This invention relates to improvements in hydraulic hammers of the kind used in post drivers and rock breakers.

Background to the invention

Because of variations in the ground and in the posts it is sometimes necessary to reduce the blow energy of the hammer. In accelerated hammers there are 2 sources of downward pressure on the Hammer namely from the hydraulic system and from the gas in the hammer back head.

In the Hydraulic hammer industry there are currently two conceptual ways of changing the blow energy of a particular hammer.

One is the manufacturer incorporates an internal design that allows the hammer to change it's stroke or driving pressure. An alternative and cheaper method is an external compressed nitrogen cylinder, pressure regulator and fitting to adjust the initial back head pressure. This latter approach is good in theory, but difficult in practice due to constraints in available time and knowledge of the operator. Also the components are sensitive to damage, if left in situ between changes in blow energy. It is an object of this invention to ameliorate these problems.

Brief description of the invention

To this end the present invention provides a device for use with a hydraulic hammer of the type that uses a back head gas chamber in which a gas pump and gas container is connected to the hammer back head gas chamber and the hydraulic energy of the hammer hydraulic circuit is used to pump gas from the back head chamber to said gas container to reduce the blow energy of the hammer.

By reducing the pressure in the back head the blow energy can be incrementally reduced. In this invention the hydraulic circuit is tapped to provide energy to pump gas from the hammer gas chamber to a storage chamber to reduce the available hammer force. The transferred gas can be returned to the hammer gas chamber to restore the normal blow force.

The device includes a pump which consists of a piston which moves within a chamber having three sub chambers and one sub chamber is connectable to said back head gas chamber of said hydraulic hammer and also connected to said nitrogen gas container, while the other two sub chambers are connected via a change of direction valve to the hydraulic circuit of said hydraulic hammer.

The device of this invention may be fitted to a post driver from new or with very little fitting work. It may be fitted to any hydraulic post driver of the simple design that is generally used in Australia. It may also be used in the hydraulic rock breaking market.

Detailed description of the invention

A preferred embodiment of the invention will now be described with reference to the drawings in which:

Figure 1 is a schematic layout the device of this invention;

Figures 2 and 3 are a perspective views of the device of this invention;

Figure 4 is a side view of the device shown in figures 2 and 3;

Figure 5 illustrates the piston in the central position of the pump in pumping nitrogen into the storage chamber;

Figure 6 illustrates the piston at its end of travel;

Figure 7 illustrates the piston drawing nitrogen into pump chamber;

Figure 8 illustrates the piston at its opposite end of travel.

The device of this invention consists of a nitrogen storage chamber 12 and a piston 2 moveable within adjacent chambers 21 , 23 and 24 of the pump 20. The piston 2 is driven by the hydraulic pressure from the hammer circuit 27 of the hydraulic hammer in a post driving machine. In each piston cycle, nitrogen is taken from the back head pressure chamber 31 of the hammer 30 via the flexible hose 32 into the pumping chamber 21 and then into the nitrogen storage chamber 12. This sequence depends on the change of direction valve 3 which is preferably an auto recycling hydraulic control valve.

The parameters for the device are set out in table 1. Table 1 , Design parameter specifications

The hydraulic and nitrogen connections are schematically shown in figure 1. The pump sequence is shown in figures 5 to 8.

As shown in figures 5 to 8 and 3 the pump consists of chambers 21 , 23 and 24 and a piston 2 which moves within the pump 20.

In figure 5 the piston is in the central position with high pressure in in chamber 23 driving the piston to the left and pumping nitrogen from chamber 23 through check valve 5 into the nitrogen storage chamber 12.

In figure 6 the piston 2 has reached the end of travel with chambers 21 and 24 empty, due to the high pressure in chamber 23. The change of direction valve 3 now reverses the direction of travel of piston 2 by redirecting the flow of hydraulic fluid. In figure 7 there is now high pressure in chamber 24 and chamber 21 is filling with nitrogen from the back head pressure chamber 31 of the hammer 30 via the flexible hose 32.

In figure 8 the piston is at its opposite end of travel with chamber 23 empty and chamber 21 full of nitrogen and chamber 24 full of hydraulic fluid.

The hydraulic connections are schematically shown in figure 1. The device once connected is controlled by operating the valves on the pressure control block.

To control the pressure in the hammer, the device is operated for a number of cycles until the pressure is reduced by an appropriate value. An example is given in table 2. Table 2, Iterative pressure change calculation of P3 (in chamber 12) over pump cycles. P1(in chamber 31) initiated at 18bar of 1200cc Hammer

The calculations for Table 2 show the rate at which P2 was determined by the following formula.

P ² iniiat = P ¹ Viniiat/Vfinat Where Viniiat = VI and Vfinat = V1 + V ² max

Additionally, P3 rises according to the following formula.

P ³ flnatV ³ + P ² finatV ² min = P ³ iniiatV ³ + P ² iniiatV ² max

Where V2 min is when the piston is at the end of its stroke and for simplicity we let this be zero. The distance from end of stroke was back calculated using the

previous iteration PI value.

P2i = P ^] iJ

The device may be made in accordance with good engineering practice.

Due to the Nitrogen gas being routed through various manifolds and hydraulic oil being used for pumping the O-Ring seals must have good gas impermeability and also good resistance to hydraulic oils.

The piston seals are required to withstand both the high pressures from the hydraulic oil as well as the changing pressures of the pumped nitrogen gas. Due to the reciprocating action of the piston an O-Ring is not preferred because of potential gas or oil leakage upon retraction. Due to the requirement to keep both the working fluids (nitrogen and hydraulic fluids) separate it is preferred to utilize two single acting seals working back to back.

Utilizing two back to back seals provides the required sealing conditions while also making for a larger separation between the two fluids, and therefore reducing the potential for cross contamination. The increased separation also provides room for a center mounted piston bearing which allows for less metal to metal contact, and less reciprocating friction.

The connecting rod is preferably suitable for the conditions set by the hydraulic oil and its operating pressure and temperature. The only stringent requirement is resistance to hydraulic fluids.

The operation of the pump requires the use of one way check valves to ensure that gas reversion does not occur through the various connections. Along with the check valves, there is a need to control the rate of flow into the Hammer gas volume and to either enable or disable the flow based on usage type.

For the operation of the pump a 3way hydraulic valve is required so as to provide a forward, neutral and reverse action for the hydraulic piston. Preferably this valve is an auto recycling hydraulic control valve.

The operational positions of the pump are shown in figures 2 and 3 and figure 4 illustrates schematically the hydraulic connections while figure 5 indicates the main connection points. The advantages of this invention include:

1. able to be retrofitted to an existing hammer

2. Simple to use and relatively quick to raise or lower the blow energy.

3. Small enough package size to fit on a post driver.

4. Uses the initial Gas pressure in the hammer back head as the means of varying the blow energy.

5. Uses the existing hydraulic oil supply on the machine as the energy source for changing the back head gas pressure.

6. Low cost compared with other in situ solutions.

From the above it can be seen that this invention provides a unique and inexpensive means to reduce hammer force in post drivers and rock-breakers. Those skilled in the art will also realise that this invention can be implemented in embodiments other than those described without departing from the core teachings of this invention. For example the gas pump may be any suitable pump including diaphragm pumps.