatic transmission system:

Closed loop
hydrostatic transmission system is a system which that consists of two circuits
one is a main circuit and different one is charge or frame circuit.

In the main circuit a prime mover like
ic engine or motor, one bidirectional variable displacement hydraulic pump, one
bidirectional hydraulic motor, pressure relief valve, and two check valve to
deliver the fluid into the main circuit in lower pressure side and one pressure
relief valve. A pressure relief valve is used in this circuit for the safety purpose.
If the pressure in the output of the pump or input of the motor is greater than
or equal to the set pressure then the pressure relief valve open and all fluid
goes to the tank through relief valve to prevent the damaging of the motor,
main circuits and the charge circuit or make up circuit otherwise valve remain
closed as shown in the fig.


Fig.2 Closed
loop HST




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.


Fig.3 Torque for
low swash plate angle

Fig.4 Torque for
high swash plate angle

K. Dasgupta 2
has described the analysis of a hydrostatic transmission system using low speed
high torque motor. In this paper bond graph modelling approach has been used to
observe the dynamic of the machine. While modelling, the steady state solution
of the motor, considered as an input has been termed as quasi static solution.
Using system equation derived from the bond graph version, the steady state
behaviour of the system has been anticipated. 
Additionally the writer described approximately the theoretical and experimental
evaluation of quasi static in addition to constant state overall performance of
a hydrostatic transmission device along with a variable displacement axial
piston pump and an orbit motor has been mentioned.

Horst 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 had been extensively used in cell
machines and rancid-road vehicles. Within the industrial exercise the
transmission output torque, transmission ratio or output speed is normally
controlled through model unfastened PID control techniques. This techniques
effect in confined closed-loop bandwidth, limited running efficiency and
accuracy due to the excessive non-linear characteristic of the 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.

H. 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<1 min. Triet Hung Ho et al. 5 developed a modelling and simulation of hydrostatic transmission system with energy regeneration using hydraulic accumulator. This paper presents about closed loop hydrostatic transmission system energy saving system. The system improves the efficiency of the primary power source. The system is energy regenerative, highly efficient under partial load conditions. The accumulator is used in a unique way to recover the kinetic energy without reversion of fluid drift. Each variable displacement hydraulic pump/motors are used when the gadget operates within the go with the flow coupling configuration that allows enabling it to meet the hard requirement of some commercial and mobile applications. Also the round-trip performance of the system within the recovery testing varied from 32% to 66% when the losses of the load were taken into account. Hiren P. Patel et al. 6 Explained about the hydrostatic continuous variable power transmission drive for two wheeler using radial piston pump and motor set. In vehicle power transmission is a prime source of electricity losses. The continuous variable strength transmission gadget is a device that makes it feasible to vary step by step the transmission ratio. Consequently it lets in choice of an infinite wide variety of transmission ratios between driving and driven shaft. It is able to be revealed that the hydrostatic non-stop variable transmissions are very common in heavy responsibility off motorway automobiles and machine however no longer famous for on dual carriage way automobiles. Those are certain efforts inside the direction of hydrostatic nonstop variable transmission utility in small motors. However nevertheless none had used radial piston pump for that. So some studies work may be one inside the path of the usage of radial piston pump and motor set for designing of hydrostatic non-stop variable transmission for small ability automobiles.  Somashekhar S. Hiremath et al. 7 discussed about the optimization of process parameters in series hydraulic hybrid system through multi- objective function. This paper describes the assessment between electric and hydraulic vehicles such as truck, cars etc. IN the present day the gas-electric powered hybrid and hydraulic hybrid systems are considerably more energy and fuel green than conventional cars. Power of electrical hybrids is its high power density of electric batteries, allowing for massive garage in especially compact and light-weight batteries. Hydraulic hybrid is the capability technological answer for the limitations in the electric powered hybrid vehicles. The dynamic reaction of the device is studied the usage of simulation effects of the system version in AMESim tool. G.K. Gangwar et al. 8 proposed the study of closed- circuit hydraulic energy- regenerative system for hydrostatic transmission drive using hydraulic accumulator. The layout of closed loop hydraulic energy regenerative system for hydrostatic transmission drive applying hydraulic accumulator and its modelling is given in briefs. The accumulator is used for the safety cause and to get better the kinetic power without the reversion of fluid go with the flow. This paper present the creation, mathematical modelling and assessment of the engineering and mechanics of all the components used inside the evolved hydraulic system. The experimental results indicated that the designed device changed into powerful and that the spherical trip recovery efficiency varied from 22% to 59% for the take a look at a bench. S.M. Limon et al., 9 proposed the hydrostatic transmission failure analysis and utilization of failure knowledge. This paper discussed approximately comprehensive failure expertise is necessary to hold and improve this vital gadget, a scientific failure evaluation of the hydrostatic machine is presented in this work, which maps failure mechanisms and root reasons of failure into suitable physics of failure  fashions of most crucible components. Hydrostatic transmission system is a completely critical sub-gadget of production device and sudden disasters to those systems may motive major disruptions in normal operation. Hongyan Yang et al. 10 discussed about the comparative study on PID control and fuzzy control of motor speed of hydraulic transmission type wind turbine. Research indicates that the constant displacement pump–double variable displacement motors speed regulating gadget can make the everlasting magnet synchronous generator velocity balance. The impact of Fuzzy manage is better than that of the PID control. In this paper, it is miles put forward to apply variable displacement vehicles riding permanent magnet synchronous generator. Dynamic model considering the effect of long hydraulic pipeline can clearly mirror the transient stabilization manner of the hydraulic pressure type wind electricity technology device, While the velocity increases, the output speed of the constant displacement pump increases, as the output drift of the pump will increases and the input waft of the motors will increase, variable displacement motors routinely alter the displacement and the speed of the motor output shaft keeps steady. The requirement of pace manage is met as synchronous generator includes into the energy grid. The author additionally mentioned approximately the PID manage and fuzzy control that is higher dynamic response than the PID manipulate.    Fig.5 Fuzzy control motor output speed .      III.     SYSTEM MODELLING The modelling of hydraulic motor, hydraulic pump and accumulator is given by 3 Hydraulic motor: The volumetric efficiency, mechanical efficiency, actual flow rate and actual torque of the hydraulic motor are expressed by the equation from (1) to (4) respectively: .............................. (1)   ............................. (2)   ................................................ (3)   ................................ (4)   Hydraulic pump: The volumetric efficiency, mechanical efficiency, ideal flow rate and ideal torque of the hydraulic pump are expressed by the following equations from (5) to (8) respectively: .............................. (5)   ......................... (6)   ......................................... (7)   .................................... (8)   Accumulator: An accumulator is an energy storage device. It stores potential energy through the compression of dry inert gas in a container open to a relatively incompressible fluid. The hydraulic accumulator here is modelled based on its physical attributes. The van der waals'equation is employed to model the hydraulic accumulator. The compression of an accumulator is considered as isothermal process     (and expansion is assumed to be adiabatic process (. The gas pressure in the accumulator is expressed by the following equation (9) ................. (9) The energy stored in the hydraulic accumulator is estimated by the equation (10) ....................................... (10) IV.    SIMULATION AND RESULTS The following experimental, simulation curve shows the validation of the hydrostatic transmission system by doing a number of literature reviews  Fig. 6 Modelling of Hydraulic Motor in Simulink Fig. 7 Overall efficiency vs Pressure (bar)   Fig. shows the overall efficiency versus the operating pressure of the motor. The maximum efficiency was about 0.94 at a pressure of 200 bar and ?= 1. The minimum efficiency was about 0.68 at a pressure of 50 bar and ?= 0.25. At a given operating pressure, the overall efficiency increased in correspondence to the value of ?. For example, at a pressure of 50 bars, the value of the overall efficiency increased from 0.68 to 0.87 as ? increased from 0.25 to 1.   Fig. 8 Overall efficiency vs Motor speed (RPM)   V.      CONCLUSION In this paper the basic concept of hydrostatic transmission system and also about the closed loop and open loop hydrostatic transmission system is discussed. In this it shows that the improvement in efficiency by using hydraulic accumulator is discussed. An accumulator is an energy storage device it stores potential energy. Matlab simulink software is used to develop the mathematical modelling of the system. The overall efficiency of the system varies proportional to motor speed in a given displacement ratio. Comparing the theoretical and therefore the experimental responses of the system, it is going to be over that the model fairly represents the behaviour of the system.   VI.      REFERENCES 1 N.D. Manring, and Greg R. Luecke, "Modelling and designing a Hydrostatic Transmission With a fixed-Displacement Motor," vol. 120, pp. 45-49, March 1998. 2 K. Dasgupta "analysis of a hydrostatic transmission system using low speed high torque motor," in Mechanism and Machine Theory, Vol. 35, pp. 1481-1499, June 1999. 3 Horst Schulte, "Control-oriented modeling of Hydrostatic Transmissions considering leakage losses," Bosch Rexroth AG, proceedings of The International Federation of Accountants, vol. 40, pp. 103-108, 2007. 4 H. Rahrovan and H. Gholizade "Energy Recovery in Hydrostatic Transmission Systems using Accumulator" Fluid Power Laboratory Islamic Azad University of Qazvin, 2008. 5 Triet Hung HO, and Kyoung Kwan AHN "Modelling and simulation of hydrostatic transmission system with energy regeneration using hydraulic accumulator," Journal of Mechanical Science and Technology, vol. 24, pp. 1163-1175, March 2010. 6 Hiren P. Patel, Vijay K. Patel, and V. R. Bhatt, "Hydrostatic continuous variable power Transmission drive for two wheeler using radial piston pump and motor set," International Journal for Scientific Research & Development, vol. 1, pp. 710-715, March 2013. 7 Someshekhar S. Hiremath, R. Ramakrishnan and M. Singaperumal "optimization of process parameters in series hydraulic hybrid system through multi- objective function" The 13th Scandinavian International Conference on Fluid Power, SICFP2013, pp. 199-205, June 2013. 8 G.K. Gangwar, Madhulika Tiwari, and Bipin Kumar Singh, "study of closed- circuit hydraulic energy- regenerative system for hydrostatic transmission drive using hydraulic accumulator," International journal of research in aeronautical and mechanical engineering, vol. 2, pp. 1-10, Jan 2014. 9 S. M. Limon, O. P. Yadav, J. Muscha , and  B. Nepal "Hydrostatic Transmission System Failure Analysis and Utilization of Failure knowledge," in International Engineering and Engineering Management, pp. 981-985, Jan 2016.    10 Hongyan Yang, and Gejin Hu "Comparative Study on PID Control and Fuzzy Control of Motor Speed of Hydraulic Transmission Type Wind Turbine," IEEE International Conference on Power and Renewable Energy, pp. 399-403, Oct 2016.   .            


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