Invention relates to a hammering apparatus functioning with a pressurized medium, such as with a pressure fluid of a hydraulic system (pressure medium) which hammering apparatus comprises an elongated body which can be attached to a power tool, a movable impact mass adjusted to be resting on the body for which impact mass a linear control part is adjusted to the mentioned body and an arrangement for lifting the movable mass up for the impact comprising the first cylinder and a piston which can be moved in it with the help of a pressure fluid and comprising the piston rod in which case in the arrangement the mentioned piston rod is attached to the mentioned mass and comprises a valve arrangement with the help of which the pressure of the hydraulic fluid can be directed to the first cylinder to the other side of the piston for the uplifting of the mass and the mentioned pressure can be reduced suddenly when the mass is being directed to impact.

A hammering apparatus performing impacts downwards with the help of a mass which can be lifted up is previously known for example from the publication WO 03097945 in which several hydraulic cylinders are located outside the mass with which cylinders the mass is both lifted up and with the help of them also pressure is allocated to the gas spaces located at the other side of the pistons located in the cylinders with which pressure the mass is accelerated during the impact. For the duration of the impact the hydraulic pressure is removed from the cylinders. This solution has the disadvantage that during the impact the hydraulic fluid cannot be removed from the cylinder fast enough because it must be directed along the return line to a non-pressurized tank of the system. The return line creates back pressure and the impact which is performed with compressed gas stays inefficient to a certain extent. The flow resistances of the return line thus create a problem when sudden back flow of the hydraulic fluid is required.

The above mentioned solution has also the disadvantage that the device becomes broad when the cylinders are located at the sides of the movable mass. The forces directed to the mass must be directed from the cylinders in sideways with the help of special arms in which case the arms become very heavy. It is difficult to make guide bars which direct the motion for the mass because the cylinders are located at the same place outside the mass. Each cylinder requires its own valve because the valves must be installed as close to the cylinder as possible. Further it is difficult to get efficient cooling to the gas spaces located in the cylinders. With the hammering apparatus according to the invention essential improvements can be achieved to the known prior art and it is characteristic of the invention that during the impact of the mass the hydraulic fluid coming from the cylinder space of the first cylinder or a part of it can be directed to an expanding space inside the piston rod with the help of a valve arrangement in which case a harmful back pressure caused by the hydraulic fluid being removed from the front of the piston is essentially reduced.

The advantage of the invention is the fact that during the acceleration of the mass the back pressure caused by the hydraulic fluid being removed suddenly from the cylinder can be essentially reduced when it can be directed for a while to a nearby space expanding exactly at the same time. When the mass is being lifted up to be effective, the hydraulic fluid is removed from this space to the return line but its removal does not have to be sudden. Thus in the invention a breathing space is created to the hammering apparatus which space receives pressure fluid at the same time as the impacts occur and removes it at the right time.

With the help of the structure according to the invention also the forces moving the mass can be organized in the back of the mass in order to affect at the same line on which the mass is moving, too. Further an efficient cooling can be achieved to the cylinder spaces in which the gas becomes warmer due to compression when a changing hydraulic fluid which has a lower temperature circulates behind a wall which conducts warmth well and cools gas spaces through the wall. With the hammering apparatus one can utilize a lot piston strokes which deviate from each other and the one can utilize movements of the mass when the mass can be lifted even to its highest position without the gas being squeezed excessively although also a pre-pressure would be set for the gas.

In the following the invention is described more detailed by referring to the accompanying drawings in which

Figure 1 shows a device according to the invention as a side view.

Figure 2 shows the device of the figure 1 to which impact mass and the structures required by it have been added.

In the figure 1 a hammering apparatus is shown from which a hollow arm 1 coming out functions both as a lifting arm when the impact mass is being lifted up and when the mass impacts to it it functions as an arm conveying accelerating force. At the end of the arm 1 there is an attaching part 9 with which it is attached to the impact mass. The arm 1 functions also as a piston rod for the piston 16 which is moved with hydraulic pressure. The hydraulic pressure is directed from the valve 15 along a pipe 14 to the front side (left side) of the piston 16. There is a cylinder space 4 at the backside (right side) of the piston 16 which cylinder space is restricted to be an annular space by an inner pipe 3. A cylinder liner 20 functions as its outer surface.

The piston 16 and the piston rod 1 slide sealed on top of the inner pipe. The cylinder space 4 is filled with gaseous nitrogen to an appropriate pre-pressure. Gaps 17 are directed from the cylinder space 4 to an annular space 5 located outside of it which annular space thus also functions as a store of the gaseous nitrogen and also becomes pressurized as the space 4 becomes pressurized due to the gaps 17. The outermost pipe 21 forms the outer surface of the annular space 5. When the gaseous nitrogen streams all the time through the gaps 17 to the annular space 5 and away from there when the hammering apparatus is at work , the hydraulic fluid directed to the annular space 6 cools efficiently the gaseous nitrogen which aims to become warmer due to continuous compression and a pressure decrease following it. The piston 16 performs the uplifting of the mass 10 and the cylinder space 6 located in front of it receives the pressurized hydraulic fluid along the pipe 14. During the impact the hydraulic fluid returns along the same pipe 14 as a very sudden burst. So that no back pressure would get created, the return liquid is directed to the inner space 2 of the inner pipe 3 with the help of a valve arrangement 15 which inner space is a space expanding at the very moment because the piston rod 1 moves outwards. Only a short pipe 14 with a relatively large diameter is left for the pressure fluid to run during the impact. Due to this the pressure fluid can be removed suddenly from the cylinder space 6. When the mass 10 is lifted up, the pressure fluid has more time to go away from the inner space 2 of the piston rod 1 and the inner pipe 3 to the return line. The changing pressure fluid located inside the inner pipe 3 also cools efficiently the compressible gas inside the cylinder space 4. In the figure 2 a hammering apparatus of the figure 1 is shown located to the right end of the shaft tube 19. The shaft tube 19 functions also as the control element of the impact mass 10 when the impact mass slides in the shaft tube 19 when the hammering apparatus lifts it up and accelerates it for the impact downwards. The impact mass 10 has a movement space 12. The impact mass 10 hits the piece 13. The whole hammering apparatus is attached for example to the end of the boom of an excavator from the part 11 attached to the shaft tube 17 when one works with it. With the help of an opened stage of the valve 15 shown by the figure 1 the length of the uplifting of the mass is adjusted.