GB2242231A - Telescopic cylinders - Google Patents

Abstract

A hydraulic or pneumatic telescopic cylinder incorporates a piston rod (6, 8) at each end of the main cylinder body (4). The piston rods (6, 8) are extendable from and retractable into the main body of the cylinder (4). Each piston is extendable Independently of the other. When both pistons are fully retracted, one con rod (6) telescopically encloses the second piston rod (8). Piston rod (8) may be locked in either a fully extended or a fully retracted position so as to permit the other piston rod (6) to be used In a conventional manner. Retraction of the con rod (8) is effected by supplying pressure fluid through a port (26) leading to a cavity (24), whereby a floating annular piston (22) acts against a stop (28) on the rod (8) to cause its retraction. <IMAGE>

Description

TELESCOPIC CYLINDERS This invention relates to hydraulic cylinder/ piston

units and in particular to hydraulic or pneumatic telescopic cylinders, suitable for use in booms for mobile cranes, elevating platforms or the like.

Known hydraulic cylinders usually have a single piston.

A hydraulic cylinder/piston unit in accordance with the invention includes two pistons, extendable from and retractable into opposite ends of the cylinder. each piston being extendable independently of the other.

The advantage of a cylinder unit in accordance with the invention is that when extra extension is required one of the pistons can be extended and then locked in the extended position, the other piston then being usable in a conventional manner if so desired.

This invention will now be described further by way of example with reference to the accompanying drawings in which:

Figure 1 shows, partly in cross-section, a cylinder according to the invention, in a fully retracted position.

Figure 2 corresponds to figure 1 but shows a first piston rod extended.

Figure 3 corresponds to Figure 1 but shows both pistons fully extended.

Figure 4 shows the cylinder of Figure 1 with the second piston retracting and the first piston extending.

Figure 5 illustrates a boom incorporating the cylinder of Figure 1.

Figure 6 illustrates the boom of Figure 5 in a fully retracted position.

Figure 7 illustrates the boom of Figure 5 with the second piston rod of the cylinder fully extended.

Figure 8 illustrates the boom of Figure 5 fully extended.

2 Figure 9 illustrates the boom of Figure 8 as it is retracted.

Referring to Figure 1, the hydraulic cylinder generally indicated at 2 has a main body 4 which telescopically encloses a first stage piston "rod" 6 in the form of a first cylinder and a second stage piston rod 8. Sealing members 10,101' are provided at either end of the outer surface of cylinder 6, and engage the inner face of main cylinder 4 in order to form a sealed cavity 12 between the main body 4 and the first cylinder 6.

A port 14 is provided for the ingress or egress of hydraulic or pneumatic fluid into the cavity 12. Another port 16 allows the ingress or egress of fluid into the interior 18 of piston rod 6.

Sealing members 20,22 at either end of a head 23, which is attached to the end of the body 4 from which the second piston 8 protrudes, seal an annular cavity 24 in the inner face of the head 23. A port 26 communicates with the annular cavity 24 through a tubular passage 27 and permits the movement of hydraulic or pneumatic fluid into or out of the cavity.

Sealing member 22 is in the form of a floating piston, which abuts a stop bush 28 at the inner end of piston rod 8, when the piston rod 8 is in a fully extended position from the cylinders 4 and 6 (Fig. 3) or when the piston rod 8 is in the course of retracting (Fig.4). As well as providing a reaction point for floating piston 22, stop bush 28 acts as a guide bearing when the rod 8 is moving in the piston rod 6. The stop bush 28 has axial slots to provide free passage of fluid between the bore 18 of piston rod 6 and the main cylinder bore 181 as shown in Fig.2.

The cylinder 2 can be operated in many ways: for example both pistons 6 and 8 can extend from and retract into the cylinder body 4 together, under the influence of hydraulic fluid entering or exiting the interior cavity 18; or one piston rod can be held in 3 place whilst the other piston rod is extended or retracted.

For example, the second stage piston rod 8 may be used to increase the overall length of the hydraulic cylinder body 4, whilst first stage piston rod 6 allows the cylinder to be used as a conventional cylinder. In this case the operation of the cylinder is as described below.

The second stage piston rod 8 is held in place relative to the body 4 by mechanical means (not shown), such as an external pin or the like. Hydraulic fluid is then admitted via port 16 to the interior 18 of the piston rod 6. The annular cavity 12 between the main body 4 and the piston rod 6 is then vented through the port 14, so allowing the piston rod 6 to extend outwardly by the force of the fluid in cavity 18,181 acting against the fixed inner end 30 of the fixed piston 8 and the floating piston 22 (see Figure 2).

The piston rod 6 is subsequently retracted by admitting hydraulic fluid under pressure into the annular cavity 12 via port 14. This acts against the seal 101 to move the piston 6, the hydraulic fluid within the interior 18, 181 of the piston being vented through port 16.

When it is desired to utilise the extra length of second stage piston rod 8, the mechanical means holding the rod 8 in the retracted position is disengaged. In order to retain the piston 6 in its extended position, port 14 is closed. Hydraulic fluid is then admitted via port 16 to act on piston head 30 and piston 8 extends outward to the position shown in Figure 3. When fully extended the second stage piston 8 may be locked in position by yaechanical means (not shown), port 14 opened and the first stage piston 6 extended out from and retracted into body 4 in a conventional manner, as described, but with the additional extension of piston 8.

When the piston 8 is-to be retracted, the 4 piston 6 is first fully retracted as described above and the annular space 12 formed by the cylinder body 4 and piston rod 6 vented via port 14. Hydraulic fluid is then admitted via port 26 into the annular space 24 in the head 23 and into a further cavity 32 formed between cylinder body 4, piston 8 and the floating piston 22. This causes the floating piston 22 to push against the stop 28 at the inner end of the piston 8, causing the piston to move within the body 4 (See Figure 4). At the same time piston 6 is extended by the floating piston 22 engaging the seal 101 on the inner end of the piston 6, the port 14 being vented.

When piston rod 8 is fully retracted (piston rod 6 fully extended) piston rod 8 is mechanically locked in the retracted position. To complete the operation, hydraulic fluid is admitted via port 14 to the annular space 12 and at the same time ports 16 and 26 are vented allowing the first stage piston rod 6 to retract, at the same time pushing the floating piston 22 back to its start position. The first stage is then ready for use as with a conventional cylinder.

Such a cylinder may be used in many ways, but will now be described by way of example as part of a boom for a lifting device, such as a crane.

Figure 5 shows a boom having four telescopic sections 32,34,36,38. A conventional hydraulic piston/cylinder 40, 401 is provided between the first and second sections 32,34 of the boom, in order to retract and extend the second section 34 into and out of the first section 32.

A second hydraulic cylinder 42 is also provided. However, this cylinder is a two-stage telescopic cylinder in accordance with the invention as previously described by way of example. The first stage piston 4.4 of this cylinder is connected to the second section 34 of the boom, the main body 46 is connected to the third section 36 of the boom and the second stage piston rod 48 is connected by means of a spring coupling 50, to the fourth "fly" section 38 of the boom.

The boom may be used in two modes. In the first mode, only three sections 32,34,36 of the boom 30 are used, as shown in Figure 5. The fly section 38 is secured to the third section 36 by means of a pin 52 which engages in a recess provided in the fly section. In this mode, cylinder 42 acts as a conventional one stage cylinder. the first stage piston rod 44 being retractable in the body 46, so controlling the movement of the third section 36 of the boom into and out of the second section 34.

The boom may also be used In a second mode, wherein the fly section 38 is extended to provide a four-section boom (as shown in Figure 8). In order to achieve this, the boom is fully retracted to the position shown in Fig. 6 and the pin 52 disengaged from the recess provided near the outermost end of the fly section 38. The fly section 38 then extends, under the influence of second stage piston rod 48 which is extended from the cylinder 46 in the manner described above with reference to Figure 3, until the pin 52 engages with a recess provided near the inner end of fly section 38 (See Figure 7). The second and third sections of the boom are then extended in the usual manner to provide a four section beam (as shown in Figure 8).

During the lifting of loads 1n four section mode, the load transmitted through the fly section 38 is carried by the pin 52. This is achieved by means of the spring coupling 50. The spring coupling 50 has a pre-load sufficiently high to carry the weight of the fly section 38, without any deflection. When a load is applied, the spring coupling 50 deflects until the fly section retracts against the section pin 52. This means that the load on the slender second stage rod 48 of the two stage cylinder 42 is only that due to the spring pre-load plus the additional compression. The additional compression is small, being only the 6 clearance required for engagement and dis-engagement of the section pin 52. This means that the second stage rod can have a much smaller section with a resultant saving in weight than would otherwise be required.

In order to return to the three section mode, the second and third stages of the boom are fully retracted as described above with reference to Figure 7 and the pin 52 disengaged. The fly section 38 is then retracted using the second stage piston rod 48. As described previously, in relation to the two stage cylinder 42, as the second stage piston rod retracts, first stage piston rod 44 extends so causing the third section 36 of the boom to extend over the fly section 38 as shown in figure 9. When the fly section 38 is fully retracted (and hence the third section 36 fully extended) the section pin 52 is re-engaged, locking the fly section in the fully retracted position. The boom is then fully retracted and may thereafter be used in the three-section mode.

Although the two-stage hydraulic cylinder unit of the invention has been described in relation to a telescopic boom, it may be used in many other embodiments, typically when an extra extension is required.

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Claims (8)

1. A hydraulic cylinder/piston unit including two pistons extendable from and retractable into opposite ends of the cylinder. each piston being extendable independently of the other.

2. A unit as claimed in Claim 1 wherein means are provided to lock one or both of the pistons in its extended position or its retracted position.

3. A unit as claimed in Claim 2 wherein means are provided to lock one or both of the pistons in both their extended and retracted positions.

4. A unit as claimed in claim 1 wherein a sealing member in the form of a floating piston is provided which is positioned between the inner surface of the cylinder and the outer surface of one of the pistons.

5. A unit as claimed in any preceding Claim wherein the pistons are extended and retracted hydraulically or pneumatically.

6. A unit constructed and arranged substantially as hereinbefore described and with reference to Figures 1,2, 3 and 4 of the accompanying drawings.

7. An extendable and retractable boom consisting of at least three telescopically engaging sections incorporating a unit as claimed in any preceding Claim, the pistons being connected to a second or outer section and a fourth or inner section so as to selectively extend or retract the boom.

8. A boom constructed and arranged substantially as hereinbefore described and with reference to Figures 5 to 9 of the accompanying drawings.

f Published 1991 at The Patent Office. Concept House. Cardiff Road. Ne%lpml. Gwent NP9 I RH. Further copies may be obtained from port. NPI 7H7- Printed by Multiplex techriques lid. St MarY Cray. Kent. Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys. New