ZA200104813B - Hydraulic actuator. - Google Patents

Description

HYDRAULIC ACTUATOR

BACKGROUND TO THE INVENTION

THIS invention relates to hydraulically powered mechanisms.

The specifications of South African patents 92/4302 (Trade Firm 57 (Pty)

Limited) and 96/7417 (White Manufacturing (Pty) Limited), the contents of both of which are incorporated herein by reference, describe hydraulically powered rotary indexing mechanisms for rotationally indexing the drill steel of a water-powered rockdrill. In each case differential hydraulic forces acting on opposed piston assemblies are used to achieve rotary oscillation of a rotor which transmits indexed rotary motion to the drill steel via a one-way clutch and chuck in which the drill steel is engaged.

The piston assembly in each case includes a strut or plunger which has a spherically shaped end seating in a complemental socket in a radially projecting lug or ear on the rotor. A problem inherent in each of these known mechanisms is the fact that the spherical interface between the plunger or strut and the rotor socket is an area of high wear.

CONFIRMATION COPY

SUMMARY OF THE INVENTION :

According to one aspect of the invention there is provided an hydraulically powered mechanism comprising a piston assembly arranged to be driven by hydraulic fluid acting on it in a working zone, an item of equipment which is to be driven by the piston assembly, the piston assembly presenting a face which acts at an interface against a complemental face on the item of equipment. and a fluid supply passage for supplying hydraulic fluid from the working zone to the interface.

The piston assembly may include a piston and a strut which acts between the piston and the item of equipment with a portion of the passage extending through the strut to the interface. The interface may be a spherically curved interface between a spherically curved end of the strut and a spherically curved socket in the item of equipment, and the spherically curved end of the strut can be formed with a flat. The piston itself may be cup-shaped to receive an end of the strut remote from the interface, a portion of the passage extending through the base of the piston, from the working zone, to communicate with that portion of the passage extending through the strut.

There may be piston assemblies acting at spaced apart interfaces on the item of equipment and a port extending through the item of equipment to provide hydraulic communication between the interfaces. This would typically be the case where the mechanism forms part of a rotary indexing mechanism of an hydraulically powered rockdrill which serves to rotate a drill steel with indexed rotation. In this case, the item of equipment will be a rotor with the complemental face provided by a radial lug of the rotor.

In an hydraulically powered rockdrill, another aspect of the invention provides a rotary indexing mechanism for rotationally indexing a drill steel attached to the rockdrill. the mechanism comprising: - a rotor, - opposed piston assemblies arranged to be driven by hydraulic fluid acting on them, the piston assemblies presenting faces which act at respective interfaces against complemental faces on the rotor thereby to drive the rotor in rotary oscillation, means to convert rotary oscillation of the rotor into indexed rotation = of the drill steel, and one or more fluid supply passages for supplying hydraulic fluid to the interfaces.

E Typically in this application the piston assemblies are arranged to be driven by hydraulic fluid acting on them in respective working zones, the mechanism comprising one or more fluid supply passages for supplying hydraulic fluid to the interfaces from at least one of the working zones.

Typically also, each interface is a spherically curved interface between a spherically curved end of a strut and a spherically curved socket in the rotor lug. The spherically curved end of each strut may be formed with a flat and there may be a port extending through the lug to provide hydraulic communication between the interfaces, the flats serving to ensure that such communication is maintained even if the struts rotate somewhat relative to the lug.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a cross-sectional view of a mechanism according to the invention; and

Figure 2 shows a detailed view of the spherical interfaces.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows a rotary indexing mechanism 10 of the kind described in the specification of South African patent 96/7417. The rotary indexing function of the illustrated mechanism 10 is exactly the same as described in this patent specification and is accordingly not repeated here in detail.

The piston assemblies of the mechanism 10 are indicated by the numerals 12 and 14 respectively. The piston assembly 12, which can be referred to as the index piston assembly, includes a hollow, cup-shaped piston 16 of relatively large cross-sectional area in a cylinder 18 supplied with fluctuating hydraulic pressure through a port 20 and a strut 22 having front and rear spherical ends 24 and 26 respectively. The rear spherical end 26 seats complementally in the piston 16 while the front spherical end 24 seats in a complementally spherical socket 28 in a radial lug 30 on a rotor 32 which, via a non- illustrated clutch, acts on a drill steel chuck 34. The piston assembly 14, which can be referred to as the reset piston assembly, is similarly configured with a piston 38 of relatively small cross sectional area and strut 40 with front and rear spherical ends 42 and 44. The front spherical end 42 seats complementally in a spherical socket 46 in the opposite side of the lug 30.

Referring to Figure 2, the spherical interfaces between the front spherical ends 24 and 42 and the associated sockets 28 and 46 arc designated with the numerals 48 and 50 respectively.

A feature of the mechanism 10 which is not described in the specification of patent 96/7417, and which is the subject matter of the present invention, is a passage 52 which extends through the piston assembly 12 to place the port 20 in hydraulic communication with the spherical interface 48. It will be noted that the passage extends through ports 53 in the base of the piston 16 and that the remainder of the passage extends axially through the strut 22 to the front spherical face at the end 24.

In operation of the mechanism 10 pressurised hydraulic fluid supplied to the cylinder 18 through the port 20 can flow through the passage 52 to the interface 48. At the interface, the hydraulic fluid, i.e. water in the case of a ) water-powered rockdrill, provides a wear-reducing wetting and lubricating action between the mating spherical surfaces due to weeping and slight leakage as the mechanism oscillates.

Referring again to Figure 2, it will be seen that the spherical surface at the front end 24 of the strut 22 is formed with a flat 54. The area of the flat is selected to ensure that as the front end 24 rotates slightly relative to the socket 28 during reciprocation of the piston 16 and strut 22, there is always communication between the passage 52 and the interface 48. Although not visible in Figure 1 a similar flat is provided on the spherical surface at the rear end 26 of the strut 22 to ensure that there is always hydraulic communication between the respective portions of the passage 52 which extend through the strut 22 and the piston 16.

A passage corresponding to the passage 52 could be provided in the piston assembly 14 in order to supply pressurised hydraulic fluid to the spherical interface 50. This would require fluid communication to be provided between the supply port 58 and the interior of the cylinder behind the piston 38.

In view of this and furthermore in view of the difficulty and cost of forming a small diameter bore longitudinally in the strut, it is preferrcd merely to provide a port 56 which extends through the lug 30 to place the interfaces 48 and 50 in hydraulic communication with one another and hence to provide the desired wetting and lubricating action at the interface 50.

From Figure 2 it will be seen that the spherical surface at the front end 42 of the strut 40 has a flat 60 similar to, and for the same purpose as, the flat 54.

A similar flat is provided at the rear end of the strut 40 as well, for the purpose described above.

In practice, provided that the areas of the various flats is smaller than the working areas of the associated pistons, the pressurised hydraulic fluid will not be able to urge the pistons, struts and sockets apart from one another.

It will be understood that similar provision for wetting and lubrication of the spherical interfaces could also be made in the case of a rotary indexing mechanism of the kind described in the specification of South African patent 93/4302. In fact, in this case, the formation of the interface supply 52 would he even simpler in that, in the absence of the cup-shaped pistons, there would be a need for a single bore only through the plunger.

© WO 0039468 7 PCT/IB99/02005

The invention envisages that the supply of pressurised hydraulic fluid to the interfaces 48 and 50 could also provide a means for hydraulically powering a clutch for the rotary indexing mechanism. There could, for instance, be further porting in the rotor 32 to lead hydraulic fluid from the interfaces 48 and 50 to a suitable hydraulic clutch (not illustrated) to ensure that rotary motion is transmitted from the oscillating rotor to the drill steel chuck in one direction only.

In the case of the illustrated embodiment, it will be understood that the supply of hydraulic fluid to the interface between the rear ends of the struts and the piston sockets will also serve a wetting, lubricating and hence wear-reducing function.

It will also be understood that as a result of the presence of the flats 54, 60 in the relevant faces. those faces are not perfectly spherical. The term “spherical” is nevertheless used herein for convenience.

Although the invention has been described with specific reference to the rotary indexing mechanism of a rockdrill it will be understood that the principles involved are equaily applicable to other hydraulically powered mechanisms in which hydraulic lubrication is desirable at working interfaces where piston assemblies act against items of equipment which are to be driven by the piston asemblies.

Claims (11)

1. CLAIMS l. An hydraulically powered mechanism comprising a piston assembly arranged to be driven by hydraulic fluid acting on it in a working zone, an item of equipment which is to be driven by the piston assembly, the piston assembly presenting a face which acts at an interface against a complemental face on the item of equipment, and a fluid supply passage for supplying hydraulic tluid from the working zone to the interface.
2. - 2. A mechanism according to claim 1 wherein the piston assembly includes a piston and a strut which acts between the piston and the item of equipment with a portion of the passage extending through the strut to the interface.
3. 3. A mechanism according to claim 2 wherein the interface is a spherically curved interface between a spherically curved end of the strut and a spherically curved socket in the item of equipment.
4. 4. A mechanism according to claim 3 wherein the spherically curved end of the strut is formed with a flat.
5. 7 WO0039468 9 PCT/IB99/02005 A mechanism according to any one of claims 2 to 4 wherein the piston is cup-shaped to receive an end of the strut remote from the interface and a portion of the passage extends through the base of the piston, from the working zone, to communicate with that portion of the passage extending through the strut.
6. 6. A mechanism according to any one of the preceding claims comprising piston assemblies acting at spaced apart interfaces on the item of equipment and a port extending through the item of equipment to provide hydraulic communication between the interfaces.
7. 7. A mechanism according to any one of the preceding claims wherein the mechanism forms part of a rotary indexing mechanism of an hydraulically powered rockdrill which serves to rotate a drill steel with indexed rotation.
8. 8. A mechanism according to claim 7 wherein the item of equipment is a rotor and the complemental face is provided by a radial lug of the rotor.
9. 9. In an hydraulically powered rockdrill, a rotary indexing mechanism for rotationally indexing a drill steel attached to the rockdrill, the mechanism comprising:

   - a rotor, - opposed piston assemblies arranged to be driven by hydraulic fluid acting on them. the piston assemblies presenting faces which act at respective interfaces against complemental faces on the rotor thereby to drive the rotor in rotary oscillation, - means to convert rotary oscillation of the rotor into indexed rotation of the drill steel, and - one or more fluid supply passages for supplying hydraulic fluid to the interfaces.
10. 10. A rotary indexing mechanism according to claim 9 wherein the piston assemblies are arranged to be driven by hydraulic fluid acting on them in respective working zones, the mechanism comprising one or more fluid supply passages for supplying hydraulic fluid to the interfaces from at least one of the working zones.
11. 11. A rotary indexing mechanism according to claim 10 wherein each piston assembly includes a piston and a strut which acts between the piston and a lug on the rotor.