Device for a hydraulically driven percussion hammer

Device for a hydraulically driven percussion hammer for activating a tool, comprising a differential piston with corresponding cylinder, where the piston's largest surface is closest to the percussion tool, and where the smallest working surface is in direct hydraulic connection with an air tank. The largest working surface is above a multiple valve in connection with a hydraulic pressure medium. The valve is adjustable from an admission position with closed return duct to a position where the admission is blocked and the return duct is open. The piston chamber above the piston's small working surface has a feed duct with back pressure valve for a hydraulic pressure medium.

The present invention relates to a device for a hydraulically driven 
percussion hammer for activating a tool, especially intended as a drilling 
hammer. Most percussion hammers are pneumatic, i.e. they are driven by 
compressed air. This operational form has some obvious disadvantages, so 
that there has been considerable interest in other operational forms e.g. 
hydraulic operation. The disadvantages in pneumatic percussion tools 
consist in their requiring large quantities of air to get sufficient 
energy. This again requires large pipes. Another disadvantage is that the 
air-pipes easily freeze and both the compresser and the percussion tools 
are very noisy. The noise from percussion tools comes partly from the used 
air which is sudden expansion is emitted from the tool's exhaust port. 
A number of different types of hydraulically driven percussion hammers have 
been proposed, and some have also been used in practice. The great 
disadvantage common to the previously known percussion hammers of this 
kind is that great amounts of compressed liquid must be used, 
necessitating large pumps and sizable pipes, in order to obtain sufficient 
effect. 
Hydraulic drilling hammers are also known which comprise a differential 
piston where the pressure medium is admitted to the small piston by 
percussion. Less pressure medium is needed with these percussion hammers, 
but the blow is ineffective for there is too little pressure as the 
pressure sinks rapidly with the rapid expansion when the striking piston 
is displaced in the direction of the stroke. 
Devices are known in addition which are equipped with an accumulator or air 
tank which is loaded by a pressure medium to high pressure and which 
provides for admission by impact. The machines known of until now are 
however, very complicated and expensive, and large admission surfaces on 
the percussion piston are used, so that the impact is ineffective. 
The purpose of the present invention is to eliminate the disadvantages 
mentioned above and to provide a hydraulically driven hammer for 
activating tools, e.g. a drill, which comprises a differential piston with 
corresponding cylinder, where the largest operational surface of the 
piston lies nearest the percussion tool and where the least operational 
surface is in direct hydraulic connection with an air tank, and the 
characteristic of the invention is that the largest working surface over a 
multiple valve is in contact with a hydraulic pressure medium, which valve 
is adjustable from an admission position with blocked return duct to a 
position where the admission is blocked and the return is open, and that 
the piston space over the piston's small working surface has a supply duct 
with back pressure valve for hydraulic pressure medium . 
The hammer according to the invention is simple in its construction and 
applies very great force in the stroke movement. 
In a preferred embodiment, the air tank consists of a cylinder with a 
membrane or a loose piston. The air tank can in a manner known per se have 
an over pressure at maximum expansion.

The device consists of a differential piston with 3 unequal diameters. 
These are marked 1-2 and 3, and can have a forward and backward movement 
in the corresponding cylinders 4-5 and 6. 
The left side will hereafter be called the under side and the right, the 
upper side. Above the piston part which is marked 3 is a gas-filled or 
spring-loaded accumulator of a known type 7, here depicted with a piston 8 
to separate gas and oil. 
A duct for compressed oil 9 with a springloaded back pressure valve 10 
opens out into the chamber 11. This room is at the same time a working 
cylinder for that part of the striking piston which is marked 3. 
The compressed oil goes further through the pipe 12 to a valve 13 which can 
be a rotating valve, kick valve or slide valve of a known type. It can be 
controlled by a motorized knob or crank, or be rotating. Its purpose is to 
block the return duct 15 and to lead the compressed oil as well to the 
under side of the piston part 2 through the duct 14, in connection with 
the return duct 15. (Shown with dotted line). 
A duct 16 with a spring-loaded back pressure valve 17 can emit any possible 
oil leakage which passes by the piston parts 2 and 3. This oil goes to the 
return pipe. 
The lining for the differential piston consists of pipe-shaped cylinders, 
4-5 and 6. 
The piston must be fairly long, and both this and the cylinders must be 
exactly fitted to each other in order to obtain a sealing with at the same 
time a sliding fit. 
It is well known that it is very difficult to join such cylinder parts 
together without crookedness occuring with accompanying overheating and 
seizing as a result. 
One of the reasons for this is that if these parts are screwed together 
with collecting bolts, they must be tightened with exactly the same 
tension. If they are tightened unevenly, the elasticity in the material 
will cause lob-sidedness and thereby wedging. 
If the material is exposed to jolting or blows, tensions may occur which 
can cause crookedness. 
The cylinder head 19 does not lie against the lining 6. This lining is 
provided with a tightening ring 22. The bore in the sheet metal 18 can 
have a slightly larger diameter than the outer diameter on the linings. 
The uppermost lining 6 can have a larger outer diameter than the others, 
or have a larger diameter uppermost at the tightening ring. 
It is assumed that the lining is exactly right-angled, lathed, in relation 
to inner bores in the latter, which does not constitute any technical 
difficulties. 
The packing between the linings and between the linings and the sheet 
metal, moreover, can be packing material, gaskets or O-rings as shown in 
the drawing. 
The effect is as follows: The compressed oil comes in through the pipe 9 
through the valve 10 and fills the cylinder 11, and as there is an opening 
between the lining 6 and the cylinder head 19, the oil will bring pressure 
to bear on the surface of the lining 6 which is not drilled and press all 
the linings together with a tight connection. 
And because there is clearance between the inner diameter on the bore in 
the block and the outer diameter on the linings, these will find their lie 
and adjust to the piston even if there should be deviations in direction 
on the bore in the block. 
The effect on the striking mechanism is as follows: 
A prototype of the device according to the invention works in the following 
way: The piston part 3 has an activating surface of 2 cm.sup.2 and the 
ring-shaped piston surface 2 is 4 cm.sup.2. The lower end of the piston 
part 1 lies against a tool (not shown), e.g. a drilling knob, which 
absorbs the striking energy. It is assumed that the valve 13 is in such a 
position that the compressed oil is blocked to the duct 14, while the 
latter is in open connection with the return pipe 15. (Shown on the 
drawing with a dotted line.) It is similarly assumed that the air tank 7 
is filled with a gas pressure of 50 ato and the piston 8 lies against the 
bottom of the air tank and seals against leakage. The chamber above the 
piston 8 has a volume of 40 cm.sup.3 and the working pressure on the oil 
is 100 ato. 
The compressed oil streams in through the valve 10 and fills up the chamber 
11. The piston 8 is then driven upwards to the point where the gas gets a 
pressure of 100 ato. The volume in the chamber above the piston 8 is then 
20 cm.sup.3. Any possible leakage oil will be filled again through valve 
10. 
The oil exerts now a standing axial force of almost 200 kp. on the end 
surface of the piston 3. The valve 13 is turned now in such a way that the 
return duct is blocked and the compressed oil comes into the duct 14 and 
under the ring piston 2. As the working surface on this piston is 4 
cm.sup.2, the piston will be exposed to an axial force of 400 kp. and will 
move upwards. The back pressure valve 10 is closed and the oil above the 
piston part 3 is pressed into the accumulator under the piston 8. When the 
piston has moved 5 cm upwards, the piston part 3 has displaced 10 cm.sup.3 
oil. The piston has thereby been displaced upward so that the volume in 
the gas become 10 cm.sup.3 and the pressure 200 ato. A balance is thereby 
achieved between the axial pressure under the piston part 2 and the 
pressure over the piston part 3 and the piston stops. Now the valve 13 
again shuts for the working pressure and sets duct 14 in connection with 
the return pipe 15. There is now no noticeable resistance under the piston 
part 2 and the piston goes downward and executes the percussion, after 
which the process is repeated. The dimensions given are only included as 
an example, and can be varied within the framework of the invention. 
The energy of the stroke can be varied with other dimensions, other 
pressure conditions, and the length of the stroke can be varied with e.g. 
greater or lesser volume in the air tank 7. The liquid pressure which is 
to be constant in the chamber 11 can also come from a separate pressure 
source. Duct 9 will then not be connected with duct 12 but with another 
possible pressure source. By varying this pressure the length of stroke 
can be varied as desired without changing the size of the air tank 7 or 
changing the gas pressure in the latter. There is a constant pressure in 
the duct 12. 
By means of the device according to the invention, a hydraulically driven 
percussion hammer is obtained for activating a tool, which operates with 
very small amounts of oil and where the stroke energy within wide limits 
can be adjusted according to need. The hammer can be made small and light 
and will be very silent in operation.