Mole hammer-cycle control

Claim 2

In a Mole comprising an internal front anvil, a hammer having front and rear ends, pressurized fluid drive means having a power stroke mode and a retract stroke mode and including a fluid switch alternately applying said fluid to said hammer rear and front ends to respectively affect said two modes, and wherein said hammer travels between said front anvil and a retracted position defining therebetween an optimum hammer stroke length, the improvement in controlling the operation of said fluid switch comprising: means for continuously deriving a switching parameter G v2/p where v is the instantaneous velocity of said hammer and p is the instantaneous pressure of said fluid, and means responsive to sensing when said parameter G reaches a predetermined value, said fluid switch, said predetermined value being selected to assure said optimum hammer stroke length.

Claim 3

The apparatus of claim 1, further comprising a rear anvil rearwardly adjacent to said retracted position, and wherein said fluid drive means further comprises means for effecting hammer impact on said rear anvil only, by the same said controlled operation of said fluid switch.

Claim 4

A Mole system comprising: an elongated body, a front anvil linked to said body, a hammer having front and rear hydraulic drive ends, means for mounting said hammer within said body for linear movement between said front anvil and a retracted position defining therebetween a maximum hammer stroke length physically permissible, pressurized hydraulic drive means having a power stroke state and a retract stroke state and comprising supply and return hydraulic lines, means, operative only during said retract stroke and including an orifice connected in series with said hydraulic drive means, for generating a pressure difference PL - PH, where PL is the difference between said supply and said return line pressures, and PH is the difference in pressure between said hammer front and rear ends, means including power spool means for alternately supplying hydraulic fluid from said supply line to said hammer rear and front ends to respectively affect said two modes, and pilot valve means having first and second states, and connected to said power spool means and having a first pair of opposed pressure regions each of area A2 connected to said hammer front and rear ends, a second pair of opposed pressure regions each of area A1 connected to said supply and to said return lines, where the ratio A1/A2 is a positive fraction, said pilot valve means further comprising means operating when (A1/A2) PL - PH > or = 0, to effect a switch in said states, thereby to switch said drive means, from said power stroke mode to said retract stroke mode, and third means responsive to a predetermined value of difference between said first sensed pressure and said second sensed pressure the latter scaled by the factor A1/A2 sensed by said first and second sensing means for operating said pilot spool means.

Claim 5

A Mole system comprising: an elongated body, a front anvil linked to said body, a hammer having front and rear hydraulic drive ends, means for mounting said hammer within said body for linear movement between said front anvil and a retracted position defining therebetween a maximum hammer stroke length physically permissible, pressurized hydraulic drive means having a power stroke state and a retract stroke state and comprising supply and return hydraulic lines, means, operative only during said retract stroke and including an orifice connected in series with said hydraulic drive means, for generating a pressure difference PL - PH, where PL is the difference between said supply and said return line pressures, and PH is the difference in pressure between said hammer front and rear ends, means including power spool means for alternately supplying hydraulic fluid from said supply line to said hammer rear and front ends to respectively affect said two modes, and pilot valve means having first and second states, and connected to said power spool means and having a first pair of opposed pressure regions each of area A2 connected to said hammer front and rear ends, a second pair of opposed pressure regions each of area A1 connected to said supply and to said return lines, where the ratio A1/A2 is a positive fraction, said pilot valve means further comprising means operating when (A1/A2) PL - PH > or = 0, to effect a switch in said states, thereby to switch said drive means, from said power stroke mode to said retract stroke mode, and third means responsive to a predetermined value of difference between said first sensed pressure and said second sensed pressure the latter scaled by the factor A1/A2 sensed by said first and second sensing means for operating said pilot spool means.

Claim 6

Apparatus pursuant to claim 3, further comprising means including movement of said power spool means for placing said orifice means in series with said supply line during said retract stroke, said orifice means being by-passed by said supply line flow during said power stroke, means connecting said orifice means during said retract stroke to said hammer front end, said orifice developing a pressure difference thereacross that is proportional to the velocity squared of said hammer, the proportionally Constant being selected to assure said maximum hammer stroke length physically permissible and wherein the ratio A1/A2 is in a range between 0.4 and 0.7.

Claim 7

Apparatus pursuant to claim 3, further comprising a rear anvil rearwardly adjacent to said retracted position, and wherein said fluid drive means further comprises means for effecting hammer impact on said rear anvil only, by the same said controlled operation of said fluid switch.