GB1576566A - Electro-hydraulic percussive hand tool machine - Google Patents

Description

(54) AN ELECRO-HYDRAULIC PERCUSSIV AND TOOL MAcHINErn (71) We, ROBERT Bosca GmbH, a German company of Postfach SA 7000 Stuttgart, Germany, do hereby declare the invention, for which -we pray that a patent may be granted to us-, and the method by which it is to be performed, to be particularly described in and by the fdllowing statement: this invention is concerned with percussive hand tool machine, such as per cession hammers and drill hammers.

In our Spedfication 1,478,790 we have described and claimed a hand tool machine comprising an hydraulic motor for imparting a worlting movement to a tool, in which a tool driving Unit is arranged in the housing of the hand tool machine, the tool driving unit comprising a pump, a storage container from which pressure medium can be withdrawn by the pump, a valve through which pressure medium can be delivered by the pump to the hydraulic motor and an electric motor for driving the pump.

In the illustrated embodiments of that specification, the valve is a cylindrical rotary valve of rather complicated, and therefore expensive, construction.

We have now developed a simpler and more robust valve for such hand tool machines.

According to the present invention, we provide a percussive hand tool machine having a housing in which are located an hydraulic motor having as a moving part thereof an elongate striker displaceable along its longitudinal axis and which serves to impart a working movement to a tool, a pump, a storage container from - which pressure medium can be withdrawn by the pump, a valve through which pressure medium can be- delivered by the pump to the hydraulic motor, and an electric motor tor driving the pump, the valve consisting of an elongate control slide displaceable along its longitudinal axis, one end of which is acted upon by a spring and the other end of which is acted upon by a control pressure in such a manner that the control slide controls the pressure in two pressure spaces adjacent the ends of the striker, the pressure in one of the pressure spaces being con trilled through a non-return valve.

In order that the invention may be more fully understood, a preferred embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an elevation, partly in diagrammatic sectionj of an electro-hydraulic percussion hammer, and Figure 2 is a longitudinal section of the hydraulic motor and the control apparatus therefor of the apparatus of Figure 1.

The percussion hammer shown in Figure 1 comprises a housing 10 which is oval in cross-section. A tool - in this instance a chisel 12 i is held in a tool receiver 11 at the lower part of the hammer. Two handles 13, 14 are provided at the upper part of the housing perpendicu'lar to the axis of the chisel. Below the handle 13 there is a connecting union 15 for an electrical cable 16. An actuating lever 17 for a switch for the current supply line located in the handle 13, is arranged in the upper part of the handle 13.

In the upper part of the housing 10 there is an electric motor 18 which drives an hydraulic pump 20 through a drive 19 and a fan 21. The pump 20 is mounted in an oil reservoir 22 from which a pressure line 23 leads to an hydraulic unit which consists of a striker 24 which is the moving part of an hydraulic motor and a valve device which is shown in greater detail in Figure 2. An oil header tank 25 connected to the oil reservoir 22 is also located in the housing 10. The fan 21 sucks air through a duct 26 in the lower part of the housing and delivers it over the electric motor and the oil reservoir to an housing outlet 27.

Referring now to Figure 2, the striker 24 is sealingly slidingly guided in a bore 30.

Somewhat above its centre, it has an elon gate peripheral groove 31 provided with an upper control edge 311. Somewhat below this, there is a second peripheral groove 32 which is not so long as the groove 31. The shoulders on the peripheral groove 32 form control edges 321 and 3211. The flange 33 below the peripheral groove 32 has a conical end portion 34 which, at the lower limiting position of the striker 24, enters a cylindrical space 35. An annular groove 36, which forms a lower pressure space 37, is present in the bore 30 above and in communication with the space 35.

An annular groove 40, which froms an upper pressure space 41, is likewise located in the upper part of the bore 30. This is connected directly to a pressure accumulator 42 which has a fluid chamber 43 which is separated by a flexible separating wall 44 from a - gas chamber 45 containing a gas under high pressure. The separating wall 44 is fixed two the wall of the pressure accumulator by a retaining member 46.

The pump 20. delivers pressure medium into a duct 47 which opens into a slide bore 48 in which' a control slide 49 is sealingly slidingly guided. The latter has an elongate peripheral groove 50, the shoulders 501 and 501l of which form control edges.

A compression springs 51 acts on the control slide ;49 from below, the spring 51 being located in the, lower part 52 of'the slide bore from which a discharge duct 53 leads to the oil reservoir 22. A branch duct 54 from the discharge duct 53 opens into the slide bore 48. Its opening is below that of a duct 55 which leads from the slide bore 48 to the annular groove 36. A duct 56 leads from the upper part of the slide bore 48 in the bore 30.

A' duct 57, which leads to the inlet to a pressure limiting valve 58, branches from the duct 47. An outlet 59 from the pressure limiting valve is connected to the discharge duct '53.

A A duct 60 branches from the duct 56 and leads to a non-return valve 61 from the outlet, of which a duct 62 leads to the annular groove 40 in the bore '30. A branch 63 from the duct 62 leads directly to the bore, '30.

A discharge duct 64 which, like the discharge duct 53 leads to the oil reservoir, proceeds from a position above the annular groove 36. A duct 65 which opens into the bore 30 just below the annular groove 40 is connected to the discharge duct 64. The non-return valve 61 and the pressure limiting valve 58 are noted upon by springs 66 and 67 respectively. Their spring chambers nve connected to the oil reservoir through lines 68 and 69 respectively..

The, position of the striker 24 illustrated in'Figure 2 corresponds to the end of its working stroke and is a little above its lower limiting position. The pressure medium de livered by the pump 20 arrives in the slide bore 48 through the. duct 47 and in the pressure space 37 through the duct 55. The fluid pressure acting on the flange 33 pushes the striker 24 upwards towards the pressure accumulator 42.

At the instant at which the branch duct 65 is closed by the upper edge 241 of the striker 24, pressure begins to build up in the presusre space 41 and at the same time in the pressure accumulator 42. Near the upper limiting position of the upwardly moving striker 24, the branch duct 63 is opened by the control edge 311 on the peripheral groove 31, whereupon the pres sure prevailing in the pressure accumulator 42 can be built up in the peripheral groove 31 through the duct 62. This pressure ex tends through the duct 56 also to the upper end of the control slide 49 which is then moved rapidly downwards against the force of the spring 51.By the movement of the control slide 49, the pressure space 37 is relieved through the duct 55 and the peri pheral groove 50 to the duct 54 and thence to the discharge duct 53, that is to say the pressure'in the pressure space 37 collapses.

The high fluid pressure in the pressure accumulator 42 then acts on the striker 24 and the percussion stroke of the striker 24 begins. Thus, in this operating condition, the stored pressure as well as the delivery flow from the pump are available for the percussive stroke.

After a predetermined length of stroke, the upper edge 241 of the striker 24 opens the duct 65 whereupon a complete pressure relief of the system takes place immediately, that is to say the pressure in the pressure accumulator and in the pressure space 41 drops through the duct 65 to the discharge duct 64. The striker is thus relieved of hydraulic pressure shortly before the impact of the lower part 38 of the striker with the chisel 12.

Due to the just-described pressure relief of the entire system, the pressure on the upper part of the control slide 49 falls as well, whereupon the spring 51 displaces the control slide 49 into its upper limiting posi tion once again and the next working cycle can then begin.

Shortly before the striker 24 reaches its lowest limiting position -- it has then already struck the chisel 12 - the conical portion 34 extends into the cylindrical space 35 so that the final stage of the working move ment of the striker 24 is damped. In this so-called idling position of the striker, the pressure medium delivered substantially pressure-]ess by the pump 30 flows through the control slide 49 to the pressure 'space 37 and from there through the discharge duct 64 back to the oil reservoir

Claims (10)

WHAT WE CLAIM IS:

1. A percussive hand tool machine having a housing in which are located an hydraulic motor having as a moving part thereof an elongate striker displaceable along its longitudinal axis and which serves to impart a working movement to a tool, a pump, a storage container from which pressure medium can be withdrawn by the pump, a valve through which pressure medium can be delivered by the pump to the hydraulic motor, and an electric motor for driving the pump, the valve consisting of an elongate control slide displaceable along its longitudinal axis, one end of which is acted upon by a spring and the other end of which is acted upon by a control pressure in such a manner that the control slide controls the pressure in two pressure spaces adjacent the ends of the striker, the pressure in one of the pressure spaces being controlled through a non-return valve.

2. A machine according to claim 1, in which the control slide comprises an elongate peripheral groove bounded by two control edges and a third control edge which controls communication from the pump to the upper of the two pressure spaces through the non-return valve.

3. A machine according to claim 1 or 2, in which the striker is formed as a control element and comprises control edges which control communication to discharge ducts for the pressure medium.

4. A machine according to any of claims 1 to 3, in which the striker is slidably positioned in a bore and the bore is directly connected to an hydro-pneumatic pressure accumulator.

5. A machine according to claim 4, in which the two pressure spaces are formed as cylindrical spaces having a larger diameter than the striker bore and at each end of the latter.

6. A machine according to claim 5, in which a cylindrical space having a smaller diameter than the lower of the two pressure spaces is provided immediately below and in communication with the lower pressure space, the smaller diameter cylindrical space serving, in combination with a conical portion on the striker, as a damping space for the last portion of the working movement of the striker.

7. A machine according to any of claims 4 to 6, in which the pump delivers the pressure medium to a first duct which leads to the slide bore in which the control slide is positioned, the first duct being provided with a first branch duct which leads to a pressure limiting valve, and second and third ducts leads from the slide bore, the second duct leading to the lower of the two pressure spaces and the third duct leading to a central portion of the striker bore.

8. A machine according to claim 7, in which a second branch duct leads from the third duct to the non-return valve and the outlet side of the non-return valve is connected by a fourth duct to the striker bore, the fourth duct having a third branch duct therefrom leading to the upper of the two pressure spaces and the third branch duct being closed by the striker when it is in its upper limiting position.

9. A machine according to claim 7, in which there are first and second discharge ducts for the pressure medium, the first discharge duct being connected to the slide bore and to the pressure limiting valve and the second discharge duct being connected through two branches to the striker bore.

10. A percussive hand tool machine sub- stantially as herein described with reference to the accompanying drawings.