AU5193101A - A two stage cylinder assembly - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventor: Address for Service: Invention Title: REDMOND GARY AUSTRALIA PTY LTD Keith Geoffrey Batten CULLEN CO., Patent Trade Mark Attorneys, 239 George Street, Brisbane, QId. 4000, Australia.

A TWO STAGE CYLINDER ASSEMBLY Details of Associated Provisional Applications: PQ8763 13 July 2000 The following statement is a full description of this invention, including the best method of performing it known to us: This invention relates to a two stage hydraulic cylinder assembly.

Two stage hydraulic cylinder assemblies typically consist of a cylinder and two pistons. These assemblies have two ports through which hydraulic fluid may be introduced into and removed from them to allow for extension and retraction of the pistons relative to the cylinder. The operation is such that a primary piston is first extended before the secondary piston may be extended relative to the cylinder. Retraction of the pistons occurs in a reverse order to that mentioned for extension.

These types of two stage cylinder assemblies do not allow for selective operation of the pistons in an order other than the sequence of operation mentioned above.

In some equipment where two stage cylinder assemblies are required, two single stage cylinder assemblies are connected to each other to allow the arrangement to be operated as a two stage cylinder assembly.

In such a combination separate control of the piston of each single stage assembly is possible. However, such an arrangement is S•cumbersome and is not particularly compact.

Cranes employed for erecting utility poles have a multistage boom and because these cranes are required to function near live electric cables it is usual for the final stage of the boom to be constructed of an electrically non-conducting material.

For safe operation of these cranes it is important that the final *stage be extended separately from the extension of the initial stage so that the operator may maximise the extension of the insulated boom when working around live conductors. Known two stage cylinder assemblies are unsuitable for use with such cranes either because they are cumbersome and not compact enough or because they do not allow for selective preparation of the pistons of the two stages.

It is an object of the present invention to provide a two stage cylinder assembly which at least minimises the disadvantages mentioned above.

According to one aspect of the invention there is provided a two stage cylinder assembly having a main housing, a first piston received by the main housing, a second piston received within the first piston, a first port for directing fluid into and from the assembly, a second port for directing fluid into and from the assembly and a third port extending into the assembly for directing fluid into and from the assembly and a control circuit operable to selectively allow fluid to enter the assembly via the first port and exit from the third port to cause the first piston to extend allow fluid to enter the assembly via the first port and exit from the second port to extend the second piston and the circuit being operable when the pistons are extended to selectively allow fluid to enter the assembly via the third port and out the first port to retract the first piston and allow fluid to enter the assembly via the second port and exit via the first port to retract the second piston.

A particular preferred embodiment of the invention will now be described by way of example with reference to the drawings in which: *-jFigure 1 is a perspective view of a two stage hydraulic cylinder assembly according to an embodiment of the invention; Figure 2 is an exploded view of the assembly shown in figure 1; Figure 3 is a detailed partially sectioned longitudinal view of the assembly of figure 1; Figure 4 is a longitudinally sectioned view of the assembly of figure 1; Figure 5 is an hydraulic circuit diagram of an hydraulic circuit for controlling the assembly of figure 1.

Figure 1 shows a perspective view of a two stage hydraulic cylinder assembly 10 according to an embodiment of the invention. A hydraulic control manifold 11 is secured to one end of the assembly 10. A first piston 12 projects outwardly from a cylinder or housing 17 and has fitting 14 for connection to a part of a boom (not shown) of a crane or the like which is operated by the assembly 10. A second piston 15 is received within the first piston 12 and extends beyond the first piston 12 and terminates in a fitting 16 which may be coupled to a boom extension (not shown) of a crane or the like. The assembly 10 has a main housing 17.

Figure 2 shows an exploded view of the hydraulic cylinder assembly 10 of figure 1. The assembly 10 has a main housing 17 with the manifold 11 connected to one end and an end cap 20 coupled to its other end.

The first piston 12 is received within the housing and is moveable within that housing between an extended and a retracted position. The second piston is received within the first piston 12 and is moveable relative to the first piston between an extended and a retracted position.

Figure 3 is a longitudinal partially sectioned view of the assembly 10 of figure 1. The assembly 10 has the manifold 11 fixed at one end of the main housing 17 and the first piston 12 is received within the housing 17 and has an end which projects from the housing 17 and which carries the fitting 14. The second piston 15 is received within the first piston 12. The piston 15 extends beyond piston 12 and carries an end fitting 16 on its free end.

The assembly 10 has ports A, B and C for hydraulic fluid. Port A communicates with chamber 30 adjacent an inner end of the piston 12 and with a chamber 32 adjacent an inner end of the piston 15 via a longitudinally extending passage 31. Port B communicates with a centrally located chamber 33 and with chamber 35 via radial passage 34 and via annular passage 36. Port C extend radially through the main housing 17 and communicates with annular chamber 37.

In operation of the hydraulic cylinder assembly 10, it is possible to extend or retract the first piston 12 without operating the second piston It is also possible to extend or retract the second piston 15 without operating the first piston 12.

""*The first piston 12 may be extended by introducing hydraulic fluid under pressure into port A and by allowing fluid to exit the assembly via port C. Alternatively, the first piston may be retracted by introducing fluid under pressure into the assembly 10 via port C and by allowing fluid to exit from port A. The second piston 15 may be extended by introducing hydraulic fluid under pressure through port A and allowing fluid to exit via port B.

Alternatively, the second piston 15 may be retracted by introducing fluid under pressure into the assembly 10 via port B and allowing fluid to exit from the assembly via port A.

Further details of the assembly will now be described with reference to figure 3 of the drawings. The numerals 38, 39 and 40 denote O rings carried by the manifold 11. A wear ring 41 is carried by the first piston 12 and is located between that piston and the main housing 17. A seal 42 is carried by the first piston 12 and seals that piston against the inner surface of the main housing 17. The assembly 10 has two coaxially extending inner sleeves 43 and 44. These sleeves are separated from each other by a plastic sleeve 45 which acts as a bearing between the two sleeves 43 and 44.

Sleeve 43 is fixed relative to the manifold 11 whilst sleeve 44 is fixed to the first piston 12 and moves with that piston.

A seal 46 is carried by the first piston 12 and that seal seals against sleeve 43 as the piston 12 moves between its extended and retracted positions. The piston 12 carried wear rings 47 at a location immediately S: adjacent the seal 46.

.0•O*0 0 The main housing 17 carries an end cap 20. This end cap 0.00 carries an O ring seal 48 and the O ring seal 48 is captured between the 0 housing 17 and the end cap 20. The end cap 20 has three wear rings 49 located at spaced locations along its length and these wear rings 49 contact an outer surface of the first piston 12. The distal end of the end cap receives a piston wiper 50. A seal 51 is received by the end cap 20 and is located between 2 adjacent wear rings 49.

The fitting 14 carried by the distal end of the first piston 12 carries an O ring seal 52. The second piston 15 is received within the first 0piston 12 and extends into piston 12 and through fitting 14. Three wear rings 53 are located at spaced locations along the fitting 14 and separate that fitting from the second piston 15. A seal 54 is located between two adjacent wear rings 53 and seals against the outer surface of the second piston 15. A wiper is present at the distal end of the fitting 14 and bears against the second piston 15. The end fitting 16 carries a collar 56 and a seal 57 is located at the end of the second piston 15 and between that piston and the fitting 16.

Figure 5 is a view of a hydraulic circuit diagram employed for controlling the assembly 10 of the invention. The broken outline border appearing in this figure is representative of the manifold 11 which forms part of the assembly 10 of the invention. Ports G1, G2, G3 and G4 are test points to which pressure gauges may be attached. In the production version of the assembly, these ports need not be used and may omitted or closed off with suitable plugs.

Valves 60 and 63 in figure 5 are pressure relieving valves which function to return hydraulic fluid from inlets B and C of the assembly 10 via line 66 to the port B shown at the lower part of the diagram and to a reservoir associated with that port. This occurs in the event that a pre-determined pressure in lines 61 and 62 is exceeded.

Valves 64 and 65 function as load holding valves which hold the pistons 12 and 15 in a particular position in the event of an hydraulic failure.

Inlets Al and A2 together allow fluid under pressure to be supplied via line 67 to port A associated with the assembly 10. Valves 64 and 65 each include a non-return valve 64a and 65a. When fluid pressure is applied to inlets Al and .OI..i A2, non-return valve 64a allows that fluid to communicate with port A of the assembly 10 via line 67. This pressure controls valve 65 via line 68 to cause valve 65 to open.

Inputs P1 and P2 are pilot inputs. Fluid under pressure applied to pilot input P1 causes poppet valve 70 to open. When valve 70 opens, nonreturn valve 71 allows a small quantity of fluid to be vented from valve 70 to input P2 via line 72. With valve 70 in its open position fluid supplied via inlet B may be supplied to port B of the assembly 10. Fluid under pressure applied to pilot input P2 causes poppet valve 73 to open and line 74 allows a small quantity of fluid from one side of the valve 73 to vent via line 74 and nonreturn valve 75 via pilot input P1. When valve 73 is open, fluid supplied from manifold inlet B via valve 65 is supplied to port C of the assembly 10 via line 62 and valve 73. Thus, pilot inputs P1 and P2 control the poppet valves and 73 respectively to allow hydraulic fluid under pressure to be directed either to port B or port C of the assembly Figure 4 is a longitudinally sectioned view of the assembly of figure 3. Like numerals t that used in figure 3 appear on figure The assembly of the invention together with its associated hydraulic control circuit functions to provide for independent control of the first and second pistons 12 and 15 such that these pistons may be individually extended and retracted.

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Claims (13)

1. A two stage cylinder assembly having a main housing, a first piston received by one main housing, a second piston received within the first piston, a first port for directing fluid into and from the assembly, a second port for directing fluid into and from the assembly and a third port extending into the assembly for directing fluid into and from the assembly and a control circuit operable to selectively allow fluid to enter the assembly via the first port and exit from the third port to extend the first piston to extend allow fluid to enter the assembly via the first port and exit from the second port to extend the second piston and the circuit being operable when the pistons are extended to selectively allow fluid to enter the assembly via the third port and out the first port to retract the first piston and allow fluid to enter the assembly via the second port and exit via the first port to retract the second piston.

2. The assembly of claim 1 wherein the first port extends into an end of the housing at a location near an inner end of the housing and communicates with a chamber near the inner end of the first piston and via a longitudinal •passage with a chamber adjacent an inner end of the second piston.

3. The assembly of claim 1 or 2 wherein the third port extends radially into the housing and communicates with an annular chamber extending about the first piston.

4. The assembly of claim 1, 2 or 3 wherein the second port extends into an end of the housing and communicates with a centrally located chamber extending through and along the pistons and with a chamber located within the first piston and between the first and the second pistons via a radial passage and an annular passage.

5. The assembly of any one of claims 1 to 4 including an end cap at a distal end of the housing.

6. The assembly of any one of claims 1 to 5 including a manifold at a proximal end of the housing and the first and the second extend into the manifold.

7. The assembly of any one of claims 1 to 6 wherein the first piston has a fitting at its distal end for connection to a boom of a crane.

8. The assembly of any one of claims 1 to 7 wherein the second piston has a fitting for attachment to a boom extension of a crane.

9. The assembly of any one of claims 1 to 8 wherein the circuit includes a first holding valve for directing fluid to the first port and a second holding valve for directing fluid to the second port.

The assembly of claim 9 including respective pressure relieving valves communicating with the second port and the third port.

11. The assembly of claim 9 or 10 including respective poppet valves coupled to the second port and the third port and controllable by respective pilot valves.

12. A two stage cylinder assembly substantially as herein described with reference to the drawings. DATED this

13 June 2001 Redmond Gary Australia Pty Ltd By their Patent Attorneys CULLEN CO. l* l* i li lo* l