Apparatus for providing relief to a working chamber

For the relief of a highly pressurized hydraulic liquid in a working chamber of pilot controlled 2/2 poppet valve is used. The working chamber is further connected to a pressure relief valve, the output of which is connected to a control conduit extending between a control chamber of the 2/2 poppet valve and the pilot valve. The apparatus of the invention requires a shorter period of time for the pressure relief without the danger of relief noise.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus for providing relief to an operating 
chamber of a hydraulic unit which is under high pressure. More 
specifically, the invention relates to such an apparatus for the working 
chamber of a hydraulic cylinder. 
It is known to provide pressure relief (decompression or venting operation) 
by means of a pilot actuated 2/2 control valve (a so-called poppet valve 
or logic unit). So as to avoid a relief noise or relief blows, the opening 
movement of the poppet of the 2/2 control valve has to occur with a speed 
as low as possible. For that purpose the pilot oil which is used for the 
actuation of the control poppet of the main or poppet valve is removed 
from the control chamber of the 2/2 poppet valve via a correspondingly 
small dimensioned fixed throttle or orifice. This kind of pressure relief 
requires a relatively long time until the pressure in the working chamber 
reaches the level of the tank pressure. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an apparatus for the 
relief (venting) of pressure from a working chamber such, that the time is 
kept short which is necessary for the highly pressurized working chamber 
to achieve the level of the tank pressure. The venting operation should 
occur without taking the risk that relief noise or relief blows occur. 
According to an aspect of the invention an apparatus is provided for 
allowing pressure relief for a working chamber which is under high 
hydraulic pressure. That apparatus comprises a pilot controlled 2/2 poppet 
valve. The pilot controlled 2/2 poppet valve comprises a control chamber 
(in which a control pressure acts) as well as a poppet (i.e. a control 
spool having a closing member). Between the control chamber of the 2/2 
poppet valve and the pilot valve a (first) throttle is located. The area 
(also called control surface) of the poppet subjected to the pressure in 
the control chamber is larger than the area of the poppet which is 
subjected to the user pressure. The control pressure acts in the direction 
of closing said 2/2 poppet valve while the user pressure acts in the 
direction of opening said poppet. The working chamber is additionally 
connected to a pressure relief valve. The output of said pressure relief 
valve is connected to the control connection which extends between the 
control chamber of the 2/2 poppet valve and the pilot valve. 
The additional connection of the working chamber to the pressure relief 
valve causes--at the time the pilot valve is switched--initially a relief 
of the pressure chamber to a pressure value to which the pressure relief 
valve is adjusted. During that operation the pressure medium or working 
liquid flows via the pressure relief valve and via the pilot valve to the 
tank. During said first relief phase the main valve (i.e. the 2/2 poppet 
valve) still remains closed due to the connection to the pilot valve, 
because there is a build-up of pressure due to the working liquid flowing 
across the pressure relief valve. This is due to the fact that the control 
surface of the poppet which is subjected to said pressure build-up is 
larger than the annular surface or area of the poppet which is subjected 
to the working pressure of the user. As soon as the pressure build-up has 
reached a value which is no longer sufficient to keep the poppet in its 
closing position, a second relief phase is initiated. For the second 
relief phase the poppet opens the connection between the working chamber 
and the tank. The opening speed of the poppet is determined by the 
flow-cross-section of the first throttle assigned to the control chamber 
of the poppet valve. The control liquid displaced from the control chamber 
of the poppet valve during the opening movement of the poppet flows across 
said first throttle. Due to the existence of said two phases of relief the 
time required for the pressure relief of the user can be adjusted to an 
optimum value without having to be afraid of a relief blow or relief 
noise. 
Preferred embodiments of the invention are disclosed in the dependent 
claims.

The FIGURE shows a user in the form of a hydraulic cylinder 1. The 
hydraulic cylinder 1 comprises a working chamber 2 connected via a working 
conduit 3 to a check valve 4, which in turn is connected to the pressure 
side of a pump 5. A conduit 6 branches-off said working conduit 3 and 
extends towards the input of a 2/2 control or poppet valve 7. The poppet 
valve 7 has a poppet which in turn comprises a control spool 20 and a 
closing member 28. The 2/2 poppet valve (poppet unit) has two switching or 
operating positions, namely an open position and a closed position. The 
2/2 poppet valve is a so-called logic valve and is hydraulically 
controlled by means of a pilot valve 8. Details about a poppet valve can 
be found on pages 4-28 through 4-36 and 5-56 through 5-68 of the book 
entitled "USING INDUSTRIAL HYDRAULICS", published by HYDRAULICS & 
PNEUMATICS Magazine, Cleveland, Ohio 44114. The 2/2 poppet valve comprises 
a control chamber 9 which is connected via a first throttle 10 and a first 
additional throttle 11 to the P-port of the pilot valve 8. This connection 
is provided by a control conduit 12 within which the two throttles 10 and 
11 are located. Control or pilot liquid is taken from the pump conduit 3 
by means of a pilot conduit 13 and is supplied via a second additional 
throttle 14 to the pilot conduit 12. From there, the pilot liquid passes 
to the control chamber 9 via said first throttle 10. A pilot conduit 
section 15 leads from the pilot conduit 13 to a pressure relief valve 16. 
The output 17 of said pressure relief valve 16 is connected to a pilot 
conduit 18 which in turn is connected to the pilot conduit 12. 
The pilot control valve 8 has two (switching) positions referred to "a" and 
"b". The pilot valve 8 is shown in its closed position "a" which will be 
assumed if the solenoid M is energized. In the position "a" of the pilot 
valve 8 the poppet, and specifically its closing member 28, is maintained 
in its closing position and thus, the connection of the working conduit 6 
to the tank conduit 21 is blocked. The closing member 28 is kept in its 
closing position due to the pilot pressure acting in the control chamber 9 
and upon the control spool 20 together with the force of a closing spring 
19. 
The pressure relief valve 16 remains in its closing position until the 
working pressure, which acts against the force of a pressure spring 22 via 
a control conduit section 26, reaches the pressure value for which the 
closing spring 22 is adjusted. As soon as this situation occurs and the 
working pressure goes beyond the pressure value adjusted at the pressure 
spring 22, the pressure relief valve 16 opens and connects its input 27 
with its output 17. 
In case that the pilot valve 8 is moved from the closed position "a" (as 
shown) into its connecting position "b" by means of the pressure spring 
29, because the solenoid M is de-energized--and thus a connection is 
provided via the port A and the control conduit 23 to the tank 24--the 
working liquid flows from the working chamber 2 to the tank via: the 
working conduit 3, the control conduit 13, the pressure relief valve 16, 
the control conduit 18, the first additional throttle 11 in the control 
conduit 12, the pilot valve 8, and the control conduit 23. The amount of 
liquid flowing to the tank 24 is limited by the free cross-section of the 
throttle 11. Thus, simultaneously, there will be a pressure build-up in 
the control conduit 12. This pressure build-up will act upon the control 
chamber 9 via the throttle 10 and will initially hold the poppet, i.e. the 
closing member 28 in its shown closed position. As soon as the pressure in 
the working chamber 2 has decreased so far that the pressure relief valve 
16 closes in accordance with its adjusted pressure, and thus no working 
liquid will be supplied to the control conduit 12, the pressure build-up 
in the control conduit 12 and, consequently, also in the control chamber 9 
decreases. As a consequence the working pressure acting upon the annular 
surface or area 30 of the control spool 20 (of the poppet) acts upon the 
closing body 28 against the small force exerted by the closing spring 19 
and moves said poppet, i.e. the closing body 28 into the opening direction 
and thus a direct connection between the working chamber 2 and the tank 
port 21 is provided, so that the remaining relief occurs for the working 
chamber 2. The speed of the opening movement of the poppet, i.e., the 
closing member 28 is determined by the free cross-section of the throttle 
10 or, in case such a throttle is not provided, by the throttle 11. This 
is so, because the control liquid displaced during the opening movement of 
the closing body 28 has to passed across said throttle to the tank 24. 
Initially, by means of the pressure relief valve 16, the high pressure in 
the working chamber 2 is decreased to an intermediate pressure is 
determined by the inner resistance of the pressure relief valve 16. The 
removal or venting of the remaining pressure via the 2/2 poppet valve 7 
can be carried out quickly, in as much as a relief shock is not expected 
in the lower pressure range. 
Therefore, in contrast to the prior art the first throttle 10, which 
determines the opening speed of the closing member 20 of the 2/2 poppet 
valve 7 can be of relatively large design or can be deleted altogether, 
thus correspondingly increasing the speed of the opening operation of the 
2/2 poppet valve 7. It is thereby possible to limit to a small period of 
time the total time required for the relief of the working chamber 2. 
Instead of connecting the outlet 17 of the pressure relief valve 16 via the 
control conduit 18 to the control conduit 12 and thus to the pilot valve 
8, it is also possible to connect the control conduit 18 via a separate 
2/2 control (poppet) valve to the tank. In this case a matching or tuning 
operation between the additional 2/2 poppet valve and the pilot valve 
would have to be carried out in such a manner that initially said 
additional poppet valve is switched into its open or passing position for 
removing the working fluid via the pressure relief valve, and, thereupon, 
the pilot valve 8 for the 2/2 poppet valve (logic valve) 7 is switched 
into its open or passing position. 
The relief apparatus of the invention is preferably formed by three plate 
structures I, II, and III. Plate structure I is adapted to receive the 
logic valve 7, plate structure II is adapted to receive the pressure 
relieve valve together with the two throttles 14 and 11, and the plate 
structure III is adapted to receive the pilot valve 8. 
The throttle cross-section of the second additional throttle 14 is smaller 
than the flow cross-section of the first additional throttle 11. This 
assures that a sufficient pressure build-up occurs in the conduit 12 when 
the pressure relief valve 16 is in its open position so as to maintain the 
closing body 20 in its closing position. It is also assured that in the 
closed position of the pilot valve 8 control liquid for closing the 
closing body 20 can be supplied from the user and from the pump, 
respectively, via the throttle 14. It is possible not to use the throttle 
10 if the second phase of relief is to occur very fast.