Control device for a hydraulically operated load

The control device for a hydraulically operated load includes a multiway piston valve defining a plurality of working chambers, a plurality of control chambers, a piston having axial and radial bores acting as first choke channels and a control collar cooperating with the control chambers to act as additional choke channels, a piston manometer valve biased by a spring and connected between a pump channel and a return flow channel. A control conduit including at least one choke is connectable via additional choke channels between the pump channel and the return flow channel and has a branch conduit leading to the spring-biased end of the manometer piston. The valve piston is displaceable from its neutral position into an intermediate control position in which in the range of the fine adjustment of the flow the pressure from the load is applied through the control conduit to the manometer piston to provide a load compensated control. In the end control position of the multiway piston the load compensated control is disconnected and maximum through-flow is attained.

BACKGROUND OF THE INVENTION 
This invention relates generally to a control device for a hydraulically 
operated load and more particularly, it relates to a load independent 
control device for regulating flow of a hydraulic fluid including at least 
one multiway piston valve which has a housing and, within the housing, a 
longitudinal boring for slidably guiding the valve piston between a 
neutral position and a plurality of control positions, a fluid inlet 
channel connectable to a pump, a load channel connectable to a load, a 
fluid return channel connectable to a tank, the piston including at least 
one choke channel for selectively connecting in one position thereof the 
control inlet channel to the load channel and in another position thereof 
the load channel to the return channel, a spring-biased piston manometer 
valve connected between the inlet channel and the return channel, and 
being additionally biased by the pressure difference on a choke to 
maintain a constant pressure difference in individual channels, a control 
conduit connected between the inlet channel and the return channel and 
including a branch conduit to additionally bias the piston of the 
manometer control valve. 
From prior art a control device of this type is known in which the piston 
of the multiway valve can take a neutral position and only two working 
positions in which a first control conduit is fully activated whereas 
choking points are operated in response to the movement of the piston to 
choke the flow proportionally to the displacement of the latter. At the 
same time, the load pressure is always transmitted via another control 
conduit to a piston manometer valve. The disadvantage of this known 
control device is the fact that the other control conduit to the load 
cannot be fully shut off and consequently the choking action in the first 
control conduit in the range of a fine adjustment of the device is 
impossible. It is also impossible to increase the effective pressure 
difference to attain maximum working fluid flow to the load. Another 
disadvantage of this known device results from the streaming of the 
working oil to the load via choking non-return valves. This choked 
streaming in the case of a parallel operation of several loads causes a 
limited unloading and leads indeed to an additional energy consumption 
(British Pat. No. 1,401,602). 
Furthermore, a control device for a hydraulic load having a load 
independent flow regulation is known which is designed without any control 
conduit from the pump channel communicating via a choke and a choke 
channel in the piston with the tank. The omission of this control conduit 
means that in the end positions of the piston the influence of the load 
compensation cannot be fully eliminated and consequently the piston 
manometer valve is not exposed to the full pump pressure in lieu of the 
load pressure but to an intermediate pressure which more or less deviates 
from the pump pressure. This intermediate control pressure is to be 
applied to the manometer piston via a branched narrow channel system. It 
is true that this arrangement permits in the end position of the piston of 
the multiway valve to apply full pump stream to the load provided that the 
spring biasing the piston of the manometer valve is correspondingly 
strong; nonetheless, this design results in considerable losses of energy 
in the neutral position of the piston. Moreover, the construction of this 
prior art control device necessitates a hollow piston with non-return 
valves arranged in its interior and thus the whole structure is relatively 
expensive. In addition, this control device has the disadvantage that the 
load pressure due to the location of the non-return valves is tapped off 
at the point where the pressure is reduced about the pressure difference 
caused by the non-return valves and consequently the piston valve 
manometer has to be adjusted for correspondingly higher pressures with the 
result that additional energy losses take place (German Pat. No. 
1,959,764). 
SUMMARY OF THE INVENTION 
It is, therefore, a general object of the present invention to overcome the 
aforementioned disadvantages. 
More particularly, it is an object of the invention to provide an improved 
load independent flow controlling device for a hydraulic load which 
enables in the range of fine adjustment of the flow between the neutral 
position and the end position of the multiway control piston a load 
compensated flow adjustment which is discontinued in the end position of 
the piston so that in this end position a maximum flow to the load is 
possible. 
An additional object of the invention is to provide such an improved 
controlling device which in its neutral position has very low energy 
losses inasmuch as it permits the biasing of the piston manometer valve 
only by a weak spring and consequently the pump can operate only at a low 
pressure. 
In keeping with these objects and others which will become apparent 
hereafter, one feature of the invention resides, in a controlling device 
of the above-described type, in a combination which comprises a 
directional multiway piston valve, the piston of which is movable from its 
neutral position into an intermediate control position in which a first 
choke channel in the valve is made effective and the first control conduit 
is open, the first control conduit being connected to a second choke 
channel provided in the valve for increasing the spring bias on the piston 
of the manometer valve, and the multiway piston being further movable into 
an end control position in which the choke channel is fully open and thus 
made ineffective and the first control conduit is interrupted. 
This combination makes it possible that in the intermediate control 
position of the multiway piston valve in which the fine adjustment of the 
flow takes place is compensated against load variation and in the second 
control position of the piston this load compensation is removed so that 
the maximum flow is admitted to the load. 
Preferably, the second choke channel is shut off in response to the change 
of position of the multiway piston so that the loss of energy in the pump 
can be kept very low in the neutral position of the valve because the 
pressure increase resulting in the second choke channel and normally 
applied against the manometer valve, is removed. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIGS. 1 and 2, the directional control device 10 for 
hydraulic loads A and B includes a connection plate 11, first multiway 
valve 12 and a second multiway valve 13 and a terminal plate 14. The 
construction of both multiway valves 12 and 13 is identical so that the 
description of only one of these valves, for example valve 12, is 
sufficient for disclosing the invention. 
The multiway valve 12 has an axial boring 15 in its housing in which 
control piston 16 is movable in two opposite directions. The interior of 
boring 15 is provided with annular recesses defining respectively an inlet 
port or chamber 17, load chambers 18 and 19 and return flow chambers 21 
and 22. Piston 16 controls in a conventional manner the connection between 
selected chambers. The interior of piston 16 has an axially directed blind 
bore communicating with first choke channels 23 and 24 which are 
adjustable by means of fine adjustment threads and having an effect on the 
stream of working fluid flowing to the load. Near the return flow chamber 
21 in the wall of boring 15, there are consecutively arranged the first 
control chamber 25, the second control chamber 26 and the third control 
chamber 27. Load pressure is always applied to the third control chamber 
27 via axial and radial bores 28 in piston 16. In the range of the first 
and second control chambers 25 and 26 the periphery of piston 16 is 
provided with annular choking recesses or channels 32 and 33 separated by 
control collars 29 and 31 to modify the flow connection between the first 
control chamber 25 and the second control chamber 26. 
Control device 10 cooperates with a pump 54 from which pressure fluid inlet 
channels 35 and 36 with non-return valves 37 lead into inlet chamber 17. 
Device 10 further comprises a branched return channel 38 which connects 
all return fluid chambers 21 and 22. In connection plate 11 the first 
control conduit 39 branches from pump channel 34 and continues via the 
first choke 41 and through the second control chamber 26 and the first 
control chamber 25 of respective multiway valves 12 and 13 to join return 
channel 38 in terminal plate 14. In connection plate 11 there is further 
provided a piston manometer valve 42 having its piston 43 biased by spring 
44. Valve 42 controls the connection between the pump channel 34 and the 
return channel 38. Piston 43 of the manometer valve 42 is furthermore 
biased from the side opposite the spring 44 by the pressure from pump 
channel 34 and on the side of biasing spring 44 being additionally biased 
by a branch conduit from the first control conduits 39, the branching 
taking place downstream of the first choke 41. This branch conduit from 
the first control conduit 39 is at the same time connected to a second 
control conduit 45 through which it can be acted upon by the instant load 
pressure since channel 47 leads through the first control chamber 27 and a 
non-return valve 46, provided in both multiway valves 12 and 13, to the 
second control conduit 45. Pressure limiting valves 48 safeguard the 
spring loaded end of piston 43 of manometer valve 42. 
Referring now to the simplified circuit diagram of device 10 in FIG. 2, 
piston 16 of each valve 12 or 13 is movable from a neutral position 51 
into a left-hand or right-hand intermediate control position 52 and 
furthermore into corresponding end positions 51. In the intermediate or 
first control position 52 the first choke channel 23 (or 24) becomes 
effective and at the same time the load pressure is tapped off via one of 
radial bores 28. In addition the second choke channel 33 (or 32) is 
connected into the first control conduit 39. In the end or second control 
position 53 the first choke channel 23 (or 24) is no longer effective and 
each connection is fully open while the first control conduit 39 is 
interrupted. First control position 52 extends over a considerable range 
of travel of piston 16 which covers practically the whole range of the 
fine adjustment of the flow whereas the second control position 53 covers 
a relatively small portion of travel of piston 16 and corresponds 
practically to the end working position of the piston. 
The operation of control device 10 is as follows: 
If pistons 16 of both multiway valves 12 and 13 are in their neutral 
position, oil or other working fluid delivered by pump 54 flows through 
piston manometer valve 42 back into return channel 38 formed in connection 
plate 11. Pressure generated by pump 54 is determined by the force of 
pressure spring 44 biasing from one end piston 43 of manometer valve 42. 
If piston 16 of one multiway valve, for example of valve 12, is shifted 
from its neutral position 51 (FIG. 2) so the inlet chamber 17 is connected 
via one of choke channels 23 or 24 to load chamber 18 or 19. For instance, 
if load chamber 18 is connected to inlet chamber 17 via choke channels 23 
and 24, the other load chamber 19 is pressure-released through flow return 
chamber 22. If load chamber 19 is connected to inlet chamber 17, load 
chamber 18 is pressure-released through return chamber 21. At the same 
time, the load chamber 18 or 19 while connected to inlet chamber 17 is 
connected through axial and radial bores 28 in piston 16 to the third 
control chamber 27 which in turn communicates via a second control conduit 
45 and a non-return valve 46 with the spring-biased end of piston 43 of 
manometer valve 42. The first control conduit 39 which in the neutral 
position 51 was open becomes in the first control position 52 choked 
through the second choke channel 33 or 32. Consequently working oil 
delivered from pump channel 34 through the first choke 41 can no longer 
reach the tank through the open first control conduit 39 but is subject to 
choking. Choke channel 33 or 32 is preferably designed to be as large as 
to create in the second control channel 26 and thus in piston 43 of piston 
manometer 42 only such pressure which produces the desired pressure drop 
across choke channels 23 or 24 in the range of the fine adjustment of 
piston 16 provided that no load pressure builds up in load chambers 18 and 
19. Since the pressure in the second control chamber 26 supplements the 
bias of spring 44 on piston 43 of manometer valve 42, the piston 43 moves 
in closing direction to such an extent until pressure builds up in pump 
channel 34 which is sufficient for operating the load. Simultaneously 
additional working oil flows due to the load pressure from load chamber 18 
or 19 via axial and radial bores 28 in piston 16 into the third control 
conduit 45 while the pressure of inlet working fluid is admitted in load 
chamber 18 or 19. Due to the fact, however, that choke channel 33 remains 
unchanged, an increased pressure builds up also in the second control 
conduit 45 which acts on spring biased end of piston 43 of manometer valve 
42. As soon as the load changes, a pressure drop is created at the inlet 
side of load chamber 18 or 19 and this pressure drop affects through the 
bores 28 the pressure fluid control system and prevents a further increase 
of the pressure. In this manner, a load compensated control of the load is 
possible over a range of the fine adjustment in which choke channel 23 or 
24 is controlled proportionally to the deflection. 
As soon as the second control position 53 of piston 16 is reached at the 
end portion of its stroke, the first control conduit 39 is completely shut 
off by the control sections of piston 16 adjoining collars 29 and 31. 
Simultaneously choke channels 23 or 24 become uneffective and the 
connection to the load is fully open and the pressure compensating meter 
piston 43 interrupts by the force of biasing spring 44 the connection to 
flow return channel 38. The whole amount of working fluid delivered by 
pump 54 flows therefore to the load with the minimum pressure drop 
determined by the given structure and the load compensation is 
disconnected. 
In this manner the device of this invention makes it possible that in the 
neutral position of piston 16 the entire amount of working fluid delivered 
by the pump is returned to the tank with minimum pressure drop, whereas in 
the range of the fine adjustment of the flow load compensated control 
takes place with very low power losses and the through-flow is 
proportional to the adjusted area of control openings, and in the end 
position of the piston the load compensation is switched off and maximum 
flow of working oil to the load takes place. 
If pistons 16 of both multiway valves 12 and 13 are operated in parallel to 
resume the first control position 52 in the range of fine adjustment, 
respective choke channels 33 or 32 become connected in series so that 
control pressure is correspondingly increased. A further increase of the 
control pressure and thus the amount of the through-flow is attainable by 
designing the arrangement of respective borings assigned to choke channels 
23 and 24 for tapping off the load pressure such that in the course of the 
stroke of piston 16 the initially active boring plunges into the inlet 
chamber 17 and then transmits load pressure increased about pressure drop 
between inlet chamber 17 and load chamber 18, to piston 43 of manometer 
valve 42. Non-return valves 48 serve to safeguard the maximum pressure and 
prevent, during the parallel operation of valves 12 and 13, the streaming 
of pressure fluid from the direction of high load pressure to the low load 
pressure. 
FIG. 3 shows another embodiment of control device 60 of this invention 
having a first multiway valve 61 which deviates from multiway valve 12 
according to FIGS. 1 and 2 in that the second choke 62 is no longer 
arranged on piston 63 itself but is arranged in the first control conduit 
39 in the housing upstream of piston 63. This results in a simpler 
structure of control device 60 because control collars on the piston are 
dispensed with. The second choke 62, however, is not disconnectable in the 
neutral position of piston 61 so that a higher pressure during the neutral 
circulation takes place. The second multiway valve 64 is now designed 
without the second choke since its function is taken over by choke 62 in 
the housing. The second choke 62 can be arranged also in connection plate 
11. 
FIG. 4 shows still another embodiment of the control device of this 
invention which differs from the preceding control device 60 according to 
FIG. 3 in the following points: The second choke 71 is arranged in the 
first control conduits 39 in the terminal plate 74 downstream of the first 
valve 72 and the second valve 73. In addition, the second control conduit 
45 as shown in FIG. 3, is eliminated and the load pressure is directly 
transmitted through the first control conduit 39 and through corresponding 
passages in respective pistons 75 and through non-return valve 76. In this 
manner the most simple and space-saving construction of the control device 
of this invention is achieved. Nevertheless, the structure of piston 75 
has to be provided with non-return valves 76 and the effect of second 
choke 71 cannot be disconnected when pistons 75 are in their neutral 
position. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. For example, 
instead of the second control conduit 45 in which load pressures are 
tapped off in parallel (FIG. 1), each channel 47 can be arranged in the 
same housing and directed into the first control conduit 39 upstream of 
the second control chamber 26. Also a modified structure of multiway 
valves can use borings 28 which instead in the piston are arranged in the 
housing. It is also possible to employ multiway valves having connection 
to only one load instead of two loads and the layout of working and 
controlling chambers can be different from that as illustrated in the 
preferred embodiments and also the control edges and chokes on respective 
pistons of the multiway valves can be made differently without departing 
in any way from the spirit of this invention.