This invention relates to a control system for a percussion drill.

A percussive drilling circuit normally includes a drilling power pack with hydraulic pumps and a power source which may either be an electric motor or a fuel driven engine, a drilling control panel with separate control valves and control means for controlling drill percussion, drill rotation and drill feed, a drill feed and a percussive hydraulic drill. The control means can be either direct control levers to operate main control valves, additional control valves and levers to pilot control the main control valves, or additional control levers for electrical piloting of the main control valves or additional control levers to operate the main valves through operating cables.

Most commonly the percussion, rotation and feed mechanisms have separate direct operated control valves and valve levers. The hydraulic fluid flow from these valves is directed through a drilling control panel.

As a large amount of hydraulic fluid for the percussion mechanism passes through the percussion control valve, in the control panel, relatively thick hydraulic hoses are required and the drilling circuit becomes complex. A complex circuit on the control panel results in an increased likelihood of oil leakages, increased maintenance, greater expense, difficulty in locating malfunctions in the circuit, and heavier demands for satisfactory operator and maintenance personnel training. A large control panel is difficult to mount ergonomically on a drilling machine without affecting the operator's visibility.

Finnish patents Nos.86008 and 900834 describe different

control systems. In the latter case the drilling feeding speed is monitored and hydraulically linked to drill rotation speed, increasing when drilling speed increases and decreasing when drilling speed drops.

The hydraulic connection optimizes the drill rotation speed with the drilling speed thereby minimizing wear of the drill bit.

In the former case the pressure ratio between drill percussion and drill feed is kept constant with an adjustable piloted displacement pump and a hydraulic circuit. The ratio between percussion power and drill feed force is kept constant. By piloting the pump the oil flow to the drill is increased or decreased in direct response to the pressure in the drill fee control circuit.

The aforementioned problems can be avoided by using a variable displacement pump and by controlling the pressure remotely, for example by means of an electric, hydraulic, pneumatic or mechanical pilot control device. However, with this kind of solution, the advantage of using a simple, cheap, dirt-tolerant, fixed displacement pump like a gear pump is lost, and the circuitry becomes complex, difficult to maintain, expensive and, due to the variable displacement pump, sensitive to dirt.

The invention provides a control system for a percussion drill with a hydraulically actuated drill rotation mechanism and a hydraulically actuated drill feed mechanism which includes control means which in reaction to the hydraulic pressure in the drill feed mechanism or in the drill rotation mechanism or both of these hydraulic pressures, operates to stall a percussion movement of the drill.

In one embodiment the control means operates only in

reaction to the hydraulic pressure in the drill feed mechanism and, upon starting percussive movement of the drill, simultaneously starts rotary movement of the drill.

The drill feed mechanism may be any suitable device and for example may be a drill feed cylinder.

The system may include a pump, which preferably is a fixed displacement pump such as a dirt tolerant gear pump, for supplying hydraulic fluid to a percussion mechanism of the drill, with the control means comprising valve means for directing the supply of hydraulic fluid from the pump to the percussion mechanism to start the percussion when the drill feed mechanism is pressurized.

The valve means is preferably directly connected to the pump means.

The invention is further described by way of example with reference to the accompanying drawing whose single figure is a schematic illustration of a hydraulic control system for a percussion drill, according to one form of the invention.

The accompanying drawing illustrates various modules and components which are identified as follows: a drill percussion mechanism 10, a drill rotation motor 12, a drill feed cylinder 14, a valve 16, a tank 18, a mechanical stop 20, an anti-jamming manifold 22 which includes a directional valve 24 and a pressure reducing valve 26, a drill feed line 28, a module 30 with a collaring flow control valve 32, a feed pressure reducing valve 34, and a pilot operated control valve 35, one-way check valves 36, a feed control valve block 38, a shuttle valve 40, pilot lines 41 and 42, a rotation control valve 44, a percussion control manifold 46 which includes a percussion control

valve 48 and a relief valve 50, and fixed displacement gear pumps 52, 54 and 56 respectively for percussion, rotation and boom movement. The percussion control in manifold 46 is directly connected to the percussion pump 52 separate from the drilling control panel.

The operation of the hydraulic circuit is described hereinafter for single pass drilling with reference to various drilling modes.

Free Circulation

The accompanying diagram illustrates a situation wherein the pumps 52 to 56 are operating but with the control valves 44 and 38 in centre positions. Therefore no drilling takes place.

Hydraulic fluid is delivered by the percussion pump 52 to the pressure inlet in the percussion control manifold 46. The spool of . the percussion control valve 48 is in a position at which hydraulic fluid flow is directed to the oil tank.

The rotation pump 54 delivers hydraulic fluid to the pressure inlet of the rotation control valve 44. The spool of this valve is in a centre position and consequently the valve directs fluid flow to the oil tank.

The boom pump 56 delivers hydraulic fluid to the pressure inlet of the feed control valve block 38. The spools of this valve are also in the centre position and fluid is passing to the oil tank.

Collaring

When the lever of the rotation control valve 44 is actuated the spool of the valve moves to a position at which

hydraulic fluid from the rotation pump 54 is directed to the rotation motor 12.

If the lever of the feed control valve 38 is actuated then fluid from the boom pump 56 is directed through the collaring flow control valve 32, the one-way check valve 36 and the anti-jamming manifold 22 to the drill feed cylinder 14.

Percussion does not start before the drill bit comes into contact with the rock face. When the bit does contact the rock face this causes an increase in pressure in the hydraulic feed circuit which in turn activates the percussion control valve 48 closing it and starting the percussion. The percussion pressure is set to stay at a predetermined constant level with a separate pressure relief 50.

Drilling

It is necessary to release the lever of the feed control valve 38 when percussion of the drill starts. The spool of the valve, which is spring centred, then directs hydraulic fluid from the boom pump 56 back to the oil tank. At this point the percussion pump 52 takes over and supplies hydraulic fluid to the drill feed cylinder 44 through the feed pressure reducing valve 34. The percussion control valve 48 is by now fully closed and percussion runs at full power. The percussion pressure is adjusted with the relief valve 50.

The drilling can be interrupted at any moment by pressurizing the pilot line 41 with the control valve 38. The valve 35 connects the percussion control pilot line 42 to tank and turns the percussion control valve 48 on free flow to tank.

Anti-jamming

If the drill bit meets broken ground or if there is a lack of flushing or if any other unusual situation occurs, which results in a rotation pressure increase, then the connection between the rotation circuit and the anti¬ jamming directional valve 24 causes an immediate reversal of the drill feed cylinder 14. This results in a decrease of the rotation pressure whereupon the directional valve 24 returns to its original position and drilling recommences. The sensitivity of the anti-jamming operation can be adjusted by means of the pressure reducing valve 26.

Return

When the drill feed cylinder 14 has advanced to its maximum extent it comes into contact with the mechanical front end stop 20. This opens the feed supply to the tank and, since the pressure in the feed circuit now drops off, the percussion also stops. The percussion control valve 48 was held in the closed position by the feed pressure and it therefore returns to a position at which the hydraulic fluid delivered by the percussion pump 52 is returned to the tank.

Rotation of the drill however continues. The drill is returned manually with the drill feed cylinder 14 by moving the lever of the feed control valve 38 to a forward position. The boom pump 56 supplies hydraulic fluid for rapid feeding. The anti-jamming feature, described hereinbefore, is operative during return motion and if the drill bit gets stuck during reverse movement of the drill feed cylinder, the direction of movement of the drill feed cylinder is immediately reversed and then returned when the rotation pressure decreases.

Percussion only

If percussion without rotation is required, for example during drill bit loosening, this can be achieved by moving the other lever of the feed control valve 38 forward so that hydraulic fluid from the shuttle valve 40 pressurizes the pilot line 42 and closes the tank connection with the percussion control valve 48 whereupon percussion starts. A light feed force can be applied simultaneously by pulling on the lever of the feed control valve 38.

It is apparent that through the use of the control circuit of the invention percussion does not commence unless the feed pressure activates the percussion control valve to close. Conversely the hydraulic fluid for the percussion is always on free flow when percussion is not required.

While drilling the valve 48, which is a normally open pilot-to-close valve cartridge, is fully closed and the percussion pressure is present to the predetermined maximum level with the valve 50. It follows that the operator can adjust the drilling feed pressure and force with the reducing valve 34 according to rock hardness and drilling penetration speed but can not adjust the percussion pressure on the drill while drilling, without losing the maximum drilling percussion power supplied from the drill.

It also follows that the operator cannot damage the drill by keeping the percussion on without drilling. The main control valve for percussion in the control panel, which is encountered in prior art devices known to the applicant is therefore not needed. The circuit has less hosing, is simpler and is easier to maintain. The training of operating and maintenance personnel is simplified.

The small and simple free flow control valve manifold 46 can be connected preferably directly to the pump or oil filter or the tank and, as has been indicated, the valve 48

is closed only when drilling takes place. The fact that this valve is relatively close to the tank means that fewer hoses are needed and less heat is generated in the system.

The drilling control panel is small in size and simple to operate and the cost of the hydraulic circuit is relatively low due to a reduction in the number of valves and in the hosing. A small size control panel is easy to locate on a drilling unit without affecting the operator's ergonomy and visibility to drill.

The valve 16 is optional and is located close to the drill rotation motor. Its use however allows relatively small hydraulic hoses to be used because it directs return hydraulic fluid flow directly to the tank 18. If the valve 16 is dispensed with then the restriction of the return hose is increased to a point at which undesirable pressure drops occur which, in turn increase fluid restriction and accordingly heat buildup. It also raises the operating pressure level, loading the hydraulic pump. Alternatively the valve 16 could be dispensed with but then bigger size hoses are needed to avoid restriction in the hoses. The circuitry needs more space with big size hoses making it more expensive and difficult to maintain.

The circuit has been described with reference to single pass drilling wherein the mechanical stop 20 detects a limiting position of the drill feed cylinder 14. For long hole drilling where use is made of multiple drill rods the mechanical stop 20 is dispensed with and the return motion of the drill feed cylinder 14 is under the direct control of the operator who determines at which point additional drill rods are added to the drill string.

Also, an embodiment of the invention has been described wherein the pressure in the pilot line 42, reacting to the pressure in the drill feed line 28, is used to control the

valve 48, to start the percussive movement of the drill. The invention is however not limited in this respect for by monitoring the pressure of the hydraulic fluid supplied to the drill rotation motor 12, in a manner analogous to that described, percussive movement of the drill can be started. Thus, depending on the requirement, the percussion movement of the drill can be started by a control device which is dependent on the pressure to the drill feed mechanism, or on the pressure to the drill rotation mechanism, or on both of these pressures.

The control system described hereinbefore makes it possible to use a fixed displacement pump 52 for the percussive movement of the drill, with the attendant advantages which have been described in the preamble to the specification. It is to be noted that the control valve 48 is directly connected to the pump 52 and that this simplifies the circuitry.

Referring to the prior art discussed in the preamble hereto, it is apparent that in the invention the pressure applied to the drill feed mechanism is used to pilot the free flow valve connected to a fixed displacement gear pump and the drill percussion starts with full power. The percussion pressure is adjusted with a separate fixed value pressure relief valve and the percussion only stops or starts by applying pressure for the free flow valve pilot. The pilot activates the free flow valve to close and thus increasing percussion pressure. The free flow connection from the pump to the tank is totally closed.