Note: Descriptions are shown in the official language in which they were submitted.
2161619
-2-
The invention relates to an invention for preheating hydraulic circuits,
including the drive systems, in order to guarantee functional and op~,aLiolldl
reliability. It is particularly suitable for the operation of hydraulic systems at low
ambient temperatures, such as the operation of conveying equipment in cold
5 regions.
It is a known fact that at low ambient temperatures hydraulic systems
can be got ready for operation by preheating the fluid reservoir or the hydraulic
lines and by flushing hydraulic oil through the lines without the .~ tiol1 of
pressure. For example, German Patent 268 044 describes a procedure and a
10 device for heating or cooling hydraulic lines; according to this procedure the
system is preheated by heating up a section of the hydraulic lines by circulating
hot air in a twin-chamber passageway. In this procedure, the hydraulic fluid is
pumped around the system of hoses and tubing and is maintained at operating
temperature. Intheilllllledià~vicinityoftheoperatingelement,e.g. ahydraulic
15 cylinder, a connecting line fitted with a short-circuit valve through which the
hydraulic oil flows back is provided between the feed line and the return line.
In order to exclude the possibility of the operating element being
influenced in an uncontrolled manner, the supply and return lines are each
separated from the operating element by a shut-off valve. In this way, the
20 hydraulic fluid in the operating element is excluded from the heating circuit. If
the ~perating element is then actuated, heated hydraulic fluid flows into the
cold operating element and this leads to operational disturbances or increased
wear. In extreme cases even a thermal shock, which is the most critical of all
stresses, may occur. The functional disturbances caused in this manner do not
25 disappear again until these equipment elements have become thoroughly
warmed up.
Operating elements which are operated relatively rarely and then only for
short periods of time, are for the most part exposed to unfavourable operating
conditions because at low ambient temperatures the operating elements arc
30 rarely if at all thoroughly heated.
, . , _ _ _ _ .. .. . _ . _
21 6 1 6 1 9
-3-
The object of the invention is therefore to avoid these disadvantages.
According to the invention, an arrangement is provided for preheating
hydraulic circuits in conveying machinery used in low-temperature
environments. The purpose is to guarantee operational reliability by flushing out
5 the pipelines by circulating the oil in a non-pressurized state and by providing
preheating of the oil reservoirs. In accordance with the invention, the hydraulic
cylinder or hydraulic cylinders are included in the preheating circuit and for this
purpose an additional transfer pas:,agc~ c~y is provided in the lifting piston rod.
This creates an additional Co11, ,eu~iul~ between the piston space and the system
10 of hydraulic lines. By means of the valves provided for the purpose, special
circuits can be brought into operation to permit the non-pressurized circulationof the oil as well as to retract and extend the piston rod.
The specific hydraulic circuits for the three states provide
- non-pressurized circulation
- retracting piston rod and
- extending piston rod.
The advantage of the invention is that when conveying machinery and
other equipment is used in cold environments, the entire hydraulic system can
be preheated to guarantee operational reliability and reduced wear, and as a
20 result normal operating conditions can be ,,,c,;,,L.. .,ed at all times.
An embodiment of the invention is illustrated in the drawing and
described in more detail below. The drawing shows
Fig. 1: AdidyldlllllldLiuviewofaheight-~ llct~hleboomforaconveying
system, and5 Fig. 2: The circuit diagram for a simple hydraulic lifting device according
to Fig. 1.
Fig. 1 depicts a boom 1 of the kind used as a discharge boom on an
excavator, spreader or similar. This boom 1 can be pivoted horizontally by a
2161619
-4-
drive mechanism which is not further described here and it can be pivoted
vertically by the hydraulic cylinder 2. In the process, a tensile load is applied
to the hydraulic cylinder 2.
The designations used for the individual operating elements depicted in5 the circuit diagram for the simple hydraulic lifting device according to Fig. 2 are
the desiy"alions p,t:s.,,iL,ed for such circuits and they reveal the operating
principle of the circuit to any expert familiar with this field. Consequently, it is
unnecessary to provide any further detailed descriptions of these operating
elements and their method of operation.
One special feature that should be mentioned is that the pressure-limiting
valve VD1 is used to protect the circuit against any ~""~ell"i~l~d excess
pressure, the filter F with bypass VR3 is used to purify the returning fluid 3,
and the flow control valve VDr1 is used to limit the lowering rate.
It is furthermore especially important that the piston rod 4 of the
15 hydraulic cylinder 2, which bears the customary designation MY1 in the circuit
diagram shown in Fig . 2, possesses a passag~ ~r. dy (also referred to as
"additional transfer" passag~u;) 6 running in the longitudinal direction.
In the unpressurized circulation mode, the pump P1 pumps oil 3 from
the tank T through the ' ~-;Lio,1c,l control valve VW1; P-->A through
20 passageway 6 in the piston rod 4 of the hydraulic cylinder MY1 and into the
piston space 5 of the cylinder. In the process, the check valve VR2 is forced
open. The oil 3 emerging at connection point A on the hydraulic cylinder MY1
flows back into tank T via the directional control valve VW2; AB-- > T, which
is in its open middle setting.
In this constellation, the pre-heated hydraulic oil 3 gives off heat to the
working cylinder MY1. In addition, the opening pressure of the check valve
VR2 generates an additional temperature increase which has a positive effect
on the overall operation.
. ` 2161619
-5-
The lower function is controlled by directional control valve VW2.
In this case, the solenoid a in ' ~iLiol-al control valve VW1 is energized
and the passageway P-->A; B--~T is established. At the same time, the
energized solenoid a in directional control valve VW1; P--> I blocks the
5 unpressurized circulation of the oil.
The oil 3 leaving directional control valve VW2 flows into the piston
space 5, which is now sealed off by the check valve VR2. As the pressure
builds up, it open up the holding valve VR1 via the pressure-limiting valve VD2.The oil 3 leaving on the differential side of the hydraulic cylinder MY1 is able10 to flow back into the tank T via the passag~wdy connection in the directional control valve VW2; B-->T. The hydraulic cylinder MY1 is extended.
When the solenoids a of d;,el,Lional control valves VW1 and VW 2 are
switched off, the process comes to an end. The control pressure drops up via
the flow control valve VDr2 and the holding valve VR1 locks the hydraulic
15 cylinder MY1.
The raise function is controlled via ' t:-,Lio,1cl1 control valve VW2.
In this case, the solenoid b of directional control valve VW1 is energized
and the passageway P~>B, A-->T is established. At the same time, the
energized solenoid a of the directional control valve VW1; P-- I, T-- I blocks the
20 unpressurized circulation of the oil.
The oil 3 emerges from the passaU~.,y B of directional control valve
VW2 and flows through the return valve VR1 into piston rod space 7. The oil
3 emerging on the piston side of the hydraulic cylinder MY1 is able to flow
back into the tank T via the passageway A-->T in directional control valve
25 VW2. The hydraulic cylinder MY1 is retracted.
