GB2394438A

GB2394438A - Pneumatically cushioned impact mechanism

Info

Publication number: GB2394438A
Application number: GB0324352A
Authority: GB
Inventors: Willy Braun; Axel Kuhnle
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2002-10-22
Filing date: 2003-10-17
Publication date: 2004-04-28
Anticipated expiration: 2023-10-17
Also published as: DE10249139A1; GB0324352D0; CN1496790A; CH696633A5; KR20040035566A; CN100352610C; GB2394438B

Abstract

A pneumatically cushioned impact mechanism for a machine tool, in particular for a drilling hammer or a chipping hammer, comprising an axially displaceable driving piston 10 for generating an impact energy, an axially displaceable impact body for delivering the impact energy to a tool, an air cushion situated between the driving piston 10 and the impact body for transmitting the impact energy from the driving piston 10 to the impact body as well as at least one control valve 18, 22, Fig 3a, (18', 20.1, 20.2, 22.1, 22.2) with a variable valve position for aerating and deaerating the air cushion. It is proposed that the valve position of the control valve Fig 3a, (18', 20.1, 20.2, 22.1, 22.2) is independent 18, 22 of the axial position of the impact body. The valve position is preferably dependent upon the axial position of the driving piston. Preferably, the driving piston has an axially continuous ventillation bore 20, wherein the control valve has a rotary slide valve which is keyed (Fig 1d) to the connecting rod 12.

Description

Pneumatically cushioned impact mechanism Prior art

5 The invention proceeds from a pneumatically cushioned impact mechanism according to the preamble of claim 1.

In conventional electropneumatic drilling or chipping hammers the impact energy is generated by a so-called 10 pneumatically cushioned impact mechanism. The pneumatically cushioned impact mechanism substantially comprises a cylindrical tube, a driving piston movable axially in the tube as well as an impact body ("striker") likewise movable axially in the tube, wherein enclosed in 15 the tube between the driving piston and the impact body is an air cushion, which transmits the impact energy from the driving piston to the impact body and uncouples the impact body mechanically from the driving piston.

20 The driving piston in said case is driven via a connecting rod by a crankshaft, which is rotated by an electric motor, so that the driving piston in the tube executes an axially oscillating motion.

25 Absolutely leakage-free sealing of the air cushion between the impact body and the driving piston is impossible in said case, with the result that in order to compensate the leakage losses and maintain the impact mechanism function aeration and deaeration of the air cushion is required.

30 For this purpose there are disposed in the wall of the tube in the region of the air cushion compensating bores, which in dependence upon the axial position of the impact body and of the driving piston are cleared or closed and consequently enable aeration and deaeration of the air

cushion. In the known pneumatically cushioned impact mechanisms aeration and deaeration of the air cushion is therefore controlled by the impact body and possibly also by the driving piston.

Advantages of the invention In contrast, the invention provides a pneumatically cushioned impact mechanism, in which for aeration and 10 deaeration of the air cushion a control valve is provided, wherein the valve position of the control valve is independent of the axial position of the impact body.

Instead, the valve position is preferably dependent upon the axial position of the driving piston.

Thus, in the event of a change in operating conditions due to different tools, various workpieces or altered impact frequencies the air quantity contained in the air cushion may also be controlled to suit requirements.

In a preferred embodiment of the invention the driving piston has at least one axially continuous ventilation bore for aerating and deaerating the air cushion, wherein the control valve has a rotary slide valve, which is disposed 25 in the driving piston and which in dependence upon its rotary position clears or closes the ventilation bore. In said case, therefore, aeration and deaeration of the air cushion enclosed between the driving piston and the impact body is effected in axial direction through the driving 30 piston, for which purpose the axially continuous ventilation bore is used. The control valve for aeration and deaeration in the present case substantially comprises

a rotary slide valve, which is disposed in the driving piston and which in dependence upon its rotary position clears or closes the ventilation bore.

5 The driving piston is preferably connected by a connecting rod to a rotatable crankshaft, wherein the rotary slide valve of the control valve is connected non-rotatably to the connecting rod so as to be rotatable about an axis of rotation parallel to the crankshaft. The effect achieved 10 by said non-rotatable connection of the connecting rod to the rotary slide valve of the control valve is that the rotary slide valve is rotated by the connecting rod, so that the valve position of the control valve is dependent upon the crankshaft position. The non-rotatable connection 15 of the connecting rod to the rotary slide valve is preferably achieved by means of a keyed connection.

In a preferred embodiment of the invention the connecting rod is mounted via a piston pin in a piston boss of the 20 driving piston, wherein the piston pin forms the rotary slide valve of the control valve. The piston pin in said case therefore has two technical functions, namely, on the one hand, mechanical support of the connecting rod in the piston boss of the driving piston and, on the other hand, 25 control of the aeration and deaeration of the air cushion, in that the piston pin forms the rotary slide valve of the control valve. During operation of the pneumatically cushioned impact mechanism according to the invention the piston pin is therefore rotated by the connecting rod, 30 wherein the piston pin acts as a rotary slide valve and in dependence upon its rotary position clears or closes the ventilation bore in the driving piston.

In order to fulfil its function as a rotary slide valve, in the piston pin there is preferably disposed a radially continuous valve bore, which in specific rotary positions 5 of the piston pin forms a component of the ventilation bore in the driving piston and therefore enables aeration or deaeration of the air cushion.

Preferably, for sealing the piston pin at least one seal is 10 provided, wherein the seal advantageously surrounds the piston pin in an annular manner. Preferably, however, two seals are provided for sealing the piston pin and are disposed in each case laterally adjacent to the radially extending valve bore in the piston pin.

The rotary slide valve and/or the driving piston moreover preferably has oblong holes, which extend over a preset length parallel to the axis of rotation of the rotary slide valve, wherein the length of the oblong holes is greater 20 than the extension in peripheral direction. In said manner, even upon small rotational movements of the rotary slide valve an adequate ventilation cross section is achieved. 25 In an advantageous variant of the invention two axially continuous ventilation bores are disposed in the driving piston, wherein the rotary slide valve in dependence upon its rotary position clears or closes the two ventilation bores. In said case, the two ventilation bores may in dependence upon the rotary position of the rotary slide valve be

cleared or closed to an identical extent, so that by virtue of the additional ventilation bore only the effective ventilation cross section is enlarged. In said case, the dependence of the ventilation cross section cleared by the 5 control valve upon the position of the driving piston and/or the crankshaft angle is therefore cophasal for the two ventilation bores, so that both ventilation bores are opened and/or closed simultaneously.

10 It is however alternatively also possible for the two ventilation bores to be cleared or closed to a differing extent in dependence upon the rotary position of the rotary slide valve, so that a change of the aeration behaviour is effected by means of the additional ventilation bore. In 15 said case, the dependence of the ventilation cross section cleared by the control valve upon the position of the driving piston and/or the crankshaft angle is therefore phase-displaced for the two ventilation bores, so that both ventilation bores are opened and/or closed in a staggered 20 manner. Said staggered control leads to a smoother response characteristic during opening and closing for aeration and/or deaeration.

Thus, during opening of the control valve at first only one 25 of the two ventilation bores is opened, while the other ventilation bore is initially still closed. After a preset delay time and a corresponding change in the position of the driving piston and/or of the crankshaft the second ventilation bore is then also opened, with the result that 30 the effective ventilation cross section assumes its maximum value.

In a corresponding manner, during closing of the control valve at first only one of the two ventilation bores is closed, while the other ventilation bore initially remains open. After a preset delay time and a corresponding change 5 in the position of the driving piston and/or of the crankshaft the second ventilation bore is then also closed, with the result that the effective ventilation cross section is zero.

10 By virtue of said step-by-step opening and/or closing of the control valve and the smoother response characteristic associated therewith pressure surges and resonance effects in the air cushion are extensively avoided.

15 The control valve is preferably at least temporarily closed in a compression phase of the driving piston and at least temporarily open in a decompression phase of the driving piston. 20 For example, the control valve during the decompression phase of the driving piston is open from a crankshaft angle, which lies between 0 and 30 after the top dead centre of the driving piston, wherein a value of 10 has proved particularly advantageous.

The control valve, on the other hand, during the decompression phase of the driving piston is preferably closed from a crankshaft angle, which lies between 30 and 0 before the bottom dead centre of the driving piston, 30 wherein a value of 10 has proved particularly advantageous.

During the compression phase of the driving piston, on the other hand, the control valve is preferably permanently closed in order to enable the driving piston to transmit its impact energy via the air cushion to the impact body.

Both the driving piston and the impact body are preferably disposed in an axially displaceable manner in a stationary tube, so that the air cushion is enclosed in the tube between the impact body and the driving piston.

It is however alternatively also possible for the driving piston to be designed as a so-called barrel piston, in which the impact body is axially displaceable. Such a barrel piston comprises a tube, which is closed at one end and in which the impact body is disposed in an axially displaceable manner. Upon an axial relative movement between the barrel piston and the impact body the air cushion in the barrel piston is therefore compressed and/or decompressed. The invention moreover also comprises a machine tool, in particular a drilling hammer or a chipping hammer, having a pneumatically cushioned impact mechanism according to the invention. Finally, the invention also comprises a driving piston developed according to the invention for a pneumatically cushioned impact mechanism of the previously described type. Drawings

Further advantages arise from the following description of

the drawings. In the drawings two embodiments of the invention are illustrated. The drawings, the description

5 and the claims contain numerous features in combination.

The person skilled in the art will advantageously consider the features also individually and combine them into meaningful further combinations.

10 The drawings show: Fig. la a sectional view of a driving piston according to the invention for a pneumatically cushioned impact mechanism, 15Fig. lb a sectional view of a crankshaft for driving the driving piston, Fig. lc a sectional side view of the driving piston along the line A-A in Figure la, Fig. Id another sectional side view along the line 20C-C in Figure la, Fig. 2a the sectional view from Figures la and lb with a different piston position, Fig. 2b a sectional view along the line A-A in Figure 2a, 25Fig. 2c the sectional view along the line C-C in Figure 2a, Fig. 3a the sectional view from Figure la with another embodiment of a driving piston, Fig. 3b a sectional view of a crankshaft for driving 30the driving piston of Figure 3a, Fig. 3c a sectional side view along the line A-A in Figure 3a and

Fig. 3d another sectional side view along the line C-C in Figure 3a.

Description of the embodiments

The sectional views in Figures la, lc and Id as well as 2b - 2c show a driving piston 10, which is used in a pneumatically cushioned impact mechanism of a drilling hammer and is axially displaceable there in a tube in order 10 to drive an impact body, which is likewise disposed in an axially displaceable manner in the tube.

The driving piston 10 is driven via a connecting rod 12 and a cam disc 14 by a crankshaft 16, which is rotated by an 15 electric motor, wherein for the sake of simplicity the electric motor is not illustrated. The pistonside end of said connecting rod 12 is mounted by means of a piston pin 18 in a piston boss of the driving piston 10. Upon rotation of the crankshaft 16 the driving piston 10 20 therefore executes an axially oscillating motion in the tube of the drilling hammer.

In said case, the driving piston 10 acts upon an air cushion, which is enclosed in the tube between the driving 25 piston 10 and the impact body. The air cushion is therefore alternately compressed and decompressed, with the result that the kinetic energy of the driving piston 10 is transmitted in a mechanically uncoupled manner to the impact body, which therefore likewise executes an axially 30 oscillating motion in the tube and, in so doing, delivers impacts onto the tool shank.

Absolutely leakage-free sealing of the air cushion between the impact body and the driving piston 10 is however impossible so that in order to compensate the leakage losses and maintain the impact mechanism function aeration 5 and deaeration of the air cushion is required.

For said purpose there is disposed in the driving piston 10 an axially continuous ventilation bore 20, through which air may escape from the air cushion or penetrate into the 10 air cushion. The ventilation bore 20 emanates from the two end faces of the driving piston 10 and opens internally into the piston boss, in which the piston pin 18 is rotatably mounted.

15 Said aeration and deaeration of the air cushion is in this case controlled by a control valve, which is formed substantially by the piston pin 18 and which in dependence upon its rotary position clears or blocks the ventilation bore 20. The piston pin 18 therefore has an - in relation 20 to its axis of rotation - radially continuous valve bore 22, wherein the valve bore 22 in the rotary position of the piston pin 18 shown in Figure lo opens into the ventilation bore 20 on both sides and therefore clears the latter. In the rotary position of the piston pin 18 shown in Figure 25 2b, on the other hand, the ventilation bore 20 is closed by the lateral surface of the piston pin 18, so that no aeration or deaeration of the air cushion is possible.

For sealing the point of contact between the lateral 30 surface of the piston pin 18 having the mouth openings of the valve bore 22 disposed therein and the inner surface of the piston boss having the mouth openings of the

ventilation bore 20 disposed therein two sealing rings 24.1, 24.2 are provided, which surround the piston pin 18 in an annular manner and are disposed on either side of the valve bore 22.

Rotation of the piston pin 18 into the desired position is effected in the present case by the connecting rod 12 and hence in dependence upon the angular position of the crankshaft 16. For said purpose, the piston- side end of 10 the connecting rod 12 is non-rotatably connected to the piston pin 18, so that the piston pin 18 rotates with the connecting rod 12. The non-rotatable connection between the connecting rod 12 and the piston pin 18 is achieved in that the piston-side end of the connecting rod 12 has a 15 hexagon socket, as may be seen from Figure Id. The piston pin 18 in the region of the hexagon socket has a suitably adapted hexagonal external shape, so that the piston pin 18 is key-connected to the connecting rod 12.

20 Figures la to Id show the driving piston 10 during the decompression phase at a crankshaft angle a=90 , wherein the crankshaft 16 with the cam disc 14 is rotating in an anticlockwise direction. From Figure lc it is evident that the valve bore 22 during the decompression phase opens the 25 ventilation bore 20 from a crankshaft angle aOpEN=10 and closes it again from a crankshaft angle of acTosED=l7oo.

Figures 2a to 2c, on the other hand, show the driving piston 10 during the compression phase at a crankshaft 30 angle a=270 , wherein the crankshaft 16 with the cam disc 14 is likewise rotating in an anticlockwise direction.

From Figure 2b it is evident that the piston pin 18 closes

the ventilation bore 20 during the entire compression phase, so that during the compression phase no aeration or deaeration of the air cushion is possible. This is practical in order to enable the driving piston 10 to 5 transmit its kinetic energy via the air cushion to the impact body.

As the embodiment illustrated in Figures 3a to 3d corresponds substantially to the previously described 10 embodiment, to avoid repetition reference is made to the previous description and in the following the reference

characters used for functionally identical components are the same, only marked by an apostrophe for the purpose of differentiation. A characteristic feature of this embodiment is that two ventilation bores 20.1, 20.2 are disposed in the driving piston 10' in order to enlarge the effective ventilation cross section.

The two ventilation bores 20.1, 20.2 emanate in each case from the two opposite end faces of the driving piston 10' and open internally into the piston boss, in which the piston pin 18' is rotatably mounted.

There are accordingly two valve bores 22.1, 22.2 disposed in the piston pin 18', wherein the valve bore 22.1 in dependence upon the rotary position of the piston pin 18' clears or closes the ventilation bore 20.1, while the valve 30 bore 22.2 in dependence upon the rotary position of the piston pin 18' clears or closes the ventilation bore 20.2.

Said two valve bores 22.1, 22.2 are disposed in the piston pin 18' in a radially continuous manner at the same angle in relation to the axis of rotation of the piston pin 18'.

This means that the two valve bores 22.1, 22.2 in 5 dependence upon the rotary position of the piston pin 18' simultaneously clear and block the associated ventilation bores 20.1, 20.2. The dependence of the effective opening cross section of aeration or deaeration upon the crankshaft angle is therefore cophasal for the two ventilation bores 10 20.1, 20.2.

The invention is not restricted to the previously described preferred embodiments. Rather, a number of variants and modifications are possible, which likewise make use of the 15 inventive idea and therefore fall within the protective scope.

R.303366

11 October 2002 5 ROBERT BOSCH GMBH; D-70442 Stuttgart Reference characters 10, 10' driving piston 12, 12' connecting rod 14, 14' cam disc 16, 16' crankshaft 18, 18' piston pin 20, 20.1, 20.2 ventilation bore 22, 22.1, 22.2 valve bore 24.1, 24.2, 24.1', 24.2', sealing ring 24.3', 24.4'

crankshaft angle

Claims

1. Pneumatically cushioned impact mechanism for a machine tool, in particular for a drilling hammer or a 5 chipping hammer, comprising an axially displaceable driving piston (10, 10') for generating an impact energy, an axially displaceable impact body for delivering the impact energy to a tool, an air cushion situated between the driving piston (10, lo') and the 10 impact body for transmitting the impact energy from the driving piston (10, 10') to the impact body as well as at least one control valve (18, 18', 20, 20.1, 20.2, 22, 22.1, 22.2) with a variable valve position for aerating and deaerating the air cushion, 15 characterized in that the valve position of the control valve (18, 18', 20, 20.1, 20.2, 22, 22.1, 22.2) is independent of the axial position of the impact body.

20

2. Pneumatically cushioned impact mechanism according to claim 1, characterized in that at least one axially continuous ventilation bore (20, 20.1, 20.2) is disposed in the driving piston (10, 10') for aerating and/or deaerating the air cushion, wherein the control 25 valve (18, 18', 20, 20.1, 20.2, 22, 22.1, 22.2) comprises a rotary slide valve (18, 18'), which is disposed in the driving piston (10, 10') and which in dependence upon its rotary position clears or closes the ventilation bore (20, 20.1, 20.2).

3. Pneumatically cushioned impact mechanism according to claim 2, characterized in that the driving piston

(10, 10') is connected by a connecting rod (12, 12') to a rotatable crankshaft (16, 16'), wherein the rotary slide valve (18, 18') of the control valve (18, 18', 20, 20.1, 20.2, 22, 22.1, 22.2) is non 5 rotatably connected to the connecting rod (12, 12') so as to be rotatable about an axis of rotation parallel to the crankshaft (16, 16').

4. Pneumatically cushioned impact mechanism according to 10 claim 2 and/or claim 3, characterized in that the connecting rod (12, 12') is mounted by means of a piston pin (18, 18') in a piston boss of the driving piston (10, 10'), wherein the piston pin (18, 18') forms the rotary slide valve of the control valve 15 (18, 18', 20, 20.1, 20.2, 22, 22.1, 22.2).

5. Pneumatically cushioned impact mechanism according to claim 4, characterized in that for sealing the piston pin (18, 18') at least one seal (24.1 - 24.4) is 20 provided.

6. Pneumatically cushioned impact mechanism according to at least one of the preceding claims, characterized in that disposed in the rotary slide valve (18, 18') is 25 an - in relation to its axis of rotation - radially continuous valve bore (22, 22.1, 22.2).

7. Pneumatically cushioned impact mechanism according to at least one of the preceding claims, characterized in 30 that two axially continuous ventilation bores (20.1, 20.2) are disposed in the driving piston (10, 10') and the rotary slide valve (18, 18') in

dependence upon its rotary position clears or closes the two ventilation bores (20.1, 20.2).

8. Pneumatically cushioned impact mechanism according to 5 claim 7, characterized in that the rotary slide valve (18, 18') in dependence upon its rotary position clears or closes the two ventilation bores (20.1, 20. 2) to a differing extent.

10

9. Pneumatically cushioned impact mechanism according to claim 7, characterized in that the rotary slide valve (18, 18') in dependence upon its rotary position clears or closes the two ventilation bores (20.1, 20. 2) to an identical extent.

10. Pneumatically cushioned impact mechanism according to at least one of the preceding claims, characterized in that the control valve (18, 18', 20, 20.1, 20.2, 22, 22.1, 22.2) is at least temporarily closed in a 20 compression phase of the driving piston (10, 10') and at least temporarily open in a decompression phase of the driving piston (10, 10').

11. Pneumatically cushioned impact mechanism according to 25 claim 10, characterized in that the control valve (18, 18', 20, 20.1, 20.2, 22, 22. 1, 22.2) during the decompression phase of the driving piston (10, 10') is open from a crankshaft angle (a), which lies between 0 and 30 after the top dead centre of the driving 30 piston (10, 10').

12. Pneumatically cushioned impact mechanism according to claim 10 and/or claim 11, characterized in that the control valve (18, 18', 20, 20.1, 20. 2, 22, 22.1, 22.2) during the decompression phase of the driving 5 piston (10, 10') is closed from a crankshaft angle (a), which lies between 30 and 0 before the bottom dead centre of the driving piston (10, 10').

13. Driving piston for a pneumatically cushioned impact mechanism according to at least one of the preceding claims.

14. Machine tool, in particular a drilling hammer or chipping hammer, having a pneumatically cushioned 15 impact mechanism according to at least one of claims 1 to 12.

15. A pneumatically cushioned impact mechanism substantially as herein described with reference to 20 the accompanying drawings.

16. A driving piston substantially as herein described with reference to the accompanying drawings.

25

17. A machine tool substantially as herein described with reference to the accompanying drawings.