GB2287989A - Hydraulic circuit for a stone grab - Google Patents

Abstract

Apparatus for controlling two linear motors, in particular hydraulic cylinders (1, 2) of a stone grab which are interconnected through a connection passage (9) connected to the piston chamber (8) of the first cylinder (1) and to the annulus (10) of the second cylinder (2), the piston surface (11) of the first cylinder (1) and the annular surface (12) of the second cylinder (2) being substantially equal in area to provide for synchronous operation of the piston rods (13, 14) at the time of extension and retraction thereof, comprising two supply passages (4, 5), one connecting a pressure medium tank to the annulus (6) of the first cylinder (1) and the other one connecting said pressure medium tank to the piston chamber (7) of the second cylinder (2), a check valve (15) arranged within said first supply passage (4), a controllable pressure regulator (50) arranged between said two supply passages (4, 5) to control the closing pressure of the cylinders (1, 2) a pressure reversing valve (17) arranged between said two supply passages (4, 5) and operated as a pressure regulator, and at least one pump provided on the boom of a crane, for feeding the pressure medium, wherein the pressure reversing valve (17) is connected through a control passage (20) to a directional valve (18) which through to a working passage (18') is connected to the first supply passage (4) and is loaded with pressure medium through said passage. <IMAGE>

Description

Apparatus for Controlling two Linear Motors, in particular Hydraulic Cylinders This invention relates to an apparatus for controlling two linear motors, in particular hydraulic cylinders of a grab, preferably a stone grab, which are interconnected through a connection passage connected to the piston chamber of the first cylinder and to the annulus of the second cylinder, the piston surface of said first cylinder and the annular surface of said second cylinder being substantially equal in area so as to provide for synchronous operation of the piston rods at the time of extension and retraction thereof, said apparatus comprising two supply passages, one thereof connecting a pressure medium tank to the annulus of said first cylinder and the other one connecting said pressure medium tank to the piston chamber of said second cylinder, a check valve provided within said first supply passage, a controllable pressure regulator provided between said two supply passages for controlling the closing pressure of said cylinders, a pressure reversing valve provided between said two supply passages and performed as a pressure regulator, and at least one pump for feeding said pressure medium, said pump being usually externally arranged on a crane of a truck or the like, resulting in that hydraulic medium is supplied to said hydraulic cylinders through the hydraulic system inherent to the truck.

From prior art, e.g. DE-GM 91 04 137.6, grabs and preferably stone grabs are known having grab arms which are guided to be mutually parallel displaceable in a central carrying piece provided with coupling means through legs angularly connected thereto, and having a hydraulic piston-cylinder unit moving said grab arms toward and away from each other.A grab of this known type comprises two mutually parallel piston-cylinder units, the cylinders thereof being each connected to one grab arm on mutually opposite end portions of the carrying piece and piston rods, the closed end of said one cylinder and the exit of the piston rod of said other cylinder being connected to the pressure and return passages respectively for the hydraulic liquid, the other closed end and the other exit of the piston rod of the cylinders being interconnected through a connection passage, and the cross sectional surface of the annulus of the cylinder chamber of said one cylinder connected to the connection passage being substantially corresponding to the cross-sectional surface of the cylinder chamber connected to the connection passage which is free of the piston rod.

Such types of grabs with their hydraulic system configured as described above, have proven worthwhile especially as stone grabs, since with such a grab the two cylinders operative to open and close the grab arms are interconnected through a connection passage in a manner such as to ensure the required synchronous operation of the grab arms. To this end, the two cylinder chambers interconnected through the connection passage have equal cross-sectional surfaces, this being attained by a correspondingly smaller diameter of the cylinder having its closed end joined by the connection passage.Since the hydraulic liquid respectively displaced from a cylinder chamber is supplied to the other cylinder by means of the hydraulic connection passage, the pistons of both cylinders are interconnected so to speak by hydraulic rods such that due to the equal cross-sectional surfaces of the cylinder chambers interconnected by the connection passage they travel in the mutually opposite direction by an equal amount. Said opposite coupling of the cylinders allows ample opening and closing motions to be carried out at small piston strokes, the grab as a whole being performed very robust, because the opening and closing forces are generated purely hydraulically.

Moreover, said opposite coupling of the cylinders offers the advantage of obtaining symmetrical opening and closing motions of the grab arms.

For controlling the opening and closing motions of the grab arms of such grabs apparatus of the aforementioned type are pre known. One such control apparatus is represented, for example, in Figure 4.

This control apparatus, which is adapted to control two hydraulic cylinders 21 and 22 of a stone grab, consists of a control block 23 comprising two supply passages 24 and 25 by means of which said hydraulic cylinders 21 and 22 are connected to a pressure medium tank not shown in the drawings.

Supply passage 24 is connected to the annulus 26 of hydraulic cylinder 21 and supply passage 25 is connected to the piston chamber 27 of hydraulic cylinder 22. To piston chamber 28 of the hydraulic cylinder 21 there is con nected a connection passage 29 which is connected by its second end to the annulus 30 of hydraulic cylinder 22.

With the control apparatus as shown, the piston surface 31 is equal in area to the annular surface 32 of the hydraulic cylinder 22 so as to ensure synchronous operation of the piston rod 33 of hydraulic cylinder 21 and the piston rod 34 of hydraulic cylinder 22 at the time of extension and retraction thereof.

Within control block 23 there is inserted in supply passage 24 a hydraulically unlocking check valve 35 connected through a passage 36 to the supply passage 25. Moreover, control block 23 has three internally pilot-operated pressure relief valves 37, 38 and 39 in cartridge configuration. To this end, the pressure relief valve 37 is arranged in a passage 40 interconnecting the supply passages 24 and 25 and serves for the reversing of pressure. To this end, the pressure relief valve 37 is connected by its input side to a ball valve 41 arranged extemally of control block 23, said ball valve being adapted for mechanical or manual operation and being connected by its input side to supply passage 24. The pressure relief valve 37 is controlled through a control passage 42 connected to passage 40.

The remaining two pressure relief valves 38 and 39 serve for opening and closing respectively for extending and retracting the piston rods 33 and 34 of the hydraulic cylinders 21 and 22. To this end, the pressure relief valve 38 which serves for extending and retracting said piston rods 33 and 34 is interposed in a passage 43 provided between the supply passages 24 and 25, said pressure relief valve 38 being connected by its input side to the supply passage 25 which in this case represents the return passage to the pressure medium tank (not shown). On the other hand, the pressure relief valve 39 is arranged in a passage 44 also interconnecting said supply passages 24 and 25, however, said pressure relief valve 39 being connected by its input side to the supply passage 24 supplying pressure medium withdrawn from the pressure medium tank (not shown) to the annulus 26 of the hydraulic cylinder 21 through a pump (not shown).

Both the pressure relief valve 38 and the pressure relief valve 39 have respective control passages 45 and 46 connected to their corresponding pas sage 43 and 44 on the input side of the pressure relief valve 38 respectively 39.

The above-described control apparatus has proven worthwhile as a positive control for controlling two hydraulic cylinders of a stone grab.

Basing on this prior art, it is an o b j e c t of the invention to perform an apparatus of the type concerned used for controlling two linear motors and in particular two hydraulic-cylinders of a grab, preferably a stone grab, in a manner such that its structure is simple and easy to manufacture and particularly provides for a reliable and simple control with the desired synchronism of the piston rods at the time of extension and retraction thereof, especially low pressures or volume flow being required for valve control.

With an apparatus of the type concerned this object is so I v e d by the pressure reversing valve being connected through a control passage to a directional valve which is connected through a working passage to the first supply passage and is charged by the pressure medium through said passage.

An alternative so I u t i o n of this object provides that a directional control valve is arranged between both supply passages, said valve being adapted to be controlled through a control passage, that the control passage is connected to the directional valve on the input side thereof, which on its output side is connected to a pressure regulator through a control passage which in turn is connected to said supply passage by an output-side control passage, and that between said control passage and said directional valve and said output-side control passage of the pressure regulator there is arranged a second pressure regulator which on the output side thereof is connected to the control passage of the first pressure regulator.

Apparatus for controlling two linear motors, in particular hydraulic cylinders of a grab and preferably a stone grab, which are performed as described above, particularly offer the advantage that by the arrangement of a directional valve there can be saved a pilot-operated pressure relief valve, the structure of the control apparatus being simplified to an extent which allows such control apparatus to be manufactured at low cost. In addition, by these constructions the mechanically and/or manually operated ball valve is replaced by the directional valve which offers improved operation characteristics as compared to a ball valve.Thus the pressure reversing valve can be controlled in a simple and advantageous manner through the control passage with a low pressure and volume flow respectively which is produced in the directional valve, the working pressure of the control apparatus being present in the directional valve.

Moreover, compared to prior art, the above-described apparatus for controlling two linear motors, in particular hydraulic cylinders of a grab and preferably a stone grab, offer the advantage of preventing operation errors. In contrary to prior art apparatus equipped with a ball valve, reversing takes place compulsory in the apparatus according to the invention, whereas the ball valve in prior art apparatus, although opening compulsory, does not close compulsory which means a disadvantage as compared to the apparatus according to the present invention. Accordingly, the ball valve allowed the hydraulic cylinder to be operated at a low pressure only at the time of retraction thereof. In addition, with the apparatus according to the invention, pressure regulation is independent from the feed flow of a pump.Compared thereto, it is a disadvantage of prior art that the entire volume flow passes over the ball valve whereby the resulting stagnant pressures take influence on the pressure relief valve 37 (Figure 4). Finally, it can be seen that any pressure regulation for the extension of the hydraulic cylinders may be dropped with the apparatus according to the invention.

For the directional valve arranged between the two supply passages there is preferably selected a 2/2-directional valve, the (second) directional valve being controllable from outside.

For using the apparatus according to the invention for the control of two linear motors in stone grabs having height-adjustable clamping jaws it has proven expedient if the (second) directional valve is controllable through a height-adjustable clamping jaw, for example of a stone grab, in such a manner that a lower working pressure is prevailing when the clamping jaw is in its extended position and that a higher working pressure is prevailing when the clamping jaw is in its retracted position to thereby prevent the stone grab from being damaged by excessive working pressures when the clamping jaw is in its extended position.

A further feature of the invention provides that the directional valve has a tappet which is arranged inside of a shaft of the clamping jaw and can be operated through a carrier or similar means supported to be displaceable within the shaft. A particular advantage offered by this construction is that the (second) directional valve is arranged within a metal construction so as to be substantially protected against damages which are always caused by the stone grab being swivelled, for example, against an obstacle whereby the (second) directional valve gets damaged or destroyed.To this end, it has proven to be an advantage if the tappet carries a plate arranged under an angle, said plate being arranged so that the carrier guided in said shaft hits the plate by its free end when the clamping jaw is retracted and pushes said plate together with the tappet into the directional valve so that the latter is switched from low working pressure to high working pressure.

With the above-described apparatus it has turned out to be an advantage if the check valve is performed to be unlocking, said check valve being connected to the two supply passages through control passages and having at least one control passage and a choke in series with the check valve. By this construction lower pressures than those in prior art are required for controlling the check valve. The same applies to the control of the pressure reversing valve which also only requires a low pressure. This is attained by the pressure reversing valve being driven through the directional valve.

Finally, it has proven to be an advantage if there is interposed in the connection passage a pressure measuring device, preferably a manometer, indicating the pressure decisive for the mode of operation of the stone grab in order to indicate its carrying capacity in the hydraulic system.

In the following, there will be described in conjunction with Figure 1 one embodiment of the apparatus according to the invention for controlling two linear motors, in particular hydraulic cylinders of a stone grab.

The apparatus shown in Figure 1 comprises two hydraulic cylinders 1 and 2 as well as a control block 3. Via control block 3 two supply passages 4 and 5 are connected to the hydraulic cylinders 1 and 2. Supply passage 4, which on its input side is connected to a pressure medium tank through a pump not shown, is connected to the annulus 6 of hydraulic cylinder 1, and supply passage 5, which is also connected to the pressure medium tank, is connected to the piston chamber 7 of hydraulic cylinder 2. The piston chamber 8 of hydraulic cylinder 1 is connected through a connection passage 9 to the annulus 10 of hydraulic cylinder 2, the piston surface 11 of hydraulic cylinder 1 being equal in area to the annular surface 12 of hydraulic cylinder 2 whereby synchronous operation of the piston rods 13 and 14 is guaranteed at the time of retraction and extension thereof.

In supply passage 4 there is interposed a hydraulically unlocking check valve 15 which is connected through a control passage 16 to the supply passage 5 and through a control passage 16' to the supply passage 4 on the input side thereof, said control passage 16' having a choke 16".

Moreover, in control block 3 there is arranged a pressure reversing valve 17 which is performed as a pressure regulator and is connected on its input side to supply passage 4 through a passage 19. On its output side said pressure reversing valve 17 is connected through a passage 19' to the supply passage 5. The pressure reversing valve is driven through a control passage 20 which with its opposing end is connected to a directional valve 18, said directional valve being a 2/2-directional valve. Directional valve 18 in turn is connected on its input side to the supply passage 4 through a working passage 18'.

Accordingly, the pressure reversing valve 17 is driven in response to the position of the directional valve 18, the pressure of the pressure medium available in the working passage 18' being changed to a lower pressure required for driving the pressure reversing valve 17 through control passage 20 so that not the entire pressure medium flow of the supply passage 4 is required for the control of the pressure reversing valve 17.

Finally, control block 3 has an internally pilot-controlled pressure regulator 50 interposed in a passage 51 interconnecting supply passages 4 and 5, said pressure regulator 50 having a control passage 52 which is connected on the input side of the pressure regulator 50 to passage 51.

In connection passage 9, which interconnects the piston chamber 8 of hydraulic cylinder 1 and the annulus 10 of hydraulic cylinder 2, there is interposed a manometer 9' through a branch passage 9". Said manometer 9' serves for indicating the pressure available in the connection passage which is representative of the pressure available in the hydraulic system.

In Figure 2, there is shown a second embodiment of the apparatus according to the invention for controlling two hydraulic cylinders 1 and 2. Other than the first embodiment represented in Figure 1, the second embodiment shown in Figure 2 includes a 2/2-directional valve 53 which is arranged between said two supply passages 4 and 5 and can be driven through a control passage 54. With this 2/2-directional valve both hydraulic cylinders 1 and 2 are driven so that both of them either extend or retract their piston rods 13 and 14. Driving of the 2/2-directional valve 53 is effected through control passage 54 which is connected to the input side of a directional valve 18 which on its output side is connected through a control passage 55 to a pressure regulator 56.The directional valve 18 can be switched by means of a tappet with a plate 59, the operation thereof still to be described in more detail in the following.

The pressure regulator 56 in turn is connected on its output side through a control passage 57 to the supply passage 5, wherein between the control passage 54, which connects the control side of the 2/2-directional valve to directional valve 18, and the control passage 57 there is arranged a second pressure regulator 58 which is connected on its output side to the control passage 57 of the first pressure regulator 56.

The above-described embodiments of the apparatus for controlling said hydraulic cylinders 1 and 2 are especially suited for driving two hydraulic cylinders 1 and 2 of a stone grab 60 such as represented in a lateral view in Figure 3. The stone grab 60 consists of two clamping jaws 61 of substantially the same construction consisting of essentially rectangularly sectioned profiles mutually arranged in U-shape. Moreover, each clamping jaw 61 has a frame 62 arranged to be displaceable in the longitudinal direction of the legs of the U-shaped clamping jaws 61, said frame being also U-shaped so that the two legs thereof are supported to be displaceable within the legs of the clamping jaws 61.Between the two legs of the clamping jaws 61 there is fixed a bracing 63 wherein it is arranged a rail 64 provided between the legs of the frame 62 for height adjustment of frame 62 relative to the clamping jaw 61. On its web 62 arranged between the legs, frame 62 carries a pressure bar 66, preferably made of an elastomer, for engagement with a stack of stone, for example. As can been learnt from Figure 3, the directional valve 18 is arranged in the hollow space of the web 67 of the clamping jaw 61 interconnecting said two legs in a manner such that its tappet with plate 59 projects into the hollow space of said one leg of clamping jaw 61.The plate 59 is arranged on the tappet under an angle such that the leg of frame 62 guided within said leg of the clamping jaw 61 pushes against plate 59 when the frame 62 is in its retracted position and accordingly switches the directional valve 18 so that a higher working pressure is available in the apparatus. There must be distinguished between two working pressures, among which the low pressure exists in the apparatus when frame 62 is extended relative to the clamping jaw so that as a consequence of this low working pressure the contact pressure at which the clamping jaw 61 with pressure bar 66 engages a stack of stone is also low to thereby prevent stone grab 60 from being damaged.

With the apparatus according to the invention for controlling the hydraulic cylinders 1 and 2 the check valve 15 has a maximum open control ratio of 1:3, wherein it has proven to be particularly advantageous if the open control ratio is set 1:2. In addition, the pressure reversing valve 17 has a setting range of up to 215 bar which corresponds to the setting range of the pressure regulator 50. The pressure reversing valve 17 is adapted to be lead sealed, the setting range of the pressure regulator 50 being adjustable by a hand wheel. The maximum rate of flow in the above-described apparatus amounts to 75 I/min and is preferably set to 60 I/min.

Moreover, the supply passages 4 and 5 in the apparatus according to the invention have a different diameter, the diameter of supply passage 4 being in any case greater than that of supply passage 5.

Claims (10)

Claims

1. Apparatus for controlling two linear motors, in particular hydraulic cylinders (1, 2) of a grab, preferably a stone grab, which are interconnected through a connection passage (9) which is connected to the piston chamber (8) of the first cylinder (1) and to the annulus (10) of the second cylinder (2), the piston surface (11) of the first cylinder (1) and the annular surface (12) of the second cylinder (2) being substantially equal in area in order to provide for synchronous operation of the piston rods (13,14) at the time of extension and retraction thereof, comprising two supply passages (4, 5), one thereof connecting a pressure medium tank to the annulus (6) of the first cylinder (1) and the other one thereof connecting said pressure medium tank to the piston chamber (7) of the second cylinder (2), a check valve (15) arranged within said first supply passage (4), a controllable pressure regulator (50) arranged between said two supply passages (4, 5) to control the closing pressure of the cylinders (1, 2), a pressure reversing valve (17) arranged between said two supply passages (4, 5) and performed as a pressure regulator, and at least one pump, preferably provided on the boom of a crane, for feeding the pressure medium, characterized in that the pressure reversing valve (17) is connected through a control passage (20) to a directional valve (18) which through a working passage (18') is connected to the first supply passage (4) and is loaded with pressure medium through said passage.

2. Apparatus for controlling two linear motors, in particular hydraulic cylinders (1, 2) of a grab, preferably a stone grab, which are interconnected through a connection passage (9) which is connected to the piston chamber (8) of the first cylinder (1) and to the annulus (10) of the second cylinder (2), the piston surface (11) of the first cylinder (1) and the annular surface (12) of the second cylinder (2) being substantially equal in area in order to provide for synchronous operation of the piston rods (13, 14) at the time of extension and retraction thereof1 comprising two supply passages (4, 5), one thereof connecting a pressure medium tank (5') to the annulus (6) of the first cylinder (1) and the other one thereof connecting said pressure medium tank (5') to the piston chamber (7) of the second cylinder (2), a check valve (15) arranged within said first supply passage (4), and at least one pump, preferably provided on the boom of a crane, for feeding the pressure medium, characterized in that between said two supply passages (4, 5) there is ar ranged a directional valve (53) adapted to be driven through a control passage (54), that the control passage (54) is connected to a second directional valve (18) on the input side thereof which on the output side thereof is connected through a control passage (55) to a pressure regulator (56) which in turn is connected by an output-side control passage (57) to the supply passage (5) and that between said control passage (54) of the second directional valve (18) and the control passage (57) of the pressure regulator (56) there is provided a second pressure regulator (58) which is connected on the output side to the control passage (57) of the first pressure regulator (56).

3. Apparatus according to claim 1 or 2, characterized in that the check valve (15) is performed as an unlocking check valve, said check valve (15) being connected through control passages (16,16') to said two supply passages (4, 5) and at least having one control passage (16') and a choke (16") in series with said check valve (15).

4. Apparatus according to claim 1 or 2, characterized in that the connection passage (9) has a pressure measuring device (9').

5. Apparatus according to claim 2, characterized in that the directional valve (59) is performed as a 2/2-directional valve.

6. Apparatus according to claim 1 or 2, characterized in that the directional valve (18) is controllable from outside.

7. Apparatus according to claim 6, characterized in that the directional valve (18) is adapted to be driven through a height-adjustable clamping jaw (61), for example of a stone grab (60), in a manner such that a low working pressure exists with the clamping jaw (61) in its extended position and that a high working pressure exists with the clamping jaw (61) in its retracted position.

8. Apparatus according to claim 7, characterized in that the directional valve (18) has a tappet which is arranged within a profile of the clamping jaw (61) and is adapted to be operated through a frame (62) or similar means displaceable arranged and supported within said profile.

9. Apparatus according to claim 8, characterized in that the tappet carries a plate (59) arranged under an angle.

10. Apparatus constructed arranged and adapted to operate substantially as hereinbefore described with reference to the accompanying drawings.