Patent Application
20180372126
The present invention relates to the field of hydraulic valve devices with open circuit and multiple working elements or sections, wherein a suitable entry side allows managing an LS pump according to predetermined management methods.
It is noted that the protection extends to all hydraulic distributors having the claimed valve device.
More generally, open-center directional valves are conventionally combined with constant displacement pumps. Such a solution has energy limits in that also in the case of drives where only part of the available flow rate would suffice, actually the whole flow rate of the pump is brought under pressure and then the excess is laminated directly to the tank, with a useless dissipation of energy and heating of the oil.
For this reason, circuits have been devised that use variable displacement pumps of various types with suitable management systems.
A variable displacement pump used in conventional machines is the positive control pump. These are characterized in that the displacement varies as a function of a control pressure according to a regulation curve of the displacement depending on the control pressure of the type in
Another example of a variable displacement pump is the LS pump, in which the pump displacement varies so as to keep a constant pressure drop on a choke.
Along with these pumps, it is conventional to use LS distributors with closed-center elements and relative local compensators and a series of selectors to select the highest LS signal among the driven elements.
These distributors ensure excellent features to the circuit but they are expensive distributors and the application does not always justify the use thereof.
Open-enter hydraulic systems have been implemented for these which are able to manage an LS pump:
It is not even possible to set a maximum flow rate if not the maximum one of the pump which is obtained by closing the LC at the end of the stroke.
Also in the concurrent movements, the total flow rate to the utilities will depend on the loads, in addition to the fact that this will be divided between the two utilities on the basis of the reciprocal loads and as these loads vary, the division among the driven utilities varies and so does the sum of the single flow rates to the utilities.
An object of the present invention is to provide a valve device which, acting only on the entry side of a standard directional crossing valve, allows managing an LS pump according to predefined features that will be described within a simple, rational and cost-effective solution.
These and other objects are achieved with the features of the invention described in the independent claim 1. The dependent claims describe preferred and/or particularly advantageous aspects of the invention.
One aspect of the invention is to provide a valve device which includes a flow rate regulation group compensated on the bypass line upstream of the elements of the valve device and wherein said regulator includes a compensator piloted spool that imposes a constant pressure stage, and thus a constant flow rate, through a choke.
Moreover, the device includes a choke, located along the load line, so that the passage through such a choke opens proportionally to the control pressure value taken from the by-pass line downstream of the compensated flow regulator and upstream of all the elements.
Downstream of said choke, the LS signal is picked which feeds the LS pump which sends a flow rate proportional to the opening of the choke, in turn proportional to the control pressure, in turn it is proportional to the stroke of the spools, as will be apparent from the following description.
With this solution, the valve device is capable of making, in single drives, the flow rate to the utilities independent of the load and only a function of the spool stroke; in multiple drives, at least fixing the sum of the single flow rates to the utilities, although the division between the single utilities remains dependent on the loads.
This means that the flow rate to the utilities is independent of the load, meaning that given a certain stroke of the spool, the flow rate to the utilities is fixed and does not vary with the variation of the pressure to the utility.
Another aspect of the invention is to prevent a significant and unnecessary energy dissipation if the bypass line, or the crossing line, is closed completely by the drive of the spools of the elements making up the valve device.
Such a drawback is solved by the invention by inserting, before the picking point of the signal that returns to the compensator piloted spool and subsequently proportionally actuates the choke on the load line, a second choke: by closing completely the by-pass line LC and opening a relief valve, the flow rate also goes through the second choke, thereby causing a suitable reduction of the flow rate set by the compensator piloted spool, a value that will be the minimum necessary to keep the relief valve open.
This and other features will be more apparent from the following description given purely by way of non-limiting example in the accompanying drawings.
With reference to
The supply is connected in P1 to the entry side FE.
One or more elements E1, E2, . . . En (in the case 2 elements E1 and E2) of the crossing type that allows connecting the PA pump and the tank to the various utilities through the uses (A1, B1, A2, B2).
A bleeding side FS keeps the flow rates from the bypass line LC separate from those coming from the return of the utilities and from the bleeds of the valves and connects them both to tank T through two separate lines.
In essence, the valve circuit of the valve device includes at least:
Contrary to what happens in standard crossing valve distributors, where they all are connected so as to come out of a single coupling, in the present invention the line and thus the flow rate flowing into the by-pass line LC is kept separate with respect to the lines of the return flow rates of utilities and valves, which equally go to tank T but with two separate couplings, that is:
From the above description, the pump flow rate in the entry side is divided into two channels:
The presence of a flow rate regulator group of the two-way compensated type is also noted, placed only on the bypass line LC and in the side, before all the sections E1 . . . En.
Specifically, the flow regulator group consists of:
The strength of a spring M and the pressure of the control line P, taken downstream of chokes 2 and 5, acts on the one side on piloted spool 3, while on the other side and in closing, the pressure of line 9 taken between the piloted spool and the choked passage 2.
Spring M therefore imposes a suitable stand-by through the chokes, whose value must be lower than the stand-by set by the LS pump.
Said regulator group is calibrated, for example, to 15-20 l/min on the line LC.
Downstream of the flow rate regulator group and on the bypass line LC upstream the first element E1, the control pressure P is picked which acts by opening a choke, in this case a proportional opening tray 8, along the load line 4, the value of which will be determined by the load losses of the flow rate set by the compensated flow regulator through the bypass line LC.
Since the flow rate is constant, the load losses and thus the control pressure are proportional to the stroke of spool Cn and only to the stroke of spool C1. Since the passage through said choke 8 is proportional to the control pressure P, it is therefore proportional to the stroke of the spools.
The LS signal taken downstream of said choke 8 arrives at the LS PA pump; then, the latter will send a flow rate proportional to the opening of choke 8, in turn proportional to the control pressure, in turn proportional to the stroke of the spools.
Operation
Upon start up, the LS pump sends the minimum flow rate to generate the stand by. This corresponds to the calibration flow rate of the compensated flow regulator with lower stand-by. In fact, once such a flow rate has been reached, the regulator chokes to prevent the flow rate from exceeding the calibration, increasing the pressure in P1 up to the stand-by value of the LS pump.
Said flow rate then flows all through the compensator tray 3, then through the by-pass line LC and arrives to tank T by line C.
As said, downstream of the flow rate regulator group (piloted spool 3+choke 2) and on the bypass line LC upstream the first element E1, the control pressure P is picked which acts on the proportional choke 8, the value of which will be determined by the load losses of the flow rate through the bypass line LC.
The provision of a second choke 5 is also noted, again placed on the control line 5, in addition to a relief valve 7, in the example calibrated at 30 bar.
Therefore, the LS pump still generates the calibration flow which, along with the passages through the LC, must be such as to generate a control pressure P slightly lower than that which generates the opening of choke 8.
In the central position of the spools, the LC is open while U is closed.
The LS signal is to discharge through the bleed. The LS signal arrives at the LS pump which intervenes so that the pressure on the PA pump supply is equal to the sum of:
Disregarding the distributed load losses, this is obtained from the LS pump by supplying the flow rate able to generate, through the flow rate regulator 3, choke 2 and the by-pass line LC that crosses all the elements in series, a load loss equal to the stand-by value of the LS pump corresponding to the constant pressure drop imposed by the pump between the supply and the load-sensing pressure.
Now the flow rate of regulator 3 to that supplied by the pump and is calculated so as to generate a pressure drop through the choke 2 higher than the stand-by of the flow regulator 3. This means that the regulator intervenes by choking the LC so as to limit the flow rate through choke 2 to that single flow rate value able to generate, through choke 2, a load loss equal to the value of the stand-by of the flow regulator 3.
Actuation of a Spool
What happens when actuating a spool individually, such as the one indicated with C1, is now described. First, the connection between the load line 4 and the corresponding utility is opened (along lines A1 or B1). At the same time, the passage through the by-pass line LC narrows, whereby load losses increase, as does the control pressure P on choke 8 taken after the compensator piloted spool 3.
Increasing the control pressure of the pump regulator leads to the opening of the passage through choke 8, thus setting the supply P1 in communication with the LS signal line. BY circuiting the P1 on the LS, the pressure in P1 increases progressively up to exceeding the load pressure on the driven utility. At that point, a flow rises through choke 8 whose value will be determined by the value of the stand-by at which the LS pump is calibrated.
The compensated flow regulator group, however, maintains a constant flow rate through the bypass line LC: therefore, the load losses, the control pressure, the opening of choke 8 and the flow rate to the utility through the load line 4 remain constant, irrespective of the load.
Moreover, since the flow rate is constant, the load losses and thus the control pressure are proportional to the stroke of spool C1 and only to the stroke of spool C1, the opening of choke 8 and thus the flow rate to the utility are a function only of the stroke.
By further actuating spool C1, the load losses through the bypass line LC, and thus the control pressure P tend to increase, thus further increasing the opening of choke 8 and the flow rate supplied by the LS pump that will flow towards the utility by the intervention of the flow regulator that maintains a constant flow rate on the bypass line LC.
It follows from the above that in the single drives, the flow rate to the utilities is independent of the load but only a function of spool C1. It follows that, in single drives, it is also possible to set a maximum flow rate to the utility.
Actuation of Multiple Spools
Assuming now that a second spool is actuated, that indicated with C2, the bypass line LC tightens further, resulting in increased load losses, increased pressure just downstream of the compensated flow regulator group, then increase in pressure P, resulting in an increase of the passage through the proportional choke 8 and thus of the flow rate supplied by the LS PA pump.
The division of the flow rate between the two utilities depends on the reciprocal loads but the total flow supplied by the LS pump is independent of the utilities.
If, at the end of the stroke of spool C2 the LC is closed, the flow rate set by the compensator flows to bleed through the relief valve 7, set at the pressure that leads the proportional choke 8 to the maximum aperture which corresponds to the maximum flow rate of the LS pump: the full flow rate at which the flow rate regulator is calibrated would directly go to bleed with a significant and useless energy dissipation.
This problem is solved by the invention by inserting, before the picking point of the signal that returns to piloted spool 3 of the compensator and then to choke 8, a second choke 5: until the relief valve 7 intervenes, no oil passes whereby the flow rate set by the compensator is determined only by the first choke 2. By closing completely the by-pass line LC and opening the relief valve 7, the flow rate also goes through the second choke 5, thereby causing a suitable reduction of the flow rate set by the compensator piloted spool 3, a value that will be the minimum necessary to keep the relief valve open.
In summary, the valve device comprises, on the bypass line LC only and upstream of the first element E1, a flow rate regulator group comprising at least one compensator piloted spool 3 and a choke 2; a control signal P connected to said flow rate regulator and to the proportional choke 8, whose passage increases as the control pressure increases; said control signal P being picked downstream of the compensator piloted spool 3 and after said choke 2.
The variable displacement pump LS is managed by the LS signal, where now, however, the LS signal is no longer taken downstream of the fixed choke 8 but of tray 2, which generates a variable choke with the stroke.
Then, the LS pump imposes a constant P through tray 8 and thus a flow rate which only depends on the stroke of tray 8 and which is constant at the same stroke.
Choke 2 is instead managed by the flow regulator 3 which imposes a constant ⋅ P through choke 2, and thus a constant flow rate through choke 2.
Finally, it is noted that “load line” means the line connecting the pump supply to utilities A1, B1, A2, B2 . . . through spools C1, C2, . . . which in central position isolate the load line 4 from the utilities. In the subject patent, tray 8 is placed on this line as a function of choke proportional to control P.
The spools are C1, C2, . . . which in central position:
By actuating the spool:
Component 3 is substantially a piloted spool that keeps ⋅ P constant through the fixed choke 2.
| Number | Date | Country | Kind |
|---|---|---|---|
| ITUB2015A009571 | Dec 2015 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/081423 | 12/16/2016 | WO | 00 |
