Systems of Hydraulic Drives - Dynamics of Hydraulic Drives of Winch and Mechanism of Lifting-lowering
of Boom of Building Self-propelled Cranes
Dynamics of hydraulic drives of the main winch and the mechanism of lifting-lowering
Hydraulic systems of building self-propelled cranes differ homogeneous structure; therefore at their creation methods of block-modular logical
synthesis  are often used. However in some cases for design of systems of hydraulic drives only formal logical methods may be insufficient;
the additional assessment of working capacity of system and definition of its main parameters connected with adjustment of hydraulic devices and
a specific character of their work is often necessary. The approached calculation by development of hydraulic systems of cranes is interfaced to
a number of assumptions and impossibility of the account of variation of many factors in time, especially at dynamic calculation that leads to that
adjusting parameters of hydraulic system appear, as a rule, overestimated. In order to prevent unreasonable losses of capacity of a drive of the
crane, especially in modes of lowering of a cargo and a boom, these parameters specify at debugging hydraulic system individually for each crane at
its test in a plant. However, at enough limited resources of appropriating manufactures the experimental choice of parameters of adjustment also
does not guarantee achievement of their optimum values.
of boom of building self-propelled cranes carrying capacity 25 and 100 tons
In conditions of a plenty of models of cranes and a wide range of loads the decision of such problem is essentially facilitated by application of
software of the computer-aided analysis. In particular, by means of the program HYDRA researches of dynamics of hydraulic systems of the main rise
winch and the mechanism of a boom slope for cranes by carrying capacity 25 and 100 tons have been carried out. These mechanisms in modes of lowering
of cargoes, a boom at wrong adjustment of brake and pressure relief valves are subject to self-oscillations. Therefore objective of the executed
researches was definition of values of some the parameters providing smooth running of mechanisms in specified modes, as well as an assessment of
their influence on stability of work, character of transients in a hydraulic drive, peak pressures.
On Fig. 1, a, b, rated diagrams of hydraulic systems of cranes are resulted: a hydraulic drive of the cargo winch (a)
and a hydraulic drive of the mechanism of a boom slope (b) with the nodes 1, ... , 31 put on them. Each typical hydraulic element (the
pump, the hydraulic motor, the valve, etc.) is described by the certain mathematical model reflecting its basic dynamic properties. For the
direct operation pressure relief valve connecting nodes 15 and 16, the simplified mathematical model, described only static characteristic has been
used within the limits of the considered problem. The brake valve is presented on the rated diagram in the form of a combination of the
spring-loaded piston of a regulator and an adjustable throttle which through passage section is function of the piston movement.
As the basic revolting influences have been accepted: forces, moments, reduced weights, a movement of the hydraulic control valve spool.
Moment on the winch drum shaft in view of a dynamic load  is:
Dd – diameter of a drum; mc – mass of a cargo; Kp - an multiplicity of a polyspast;
ηp – an efficiency of a polyspast; ω – a frequency of own fluctuations of mechanical system of the crane and a cargo;
nhm – a frequency of rotation of the hydraulic motor shaft; uw – a transfer number of the winch gear;
g – a free fall acceleration.
Dependences of the boom mass with a cargo mred and forces Rc, reduced to a rod of the hydraulic cylinder
of the boom lifting-lowering mechanism, of the relative stroke of the piston S / Smax where Smax –
the maximal stroke of the piston, are presented on Fig. 1, c, d.
Movement of the hydraulic control valve spool from one position to another was carried out of linear law for 1 s.
During modeling hydraulic systems a stability of modes of lowering of the crane mechanisms was checked at various adjustment pressures
pb of the brake valve (pressure of the beginning of opening of a stop-adjustable spool) which changed from 2 up to 5 MPa.
The dynamic analysis of hydraulic systems of the cargo winch and the boom slope mechanism, for example, for the crane carrying capacity 100 t, was
spent at the following values of main parameters: geometric volumes of the pump and two hydraulic motors of 225 cm3/rev; diameters of
the hydraulic cylinder piston and rod of 300 mm and 200 mm, a stroke of the piston of 2980 mm; diameter and length of pressure and drain pipes
according to 32 mm and 2 m; the adjustment pressure of the pressure relief valve pprv = 17.5 MPa; an angular speed of the
pump shaft 100 rad/s; the working liquid elasticity volumetric module of 1000 MPa; the maximal area of through passage section of an adjustable
throttle 9-10 was equal 2.4 cm2; a nominal bore diameter and a stroke of the hydraulic control valve spool are equal according to 32 mm
and 24 mm.
In cranes of more carrying capacities the increase of quantity of hydraulic engines was considered by respective alteration of parameters of the
hydraulic cylinder or the hydraulic motor.
The analysis of the received results has shown that the most sensitive to variation of parameters of adjustment is the mechanism of load-lifting
winch. Fluctuations at transients in hydraulic systems of winches for cranes of all considered capacities begin at values pb
in 1.5 times greater, than in hydraulic systems of the boom lifting-lowering. Fig. 2, a shows the dependencies , with the help of
which it is recommended to choose the adjustment pressure of the pressure relief and brake valve for mechanisms of winch and the boom
On Fig. 2, b, c, d the typical rated oscillograms of transients in hydraulic systems of mechanisms of the cargo winch
and the boom lifting-lowering for the crane by carrying capacity 100 t in a mode of lowering are resulted at pb = 3.5 MPa.
As can be seen from Fig. 2, b stabilization of the boom lowering speed v12 occurs more quickly (0.7 s), than
stabilization of frequency of the hydraulic motor shaft rotation n12 (1.1 s) which has thus rather amplitude and smaller
frequency of fluctuations. Fluctuations of pressures (Fig. 2, c) in bringing and allocating pipe lines of the hydraulic motor
p22, p23m and the hydraulic cylinder p24, p23c
have identical frequency, but differ on amplitude and a phase. Attenuation of fluctuations of these sizes up to the established values of amplitude
in the winch mechanism occurs through 1.1 s after the beginning of switching of a spool. Fluctuations of pressures in the hydraulic cylinder occur
with small amplitude and low frequency that testifies to smaller susceptibility of hydraulic system of the boom lifting-lowering mechanism to
Dynamics of movements x14m and x14c of the brake valve spool at work of winch and the
boom slope mechanism in the hydraulic system, as well as the law of movement of the hydraulic control valve spool х are shown on Fig. 2,
The analysis of oscillograms has shown, that hydraulic systems possess a sufficient degree of damping of elements for clearing own fluctuations.
The adjustment pressure of the pressure relief valve pprv, limiting the pressure developed by the pump during lowering of a
cargo and a boom has been established, that, does not render influence on stability of these processes. However, for prevention of unjustified
losses of energy by the basic condition for a choice of size pprv there should be maintenance of nominal speed of lowering.
By calculations it has been established, that lowering of mechanisms begins only at compliance with a condition
pprv / pb > 1 as only thus opening the brake valve begins. Achievement of nominal speed of lowering at
completely open channel of the hydraulic control valve is probably only at fulfillment of the condition
pprv / pb ≥ 1.2.
In view of the static characteristic of the pressure relief valve the stock on pressure for maintenance of its stable work together with the brake
valve has been accepted.
The received rated results have been checked experimentally up at stands, as well as on cranes by carrying capacity 25 and 40 t . The transients
received by experiment, have the same character, as rated ones, and their parameters differ no more than on 5-8 % that testifies to a sufficient
correctness of the executed numerical analysis.
On the basis of the fulfilled researches basic diagrams of hydraulic systems of the cranes have been updated, the level of adjustment pressure of
the pressure relief and brake valves is proved and lowered; dynamic characteristics of hydraulic systems are improved.