GB2073564A - Plough turn-over mechanism - Google Patents

Abstract

The invention relates to a hydraulic turning mechanism for a two-way turn-over plough which can be attached to a tractor, having a double-acting piston-and-cylinder unit 5, 2 and a reversing device reacting to the operation of a tractor valve 28 with a control piston 10 which changes over depending on pressure and which has two active surfaces of different size. The control chamber 25 of the control piston is connected via a flow path which is constricted and can be controlled by a valve member 14, to the return, and the valve member holds the flow path open so long as a predetermined pressure in the control chamber or a predetermined pressure difference between control chamber and return is not exceeded. Thus assurance is provided that, after the double stroke of the piston-and-cylinder unit has been completed, the control piston moves back in a short time to its initial position, without any special controls of the tractor valve. The turning mechanism is therefore ready for a fresh turning after a short time, particularly when only the pressure supply line can be connected up and disconnected through the tractor valve and the return line is taken directly back into the tank. <IMAGE>

Description

SPECIFICATION Hydraulic turning mechanism for a two-way turnover plough which can be attached to a tractor The invention relates to a hydraulic turning mechanism for a two-way turn-over plough which can be attached to a tractor.

In such turning mechanisms the problem exists, inter alia, of rendering possible a reliable and rapid return of the control piston into the initial control position after termination of the double stroke and after the cessation of the action of the external pressure. The possibility, which is trivial with a two-line connection but still requires an additional movement of the hand, of changing over the control valve at the tractor, should be avoided and is not even possible with a tank line laid separately. A practically constructed turning mechanism in accordance with the German Patent Application PS 007992.6 had a constricted connection between control chamber and return, which was interrupted before the second control position was reached. With the pressure medium at operating heat, the return time amounted to about 2 seconds, all requirements thus being met.

With cold outside temperatures, the return time was extended to 15 seconds particularly when the control valve on the tractor was comparatively tight and pressure-holding hoses were used in the system.

Although even this time is sufficient during normal field work, a shortening may be desirable in special cases. Such a shortening could also be achieved by a permanently open constricted connection between control chamber and return. Such a connection, however, leads to difficulties at least when small throttles, for example in the form of nozzles, are used to adjust the stroke and control speeds, the cross-section of which throttles is already in the range of magnitude of the constricted connection.

In such a case there was the risk of building up inadequate pressure and it is then worth striving for to use a connection which is only opened intermittently.

It is the object of the invention to provide a connection which is closed with high pressures in the control chamber and nevertheless permits a more rapid return to the initial control position even with a certain retaining of pressure by hoses or the like and with a cold pressure medium.

According to the present invention there is provided a hydraulic turning mechanism foratwo-way turn-over plough which can be attached to a tractor, having a double-acting piston-and-cylinder unit and a reversing device with a) a housing b) connections in the housing, namely b1) a working connection for a first working chamber of the piston-and-cylinder unit, b2) a working connection for a second working chamber of the piston-and-cylinder unit, b3) a pressure connection which can be connected to at least one pressure medium source through an external control valve, b4) a return connection which is or can be connected to a storage container or intermediate reservoir, c) a control piston in the manner of a 4/2-way valve piston which is adapted for sliding in the housing, comprises two control positions and is permanently loaded by a return spring in the direction of one of the control positions, d) a first active surface on the control piston which is permanently acted upon by the pressure of the pressure medium source, is directed counter two the return spring and is small in comparison with the total cross-section of the control piston, e) a connection, which is opened after a predetermined travel of the control piston, between the pressure connection and a control chamber bounded by a second active surface on the control piston which is likewise directed counter to the return spring and is large in comparison with the total cross-section of the control piston, characterised in that f) there is a flow path (gaps 21 and 24), which can be controlled by a valve member (seat valve 14), between the control chamber (25) and the return, g) which even when the valve member (seat valve 14) is fully open contains at least one constriction (gap 21), h) the valve member (seat valve 14) being permanently loaded by a spring (19) acting in the sense of opening the flow path, i) and opening after the predetermined travel of the control piston (10) below a specific pressure drop between control chamber (25) and return or below a specific pressure in the control chamber (25) and closing above the specific pressure.

The invention is based on the fact that with a closed connection in the second control position with the face of the control piston fully loaded, the return spring only becomes effective when the pressure in the control chamber has dropped to 4 bar for example. Particularly with pressures becoming lower, the time for a specific pressure drop is extended. Furthermore, starting from the consideration that manipulations at the control valve of the tractor are not possible and that the use of pressure-storing hoses cannot be dispensed with, through the solution according to the invention, a connection between control chamber and spring chamber of the control piston is established already with a considerably greater pressure drop than 4 bar.

In an example of embodiment, the pressure drop to 60 bar was determined with a maximum pump pressure of 180 bar. Naturally, the amount of pressure medium flowing through a feed throttle must be great enough to ensure a pressure head of 60 bar at the constricted connection because otherwise the connection could not be closed.

The invention will be explained in more detail with reference to an example of embodiment illustrated in the Figures.

Figure 1 shows a turning mechanism during the The drawing(s) originally filed were informal and the print here reproduced is taken from a later filed formal copy.

first phase of the stroke.

Figure 2 shows the same turning mechanism after the switching overto the second phase of the stroke.

Figure 3 shows, illustrated on a larger scale, the seat valve in the opened state.

A turning mechanism 1 has a cylinder 2 with a cylinder head 3. In the interior of the cylinder 2, a piston 5, which is connected to a piston rod 4taken to the outside and slides in a sealed manner, partitions off a first working chamber 6, which surrounds the pistom rod 4, and opposite which, atthe farside of the piston, is a second working chamber 7. Pm vided in the cylinder head 3 is a bore 9 which is closed to the outside by a sealing stopper 8 and in which a control piston 10 is adapted to slide. The bore 9 has a flat bottom 11, into which a pressure passage 12 leads centrally. inside the cylinder head 3, the pressure passage 12 is in communication with a pressure connection 13.The edge between the pressure passage 12 and the bottom 11 serves as a seatfora seat valve 14 which has a conical closing member with a stem 15 disposed at the back. The stem 15 is guided with clearance in a part 16 having a smaller diameter of a stepped bore penetrating lengthwise through the control piston 10, the part 17 having a larger diameter being adjacent to the sealing stopper 8. The stem 15 is further provided, at its portion projecting into the part 17, with a spring washer 18 or the like, on which there rests a spring 19 which is supported by its other end on the sealing stopper 8. A second spring 20 acts on the step between the parts 16 and 17 and hence directly on the control piston 10.The annular gap between the stem 15 and the part 16 of the stepped bore is designated by 21 and for reasons of clear illustration is shown considerably larger than would correspond to a real construction. The end face 22 of the control piston 10 forms, together with the annular face 23 of the cone of the seatvalve 14 following on the stem 15, a further seat valve which can open and close a gap 24 situated between the faces 22,23. The space between the bottom 11 and the end face 22 is designated as a control chamber 25. The bore 9 is connected, through a passage 26, to a return connection 27 which in turn is in communication with a connec- tion A of an external control valve 28.The control valve 28 also has a connection B, which is connected to the pressure connection 13, and a connection P which is connected to a pressure-medium source 2% as well as a connection T leading to a storage con tainer30. The control valve has three control posi tions "o", "a" and "b" corresponding to the connections P-T, P-B and A-T as well as P-A and B-T. The bore 9 widens out, seen from the bottom 11, to three annular grooves 31,32 and 33 axially removedlfrom one another. A connection to the pressure connection 13 leads into the annulargroove33. Fromthe annular groove 32, a conduit leads to a working con nection 34 which is connected to the working chamber 6 through a conduit 35.Leading from the annular groove 31 is a passage 36 which leads via a releasable non-return valve 37 and from there through a passage 38 to the working chamber 7. The releasable non-return valve has, as a closing member, a ball 40 which is loaded by a spring 39 and which automatically opens in the direction of the working chamber7 but can be released by a releasing piston 41 which is loaded by the pressure atthe working connection 34. The control piston 10 has, at its outer wall, two annular grooves which, seen from the bottom 11, are designated by 42 and 43. In the initial position of the control piston 10 (Figure 1),the annular grooves 31 and 42 are connected while the annular groove connects the annular grooves 32 and 33.In the second control position of the control piston 10 (see Figure 2), the annular groove 32 is connected to the annular groove 42, while the annular groove 31 has a direct communication to the control chamber 25. A transverse bore 44 connects the annular groove 42 permanently to the part 17 of the stepped bore situated insidathe control piston and hence to the return. The control edge bounding the end face 22 bears the reference numeral 45.

The control edges bounding;the annular grooves 42 and 43 are designated by42a,42b, 43a and 43b, seen from the bottom 11. A-feed throttle 46 may be installed in front of the pressure connection 13 to adjust certain stroke speeds for example. A small notch 47 in the region of the control edge 45 connects the control chamber 25 to the annular groove 31.

In order to explain the operation, starting from Figure 1, it is first assumed that a turning operation has been initiated by switching the external control valve 28 into the control position "a". Pressure medium then passes through the connection P-B, the feed throttle 46, the pressure connection 13, the annular grooves 33,43 and 32 to the working connection 34 and from there through the conduit 35 into the working chamber 6 so that a pressure can build up there. This pressure is propagated backwards to behind the releasing piston 41 so that this can rift the ball 40 from its seat, as illustrated.The pressure medium displaced on an inward movement of the piston 5 out of the working chamber 7 can therefore flow through the passage 38, the released non-return valve 37, the passage 36, the annular grooves 31 and 42, the transverse bore 44, the part 17, the bore 9, the passage 26, the return connection 27 and the connection A-T backto the storage container30. The pressure atthe pressure connection 13 is propagated via the pressure passage 12 to the active surface of the seat valve 14 but at first cannot open this because it is pressed against its seat by the spring 19 directly and bythespring 20 via the control piston 10 resting on the face 23.Should the seat not be hermetically sealed, small leakages can reach the control chamber 25 but gass.from there throug h the small notch 47 into the annular groove 31 and over the path alreadTdescribed back to the storage container. When the piston.. 5 has reached a dead centre defined by externatcircumstances, a further stroke is not possible. The consequence is a pressure rise in the whole pressuresonducting system, that is to say also in the pressure passage 12. As a result of this pressure rise, the seat valve 14 is lifted from its seat against the force of the springs 19 and 20 so that pressure medium can flow into the control chamber 25. Since the whole cross-sectional area of the control piston 10 is considerably larger than that of the seat valve 14, the control piston now executes its full stroke. On the assumption that a predetermined minimum pressure is necessary for the extension of the piston 5, the seat valve 14 will remain with its rear surface 23 in contact with the end face 22, so that no flow through can take place. In the control position of the control piston 10 which has now been reached (see Figure 2), the pressure medium passes from the pressure connection 13, via the pressure passage 12, the control chamber 25, past the control edge 45 into the annular groove 31 and from there via the passage 36, the automatically opened nonreturn valve 37 and the passage 38 into the working chamber 7, as a result of which the extension of the piston is caused.The pressure medium displaced from the working chamber 6 passes via the conduit 35, the working connection 34, the annular grooves 32 and 42 to the transverse bore 44 and from there over the path now already known back to the storage container. When the piston 5 has executed its full outward stroke, the operator can simply let go of the actuating lever, not illustrated here, of the control valve 28, that the control position "o" is automatically assumed.

Since two-way turn-over ploughs are generally connected through hoses and hoses store pressure through expansion, pressure will still prevail in the system last carrying pressure and particularly in the control chamber 25, and can weaken only through leakages at the control valve 28. Since the pressure loads the whole end face 22 of the control piston 10 and a pressure of 4 to 5 bar for example, is already sufficient to hold the springs 19 and 20 in equilibrium,the control piston 10 will at first retain its position. When pressure has dropped to 60 bar for example, the spring 19 can move the seat valve 14 so that the surface 23 is detached from the end face 22 and the gap 24 is opened. Pressure medium can now flow through the gap 24 and the annular gap 21 representing a throttle into the interior of the control piston 10 and to its back.Since the active surfaces of the control piston 10 are equally large on both sides, an overflow of pressure medium takes place and the control piston 10 is guided towards the seat valve 14 by the spring 20. This guiding takes place until the seat valve 14 is resting on its seat and closes the pressure passage 12. From then on, the end face 22 approaches the face 23 of the seat valve 14, while reducing the gap 24, until the gap 24 is completely closed. From this moment on, a further double stroke can be initiated by means of the control valve.

It is clear that, because of the greater pressure drop, a drop in pressure from 120 barto 60 bar, for exam pte, takes place considerably more quickly than one to 4 bar. It is likewise clear that the flowing over of pressure medium takes place more quickly than a stow sinking of the pressure to 4 bar. Thus the total restoring time can be shortened considerably. The size of the annular gap 21 should be selected depending on the supply stream of pressure medium, while even taking into consideration the notch 47 or a corresponding bypass, a pressure head sufficientto close the seat valve 14 must be able to develop.

Naturally, in cases of doubt for the operator in the example of em bodiment illustrated, there is the possibility of achieving an extremely short return time by actuation of the control valve 28 in the control position "b". This additional operation is generally unwanted, however, and with a return line which is not taken to the tractor via the control valve is not even possible. Apart from the very simple solution illustrated, it is, of course, possible to use a valve member which is mounted completely separate from the control piston, in which case the constricted connection then needs a special conduit In such a case, the connection will be opened in the absence of pressure actuation, because a mechanical closing by the control piston does not then take place.

Claims (6)

1. Ahydraulicturning mechanism for a two-way turn-over plough which can be attached to a tractor, having a double-acting piston-and-cylinder unit and a reversing device with a) a housing b) connections in the housing, namely b1) a working connection for a first working chamber of the piston-and-cylinder unit, b2) a working connection for a second working chamber of the piston-and-cylinder unit, b3) a pressure connection which can be connected to at least one pressure medium source through an external control valve, b4) a return connection which is or can be connected to a storage container or intermediate reservoir, c) a control piston in the manner of a 4/2-way valve piston which is adapted for sliding in the housing, comprises two control positions and is permanently loaded by a return spring in the direction of one of the control positions, d) a first active surface on the control piston which is permanently acted upon by the pressure of the pressure medium source, is directed counter two the return spring and is small in comparison with the total cross-section of the control piston, e) a connection, which is opened after a predetermined travel of the control piston, between the pressure connection and a control chamber bounded by a second active surface on the control piston which is likewise directed counter to the return spring and is large in comparison with the total cross-section of the control piston, characterised in that f) there is a flow path (gaps 21 and 24), which can be controlled by a valve member (seat valve 14), between the control chamber (25) and the return, g) which even when the valve member (seat valve 14) is fully open contains at least one constriction (gap 21), h) the valve member (seat valve 14) being permanently loaded by a spring (19) acting in the sense of opening the flow path, i) and opening after the predetermined travel of the control piston (10) below a specific pressure drop between control chamber (25) and return or below a specific pressure in the control chamber (25) and closing above the specific pressure drop or the specific pressure.

2. Ahydraulicturning mechanism as claimed in claim 1, having a control piston, a) which is penetrated through by a stepped bore, b) of which the part having the larger diameter is connected to the return and serves as a spring guide and c) of which the part having the smaller diameter serves as a guide for the stem of a seat valve which is mounted at the end on the control piston and represents the smaller active surface and which opens or closes a connection between a pressure passage leading centrally into the control chamber limited at the end by the control piston and the control chamber, characterised in that d) the seat valve (14) can make a smafi axially directed relative movement in relation to the control piston (10) and e) with the control piston (10) forms a second valve seat which opens or closes the flow path representing the constricted connection (gaps 21 and 24) between the control chamber (25) and the' part (17) having the larger diameter of the stepped bore, f) the stem (15) being provided with a spring washer (18) orthe like on which there rests a first spring (19) determining the predetermined pressure drop and loading the stem (15) in the sense of an opened connection, g) while a second return spring (20), which, together with the first (19) determines the opening pressure between pressure passage (12) and control chamber (25), loads the control piston (10) directly.

3. Ahydraulicturning mechanism as claimed in claim 2, characterised in that the constricted ccsnnec- tion is caused bythe annular gap (21 ) between the stem (15) and the part (16) of the stepped bore having a smaller diameter which guides it

4. Ahydraulicturning mechanism as claimed in one or more of the preceding claims, characterised in that a feed throttle (46) is provided which, with the constricted connection (gaps 21 and 24), forms a cascade connection in such a mannerthatwithfull operating pressure in front of the feed throttle (46), this allows through a stream of pressure medium sufficientto close the constricted connection (gaps 21 and 24).

5. A hydraulic turning mechanism as.cRaimed in one or more of the preceding claims, cha-racterised in that the predetermined pressure drop is some- what less than the lowest pressure occurring in one of the working chambers (6 or7) duringtheturning of the plough.

6. Ahydraulicturning mechanismforatwo-way turn-over plough, substantially as hereinbefore described with reference to the accompanying drawings.