GB2128680A

GB2128680A - Hydraulic cylinder and piston

Info

Publication number: GB2128680A
Application number: GB08228851A
Authority: GB
Inventors: Anthony James Duthie
Original assignee: JOHNSTON BROTHERS
Current assignee: JOHNSTON BROTHERS
Priority date: 1982-10-08
Filing date: 1982-10-08
Publication date: 1984-05-02
Also published as: GB2128680B

Abstract

A hydraulic cylinder (10) has an enlarged diameter portion (17) at one end. A piston (20) slides in the cylinder and has a coaxial bore (22) in which an actuating piston (23) slides. As the piston (20) reaches the end of its travel the actuating piston moves relative to the piston (20) and causes locking balls (40) to engage the enlarged diameter portion of the cylinder bore. When it is desired to unlock the cylinder, fluid is applied to the actuating piston to move it in the opposite direction relative to the piston (20) releasing the balls. <IMAGE>

Description

SPECIFICATION A locking arrangement hydraulic cylinder and piston This invention relates to a hydraulic cylinder and piston which is provided with a means for automatically locking the piston within the cylinder at one end of its travel.

In accordance with the present invention there is provided a hydraulic cylinder, having an enlarged diameter portion adjacent to one end, a piston slidable in the cylinder, a bore formed in and coaxial with the piston, an actuating piston member slidable in an unbiased manner within the bore, at least one locking member associated with the piston and a duct means for suppiying fluid to the bore, the arrangement being such that: when the piston is nearing the enlarged end of the cylinder, the actuating piston member is forced to move in such a way that this actuating piston member causes the locking member to engage the enlarged diameter portion of the cylinder; when fluid pressure is applied via the duct to the actuating piston member, said member is moved by hydraulically applied force in such a way that this actuating piston member causes the locking member to disengage the enlarged diameter position of the cylinder, thus unlocking the piston.

Preferably there is a plurality of locking members. It is preferred that the duct means connects the bore with the face of the piston furthest from the piston rod, and that a force is applied to the end of the actuating piston member furthest from the piston rod, to urge the actuating piston member in the direction of the piston rod, to cause the locking member to engage the enlarged diameter portion of the cylinder if the piston is adjacent to said portion.

The force applied to the end of the actuating piston member furthest from the piston rod may be due to hydraulic pressure within the cylinder acting on said end of the actuating piston member.

Alternatively there may be a pin, which is fixed to the actuating piston member, protruding along said duct, such that a force applied to the free end of said pin will be transmitted to said end of the actuating piston member.

The pressure on the pin that causes the locking may be hydraulic pressure from within the cylinder. Alternatively the pressure on the pin that causes locking may be caused by mechanical contact of the free end of the pin with the end of the cylinder as the piston approaches said end of the cylinder.

Preferably the locking members are balls within generally circular ports, said ports connecting the bore within the piston to the cylindrical surface of the piston.

It is preferred that the actuating piston member has a tapered portion, such that movement of the actuating piston member in the bore will cause the balls to roll along the tapered portion and thus protrude from the piston side.

Alternatively, the actuating piston member may have two tapered portions arranged to define a groove around said actuating member, such that movement of the actuating piston member in the bore will cause the balls to roll out of the groove and so protrude from the piston side.

The details of embodiments of this invention will be described by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a sectional view of a cylinder and piston, and a diagrammatic representation of a hydraulic control circuit for the cylinder; and Figure 2 shows a sectional view of another arrangement of the cylinder and piston of this invention.

A cylinder, within which is a piston driven by a hydraulic fluid, may be used for raising and lowering equipment, e.g. for raising and lowering a brush assembly or a suction nozzle of a road sweeping machine. Within such a cylinder 10, as shown in Figure 1, a latching mechanism is provided to mechanically lock the piston in place within the cylinder and to sustain a load such as a brush assembly when the cylinder is in its "retracted" state, which would for example, correspond to the position in which any attached equipment were in a raised state.

The cylinder 10, within which is a piston 20, has an internal cylindrical bore 18 running from end wall 14 toward end wall 11, which extends along the majority of the length of the cylinder.

Toward end wall 11 however, the bore diameter gradually increases to form a section 17 of the bore, this portion being conical in shape and coaxial to bore 18. Between end wall 11 and section 1 7 is a section 1 6 of the bore, which is of uniform diameter, but of a larger diameter than section 1 8. The section 1 7 thus provides a smooth transition between the two diameters of bore, all section of the bore being coaxial.

In the cylindrical wall of cylinder 10, adjacent end wall 11, is a fluid port 13, which connects this end of the cylinder to a hydraulic control circuit 50. Outside the cylinder, attached to end wall 11 is an anchorage 12, which is used to secure this end of the cylinder to the machine of which the cylinder is a part.

The other end wall 14 is provided with a hole, coaxial with the cylinder through which passes a piston rod 30. Adjacent to end wall 14, the cylindrical wall of the cylinder contains a port 15, which connects this end of the cylinder to the hydraulic control circuit 50.

Piston 20 is attached at one end 24 to a piston rod 30. Into the other end 25 of the piston has been driven a bore 22, which bore is cylindrical and coaxial with the piston and the piston rod.

There are six holes 28, from the bore 22 to the outer cylindrical surface 29 of the piston. The holes are equidistant from the end 25 of the piston, and are spaced symmetrically around the axis of the piston. Within each hole 28 is a steel ball 40.

Within the bore 22 is a cylindrical slug 23, with a diameter only sightly less than the internal diameter of bore 22. In the cylindrical surface 26 of the slug 23, towards an end 45 of the slug is formed a V-shaped groove 27, the two sides of which groove are thus conical in shape. This groove is deep enough that, when positioned opposite holes 28, the balls 40 can rest in the groove to be below surface 29 of the cylinder. The slug 23 is slidable along this bore 22, so that the holes 28 may be variously opposite the groove 27 of the cylindrical surface 26 of the slug.

On the end 42 of the slug furthest from the piston rod 30 is a pin 41. Around the inside of the bore 22, near the end 25 of the piston is a circlip 44 to prevent the slug 23 from coming out of the bore.

Piston rod 30 has a coaxial duct 31 running along its entire length, this duct opening at one end into the bore 22. At the other end 32 of the piston rod the duct 31 terminates in port 33, which connects the duct to the hydraulic control circuit 50. Attached to end 32 of the piston rod is an anchorage 34, similar to anchorage 12.

To increase the effectiveness of the hydraulic cylinder, seals 21 are provided around the piston 20, around the slug 23, and also around the inside of the hole in end wall 14 through which the piston rod 30 passes.

A typical hydraulic control circuit 50 comprises a pump 51, a control valve 52, a vent 53 and a hydraulic motor 54 for brush drive with hydraulic lines 55 to 62 between these components and the cylinder. Control valve 52 has three positions 65 to 67 for controlling the apparatus. When the control valve 52 is set in position 65 the hydraulic pressure from the pump 51 is transmitted to hydraulic line 57, and thus into the cylinder 10 via port 1 5. This pressure will thus act against piston 20 to force the piston towards end wall 11. The direction of travel of piston 20 will of course depend on the relative magnitudes of the forces on the piston due to the hydraulic pressure and to any mechanical force transmitted to piston 20 via piston rod 30.The pressure on end 25 of the piston is atmospheric, as port 1 3 is connected to hydraulic line 62 which is permanently connected to the vent 53. Also when control valve 52 is in position 65, hydraulic lines 58, 59 are connected to the vent 53 via line 55. Thus duct 31 is vented to the atmosphere via port 33 and line 58, 59.

When control valve 52 is moved to position 67, hydraulic pressure is applied to line 58 to drive the hydraulic motor as line 59 is connected to line 58 the motor force pressure is applied to duct 31, simultaneously the whole of the cylinder 10 is vented to the atmosphere, via lines 56, 57.

In position 66, both lines 57 and 58 are sealed by the control valve 52, and line 56 is connected to line 55, thus the pump output is vented to atmosphere.

In operation, for the piston to retract and raise the brush assembly, the slug 23 must be positioned so that the groove 27 is opposite the holes 28. The steel balls 40 can thus lie flush with the curved surface 29 of the piston, and so allow the piston to travel unhampered along the cylinder. Control valve 52 will be in position 65.

As the piston 20 approaches end wall 11 the holes 28 are opposite section 1 6 of the cylinder bore. As the piston continues to move towards ends wall 11, a pin 41 will then abut the end wall 11 and force the slug 23 along the bore 22. This movement of the slug 23 will mean that less and less of the groove 27 will be opposite holes 28, and instead the cylindrical surface 26 of the slug will be opposite these holes. Thus the balls 40 will be forced to protrude from the holes, which increases the effective diameter of the piston.

This increased diameter will prevent the piston extending or travelling towards the end wall 14 of the cylinder, as the balls will be confined to section 1 6 of the cylinder bore locking against the conical section 17.

The piston 20 is now effectively locked at this end of the cylinder 10, and no further hydraulic pressure is needed to keep the piston in place.

When valve 52 is moved to position 61, the hydraulic pressure on end 24 of the piston will gradually decay due to leakages, but since the piston 20 is locked in position by the protrusion of balls 40, this will have no effect.

To release the piston 20 from its locked state, the control valve 52 must be moved into position 67. In this position the cylinder is completely vented to the atmosphere but hydraulic pressure is applied to duct 31. This pressure in the duct 31 forces slug 23 towards end 25 of the piston. As the slug moves, the groove 27 is once more aligned opposite the holes 28, allowing the balls 40 to lie flush with cylindrical surface 29 of the piston, rather than protruding from its surface.

When the groove 27 has been aligned with the holes 28 the piston 20 will be free to move, but will not do so until a mechanical force is applied to it via piston rod 30, by way of the weight of the brush assembly. Then as the piston 20 moves, the balls 40 abutting with section 1 7 will be caused to ease deeper into the holes 28, so that they lie within groove 27. As the piston 20 continues to move, the balls 40 will reach the section 18 of the bore of the cylinder, by which time they will be flush with the cylindrical surface 29 of the piston, allowing the piston 20 to pass freely again along the length of the cylinder, until the brush assembly falls and touches the ground where it will be allowed to float freely all the time the hydraulic motor is operating.

In an alternative embodiment, as shown in Figure 2, a cylinder 110 within which is a piston 120 driven by a hydraulic fluid, is again used for raising and lowering equipment as before.

Within the cylinder 110 is a latching mechanism which is provided to mechanically lock the piston in place within the cylinder when the cylinder is in an "extended" state.

The cylinder 110 has an internal cylindrical bore 118 which runs from end wall 170 towards end wall 1 71, and which extend along the majority of the length of the cylinder. Towards end wall 171 is a section 11 7 of the internal bore of the cylinder which has a uniform increase in diameter with increasing distance from end wall 1 70. Thus section 117 of the bore is conical in shape, and is also coaxial to the bore 118 and to the cylinder 110. Between end wall 171 and section 117 is a section 116 of the internal bore of the cylinder, which is also coaxial with the bore 11 8 but is of a larger diameter.The diameter of section 11 7 where this section it meets the bore 118 is the same as that of bore 11 8, and similarly where section 11 7 adjoins section 11 6, the diameter of both of these sections is the same.

The section 117 thus provides a smooth transition between the other two diameters of bore, in a similar manner to section 1 7 in the first embodiment.

In the end wall 170 of the cylinder 110 is an indent 1 72 which is coaxial with the cylinder. This indent 172 is connected by a duct 173 to a fluid port 174, which is connected in turn to a hydraulic control circuit 1 50.

The other end wall 171 is provided with a hole, coaxial with the cylinder 110, through which passes a piston rod 1 30. Adjacent to end wall 171, to cylindrical wall of cylinder 110 contains two ports 175 and 1 76. Both of these ports enter the bore of the cylinder in section 116 of that bore. Between the points of entry of port 1 75 and 176 is, for constructional reasons, a retained ring 1 77 which passes around the inside of section 11 6 of the bore, such that the external diameter of the ring is the same as of section 11 6, and the internal diameter of the ring is the same and the diameter of section 11 8 of the bore. Both of the ports 175 and 1 76 are connected to the hydraulic control circuit 1 50.

Piston 120 is attached at one end 124 to the piston rod 130. At the other end 125 of the piston has been driven a bore 122. The bore 122 is cylindrical and coaxial with the piston and piston rod. There are six holes 128, from the bore 122 to the outer cylindrical surface of the piston body 129. In a similar manner to holes 28 in the piston of the first embodiment, the holes 128 are equidistant from the end 125 of the piston, and are spaced symmetrically around the axis of the piston. Within each hole 128 is a steel bali 140.

Within the bore 122 is a slug 123, which is cylindrical along the majority of its axis, the diameter of this cylindrical portion 11 9 being only slightly less than the internal diameter of bore 122. Seals 121 are provided to seal the slug 123 and piston 124 against fluid leakage. A section 126 of the slug adjacent end 145 of the slug is also cylindrical, but has a smaller diameter than the portion 11 9 of the slug. Section 126 is coaxial with the rest of the slug, the two cylindrical sections of the slug 123 lying either side of a conical portion 127 such that the diameter of portion 127 increases smoothly along the axis of the slug towards end 142.

Section 126 has a small enough diameter that when positioned opposite holes 128, the balls 140 may rest on the surface of the slug and lie below surface 29 of the cylinder. The slug 123 is slidable along the bore 122, so that the holes 128 may be variously opposite the section 126 or section 11 9.

The end 142 of the slug furthest away from the piston rod 130 is flat. Around the inside of the bore 122, near the end 125 of the piston is a circlip 144 to prevent the slug 1 23 from coming out of the bore.

The hydraulic circuit 1 50 is similar to control circuit 50, and comprises a pump 151; a control valve 152, a vent 1 53 and a hydraulic motor 154 with hydraulic lines 1 55 to 1 60 between components and the cylinder. Control valve 1 52 has three positions 1 65 to 1 67 for controlling the apparatus, which correspond to positions 1 65 to 1 67 respectively of control valve 1 52. Thus when control valve 1 52 is set in position 1 67 the hydraulic pressure from the pump 1 51 is transmitted to hydraulic line 1 57 and thus into cylinder 110 via port 174.This pressure will thus act against piston 20 to force the piston towards end wall 171. The pressure on the end 124 of the piston is atmospheric, as port 1 76 is connected to hydraulic line 1 55 which is connected via valve 152 to the vent 1 53.

Thus when control valve 1 52 is in position 1 67, there is hydraulic pressure on end 142 of the slug which urges slug 123 along the bore 122 towards the piston rod 130. The movement of slug 123 along the bore is impeded by the balls 140 which are restrained from protruding out of the piston 120 by the walls of the cylinder 130 in section 11 8. However, as the piston 120 approaches the end 171 the balls 140 will come opposite section 11 6 and thus will be able to protrude from the side of the piston 120. The pressure on the slug 123 is still urging it towards the piston rod 130 and so the balls 140, which have previously been resting on portion 126 of the slug will now roll up conical portion 127 as the slug 123 starts to move.As the slug 123 continues to move the balls will roll onto portion 119 of the slug. At this point the balls are protruding through the holes 128 and are prevented from receding into the piston again.

Thus because when the balls are protruding the effective diameter of piston 120 is greater than the diameter of section 118 of the cylinder, the piston is now mechanically locked adjacent to end 1 71 of the cylinder against the conical portion 11 7. In this condition the piston body 129 will be lying within the ring 177, a requirement of the release action.

To release the piston from its locked state, the control valve 1 52 is moved to position 165. In this position, hydraulic line 1 58 becomes connected to port 176. Thus the hydraulic pressure from pump 1 51 is now directed to port 176, and the whole of cylinder 110 is vented to the atmosphere.

When the piston is in its locked state, the holes 128 are adjacent to port 176. As hydraulic fluid is applied via port 176, a pressure build-up occurs because its exit from port 1 75 is blocked by-way of the piston body 129 lying within the ring 1 77, so maximum pressure available will be transmitted through the holes 128 and into the closed end of bore 122. The hydraulic pressure will thus act on end 145 of the slug 123, and urge the slug along the bore 122. Since the pressure on end 142 of the slug is substantially atmospheric, the slug 123 will move along the bore 122, away from the piston rod 130, until prevented from further movement by circlip 144.

Thus portion 127 of the slug is once again aligned opposite the holes 128. The balls 140 may thus retract into the holes 128 to lie against portion 127 of the slug, and so may lie flush with the cylindrical surface 129 of the piston, rather than protruding from this surface. As the piston 120 moves, and balls 140 being in contact with section 11 7 which is conical or tapered, the balls 1 40 are caused to be eased deeper into the holes 128, so that they lie against portion 126 of the slug.

As the piston 1 20 continues to move the balls 140 reach section 118 of the bore of the cylinder, by which time they will be flush with the cylindrical surface 129 of the cylinder, allowing the piston 1 20 to pass freely along the length of the cylinder. Also the piston body 129 will be withdrawn from the inner diameter of the ring 177 allowing a free passage of fluid to exit from port 175 via line 1 59 to the hydraulic motor 1 54.

As the pressure to drive the hydraulic motor 1 54 will also be caused to act on the piston causing it to retract so operating a mechanism to move a brush assembly into its work position. A return line 1 60 from the motor connects with the vent 153.

Claims

1. A hydraulic cylinder, having an enlarged diameter portion adjacent to one end, a piston slidable in the cylinder a bore formed in and coaxial with the piston, an actuating piston member slidable in the bore, at least one locking member associated with the piston and a duct means for supplying fluid to the bore, the arrangement being such that: when the piston is nearing the enlarged end of the cylinder, the actuating piston member is forced to move in such a way that this actuating piston member causes the locking member to engage the enlarged diameter portion of the cylinder, thus locking the piston in this end of the cylinder; when fluid pressure is applied via the duct to the actuating piston member, said member is moved by hydraulically applied force in such a way that actuating piston member causes the locking member to disengage the enlarged diameter portion of the cylinder, thus unlocking the piston.

2. A hydraulic cylinder and piston arrangement as claimed in claim 1 in which there is a plurality of locking members.

3. A hydraulic cylinder and piston arrangement as claimed in either of claims 1 or 2, in which the duct means connects the bore with the face of the piston furthest from the piston rod, and in which a force is applied to the end of the actuating piston member furthest from the piston rod, to urge the actuating piston member in the direction of the piston rod, to cause the locking member to engage the enlarged diameter portion of the cylinder if the piston is adjacent to said portion.

4. A hydraulic cylinder and piston arrangement as claimed in claim 3, in which the force applied to the end of the actuating piston member furthest from the piston rod is due to hydraulic pressure within the cylinder acting on said end of the actuating piston member.

5. A hydraulic cylinder and piston arrangement as claimed in claim 3, wherein a pin, which is fixed to the actuating piston member, protrudes along said duct, such that a force applied to the free end of said pin will be transmitted to said end of the actuating piston member.

6. A hydraulic cylinder and piston arrangement as claimed in claim 5 in which the pressure on the pin that causes locking is hydraulic pressure from fluid within the cylinder.

7. A hydraulic cylinder and piston arrangement as claimed in claim 5 in which the pressure on the pin that causes locking is caused by mechanical contact of the free end of the pin with the end of the cylinder as the piston approaches said end of the cylinder.

8. A hydraulic cylinder and piston arrangement as claimed in any of the preceding claims, in which the locking members are balls within generally circular ports, said ports connecting the bore within the piston to the cylindrical surface of the piston.

9. A hydraulic cylinder and piston arrangement as claimed in claim8, in which the actuating piston member has a tapered portion, such that movement of the actuating piston member in the bore will cause the balls to roll along the tapered portion and thus protrude from the piston side.

1 0. A hydraulic cylinder and piston arrangement as claimed in claim 9, in which the actuating piston member has two tapered portions arranged to define a groove around said actuating member, such that movement of the actuating piston member in the bore will cause the balls to roll out of the groove and so protrude from the piston side.

11. A hydraulic cylinder and piston arrangement as hereinbefore described, and as shown in the accompanying drawings.