GB2221498A

GB2221498A - Liquid pressure impulse generator

Info

Publication number: GB2221498A
Application number: GB8818321A
Authority: GB
Inventors: Paul Snowden
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-08-02
Filing date: 1988-08-02
Publication date: 1990-02-07
Anticipated expiration: 2008-08-02
Also published as: GB8818321D0; GB2221498B

Abstract

A liquid pressure impulse generator includes a generator cylinder sub-assembly 1 containing two pistons 2 and 3 interconnected by a rod for reciprocation in respective cylinders 5 and 6 to impart impulses longitudinally of the cylinders 5 and 6 to an hydraulic fluid having a viscosity less than 50 centistokes in an hydraulic circuit which includes the cylinders 5 and 6 and a capacitor 9. Lubricating fluid is fed to the inner cylindrical surface of each cylinder 5, 6 for lubricating the movement of the piston 2, 3 during a start-up period when the piston is being reciprocated from rest to a desired speed of reciprocation. Each cylinder 5, 6 is in the form of a sleeve mounted in a block, the latter having an aperture for feeding lubricating fluid to a circumferential recess in the outer surface of the sleeve. Lubricating fluid flows from the recess through radial holes to the inner cylindrical surface. <IMAGE>

Description

LIQUID PRESSURE IMPULSE GENERATOR The present invention relates to liquid pressure impulse generators more particularly, but not exclusively, for use with hydraulically operated impact or vibratory devices otherwise referred to as AC hydraulic hammers. An example of an AC hydraulic hammer is described in my British Patent No. 1,340,521.

In order to operate such a device, a liquid pressure impulse generator must be started from rest and brought to a desired speed of longitudinal oscillation at which the impact or vibratory device is to be operated. During this start-up period the piston of a piston and cylinder assembly is reciprocated without any hydraulic fluid in the piston and cylinder assembly. A difficulty has been experienced in providing for adequate lubrication of the piston during this initial start-up period when the hydraulic fluid used is a low viscosity fluid, ie. the fluid has a viscosity less than 50 centistokes as disclosed in my co-pending Patent Application Neo.8817538 , because the fluid drains out of the piston and cylinder assembly when this is at rest.The preferred low viscosity fluid described in the said Patent Application comprises 95% water and 5% emulsifying oil and has a viscosity of 20 centistokes.

According to the present invention there is provided a liquid pressure impulse generator including a piston and cylinder assembly of which the piston is reciprocable in the cylinder to impart impulses longitudinally of the cylinder to an hydraulic fluid having a viscosity less than 50 centistokes in an hydraulic circuit which includes the cylinder and a capacitor, the outer cylindrical surface of the cylinder having a circumferential recess therein and there being a plurality of radial holes connecting the circumferential recess with the inner circumferential surface of the cylinder, and means being provided for feeding lubricating fluid to the circumferential recess and thence to the inner cylindrical surface of the cylinder for lubricating the movement of the piston in the cylinder during a start-up period when the piston is being reciprocated from rest to a desired speed of reciprocation.

Preferably the circumferential recess is located substantially equi-distant from the opposite ends of the cylinder.

The lubricating feed used in accordance with this invention is preferably the hydraulic fluid used in the hydraulic circuit.

The present invention will be further understood from the following detailed description of a preferred embodiment thereof which is made, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of the hydraulic circuit of a liquid pressure impulse generator, Figure 2 is a cross-sectional side view of part of the generator cylinder sub-assembly of the liquid pressure impulse generator of Figure 1, and Figure 3 is a cross-sectional view of the piston of the generator cylinder sub-assembly of Figure 2.

In Figure 1 of the accompanying drawings there is shown diagrammatically the hydraulic circuit of a liquid pressure impulse generator. A generator cylinder sub-assembly 1 contains two pistons 2 and 3 inter-connected by a rod 4 for reciprocation in respective cylinders 5 and 6. The pistons 2 and 3 are moved in the cylinders 5 and 6 by means of crankshafts connected to a driven motor (not shown). Also not shown is a flywheel which keeps the reciprocation of the pistons going at the desired frequency when the generator has built up to this frequency.

The ends of the cylinders 5 and 6 are connected through conduits 7 and 8 to a capacitor 9 which, in operation of the generator, contains a large volume of the hydraulic fluid. One end of the capacitor 9 is connected directly to a valve 10 and the other end of the capacitor 9 is connected through a 3-way junction 11 to a further valve 12. The valves 10 and 12 control the flow of hydraulic fluid to respective conduits 13 each leading to an AC hydraulic hammer, so that two hammers may be driven from the one generator.

A pump 14 is provided for feeding low viscosity fluid from a reservoir 17 through either or both of an on/off valve 15 and a restrictor valve 16.

When the liquid pressure impulse generator of Figure 1 is started from rest, the valve 15 is open so that the low viscosity fluid is passed as a lubricating fluid to each of the cylinders 5 and 6 for lubricating the movement of pistons 2 and 3 in a manner the details of which will be described with reference to Figure 2. As the generator is working up to speed there is no hydraulic fluid in the circuit but, once the desired speed of reciprocation of the pistons 2 and 3 is reached, the restrictor valve 16 is opened so that the pump 14 may pump the low viscosity fluid, which is preferably a water-based fluid, from a reservoir 17 into the circuit comprising the capacitor 9, conduits 7 and 8 and cylinders 5 and 6.Once the hydraulic fluid is being reciprocated in the circuit, and particularly in capacitor 9 which contains a relatively large mass of the hydraulic fluid, valve 15 is closed. Either or both of the valves 10 or 12 can then be opened so that the liquid pressure impulses may be fed through one or both conduits 13 to an AC hydraulic hammer.

In Figure 2 of the accompanying drawings there is shown a cross-sectional side view of that part of the generator cylinder sub-assembly which includes piston 2 shown in cross-section in Figure 3) and cylinder 5. Cylinder 5 is mounted in a block 18 and has an outer cylindrical surface 19 and an inner cylindrical surface 20. The block 18 includes a port 21 connecting the interior of the block 18 and the cylinder 5 to the conduit 7.

When the piston 2 is reciprocated this moves within the inner cylindrical surface 20 of the cylinder 5.

When the generator is started up from rest, the piston 2 is moved longitudinally within the cylinder 5. Although some lubricating oil can be introduced through port 21 onto the piston 2, it is very difficult to lubricate the piston 2 adequately and therefore, according to the present invention, a circumferential recess 22 is provided in the outer cylindrical surface 19 of the cylinder 5 near to the middle of cylinder 5. The circumferential recess 22 is fed with lubricating oil from the pump 14 through a feed aperture 23 drilled in the block 18.

The circumferential recess 22 in the outer cylindrical surface 19 of the cylinder 5 is connected through a plurality of holes 23 drilled radially through the cylinder 5 to connect the circumferential recess 22 to the inner cylindrical surface 20.

By this means lubricating oil is fed to a central part of the piston 2 to lubricate the piston during reciprocation before the hydraulic fluid is introduced, which happens when the piston is operating at the desired speed of reciprocation for driving the AC hydraulic hammer.

Although in the preferred embodiment herein described the low viscosity hydraulic fluid is used as the lubricating fluid, the lubricating fluid could be a fluid compatible with the low viscosity hydraulic fluid, for example the emulsifying oil component of the low viscosity fluid.

Claims

CLAIMS:

1. A liquid pressure impulse generator including a piston and cylinder assembly of which the piston is reciprocable in the cylinder to impart impulses 5longitudinally of the cylinder to an hydraulic fluid having a viscosity less than 50 centistokes in an hydraulic circuit which includes the cylinder and a capacitor, the outer cylindrical surface of the cylinder having a circumferential recess therein and 10 there being a plurality of radial holes connecting the circumferential recess with the inner circumferential surface of the cylinder, and means being provided for feeding lubricating fluid to the circumferential recess and thence to the inner 15 cylindrical surface of the cylinder for lubricating the movement of the piston in the cylinder during a start-up period when the piston is being reciprocated from rest to a desired speed of reciprocation.

2. A liquid pressure impulse generator according 20to Claim 1 wherein the recess is located at a position substantially equi-distant from the opposite ends of the cylinder.

3. A liquid pressure impulse generator according to Claim 1 or Claim 2 wherein the lubricating fluid is the hydraulic fluid used in the hydraulic circuit.

4. A liquid pressure impulse generator substantially as herein described with reference to the accompanying drawings.