Dynamic expressanalysis of hydraulic systems  Typical structures of hydraulic circuits
Typical structures of hydraulic circuits and their description
The decision of the problem is based on representation of structure of the hydraulic circuit in the form of set of separate components – functional blocks of which practically any hydraulic circuit (Fig. 1) usually consists. There are: a diesel engine, pump station of open type (with an opened flow circulation), pump station of closed type (with a closed flow circulation), hydraulic actuators (hydraulic motor, two in parallel connected hydraulic motors, hydraulic cylinder, two in parallel connected hydraulic cylinders), various kinds of loading (elasticinertial of forward or rotary action, wheel carrier), machine (block of simulation of progressive machine motion at tractivedynamic calculations). Each of listed functional blocks is described by system of mixed differential and algebraic equations.
Fig.1. Functional blocks of hydraulic systems.
a – diesel engine with centrifugal regulator; pump stations: b – with opened flow circulation, c – with closed flow circulation; hydraulic actuators: d – single hydraulic motor, e – two in parallel connected hydraulic motors, f – single hydraulic cylinder, g – two in parallel connected hydraulic cylinders; elasticinertial loading: h – of forward action, i – of rotary action; j – wheel carrier, k – machine
In a basis of the structural description of the hydraulic circuit an identification of functional blocks and representation lays, that each of them has no more than four nodes (points) in which it incorporates to other blocks of the circuit (Fig.1). The binding of nodes and identification of functional blocks are carried out as follows (tab. 1):
Table 1. Classification of functional blocks of hydraulic systems
Functional block 
Block identifier 
Node i 
Node j 
Node k 
Node l 
Diesel engine 
DIESEL 
 
 
Engine shaft 
Regulator muff 
Pump station
with opened flow
circulation 
OPENED

Pressure head line^{*)} 
Drain
line^{ *)} 
Pump shaft

 
Pump station
with closed flow
circulation 
CLOSED

Pressure head line 
Drain
line 
Shaft of basic
and boost pump 
 
Hydraulic motor

MOTOR1 
Pressure head line 
Drain
line 
Hydraulic motor shaft 
 
Two in parallel
connected hydraulic
motors 
MOTOR2

Pressure head line 
Drain
line 
Hydraulic motor shaft 
Hydraulic motor shaft 
Hydraulic cylinder 
CYLINDER1

Pressure head line 
Drain
line 
Hydraulic cylinder rod 
 
Two in parallel
connected hydraulic
cylinders 
CYLINDER2

Pressure head line 
Drain
line 
Hydraulic cylinder rod 
Hydraulic cylinder rod 
Elasticinertial
loading 
LOADING

 
 
Moving mass 
Hydraulic motor shaft or hydraulic cylinder rod 
Wheel carrier 
WHEEL

Wheel axis

Contact
point of
wheel with
road 
Machine case

 
Machine

MACHINE

Machine case 
 
 
 
^{ }
^{*) }Hereinafter pressure head and drain lines are defined by accepted direction of flow of a working liquid. At change of a direction of flow when pressure head and drain lines vary places, there is a change of signs on corresponding flows of liquid, a binding of nodes i and j thus remains constant.
By preparation of the hydraulic circuit for calculation its nodes are numbered in the arbitrary order then the structure of the circuit is described by a matrix which line looks like:
where Т – functional block identifier; n – number of the given type block;numbers of block nodes.
The functional block identifier serves for a choice from the library of mathematical models the system of equations corresponding given type of the block. The variables entering into the equations of the block both describing its input and an output, are indexed under numbers of nodes of the given block.
