GB2145959A - Air-spring percussive tool - Google Patents

Abstract

An air-spring percussive tool comprises a casing (1) in which are accommodated a drive (2), a working tool (3), a cylinder (4) having air replenishing ports (11, 12, 13, 14). The cylinder (4) accommodates a piston (5) connected to the drive (2) and a hammer piston (6). The air-spring percussive tool also has a sleeve (17) surrounding the cylinder (4) and having an element for selectively uncovering the air replenishing ports (11, 12, 14) of the cylinder (4) when the sleeve (17) is displaced. The replenishing air ports (11, 12, 14) are disposed in one and the same plane drawn at right angles to the axis of the cylinder (4). <IMAGE>

Description

SPECIFICATION Air-spring Percussive Tool The invention relates to the mechanical engineering, and in particular, to an air-spring percussive tool.

The invention may be used in the mechanical engineering and other industries for making holes in rocks and construction materials and for demolishing such materials.

Known in the art is an air-spring percussive tool (cf. FRG patent No. 2938513, September 1979), comprising a casing in which are accommodated a drive, a working tool, a cylinder in which is installed a piston connected to the drive and a hammer piston coupled to the piston by an air spring and cooperating with the working tool. The piston is connected to a connecting rod which is mounted on a crank pin installed in a rotary case having a shaft operatively connected to a bevel gearing. This air-spring percussive tool also comprises friction members secured to the casing and braking the bevel gearing. The friction force at the braking members depends on the feed force applied to the tool casing during cooperation.

The greater is the feed force, the stronger is the cohesion between the friction members which reduces their slippage and results in an increase in the blow rate of the hammer piston. Energy of a single blow of the hammer piston also increases with the increase in the blow rate in the air-spring percussive tool. This air-spring percussive tool is, however, rather unreliable owing to continuous wear of the friction members, and this results in a narrow range of control of impact energy of the hammer piston.

Known in the art is an other air-spring percussive tool (cf. US patent No. 1402727, January 3, 1972), comprising a casing, accommodating a drive, a working tool, a cylinder having air replenishing ports in which are installed a piston connected to the drive, and a hammer piston coupled to the piston by means of an air spring and cooperating with the working tool, and a sleeve surrounding the cylinder and movable relative thereto, the sleeve having element is adapted to selectively uncoverthe air replenishing ports when the sleeve is displaced.

In order to provide for impact energy control, the sleeve in this prior art tool is mounted for axial movement relative to the cylinder and is biased by a spring. The element of the sleeve adapted for selectively uncovering the air replenishing ports of the cylinder is made in the form of a plurality of ports disposed axially along the sleeve.

When a force is applied to the tool casing, this force overcomes the force of the spring, and the sleeve is caused to move axially along the cylinder.

The movement of the sleeve with respect to the cylinder results in the ports of the sleeve being successively brought in registry with the air replenishing ports which are located at different levels in the cylinder. Maximum impact energy of the hammer piston is achieved when the air spring communicates with atmosphere through the top air replenishing port which is disposed under the working end face of the piston when the piston is at the lower dead centre. The hammer piston impact energy is lowered when the air spring communicates with atmosphere not only through the top air replenishing port but also through another air replenishing port of the cylinder which is below the top air replenishing port.In such case the total area of the air replenishing ports becomes greater so that the amount of pressure reduction (or vacuum) in the air spring during the movement of the piston away from the hammer piston decreases thus resulting in a shorter return stroke of the hammer piston. When the piston moves toward the hammer piston, air losses from the air spring increase thus resulting in a lower velocity of the hammer piston moving in the direction toward the working tool. A decrease in the velocity of the hammer piston results in lower impact energy of the hammer piston.

Further increase in the feed force applied to the casing of the tool results in that the air spring is connected to atmosphere through one or more air replenishing port which is also below the top air replenishing port. This will result in a still greater increase in the total area of the air replenishing ports and still greater decrease in impact energy of the hammer piston. The range of impact energy control in such a tool is not sufficiently wide.

During operation of the tool, the open air replenishing port which is spaced from the top air port is prematurely covered by the piston if this air replenishing port is above the top air replenishing port or by the hammer piston if this air replenishing port is below the top air replenishing port. The time during which the air spring communicates with atmosphere through this air replenishing port during intervals between two successive blows of the hammer piston decreases so that this air replenishing port cannot be used to the full extent for lowering impact energy of the hammer piston.It should be noted that the greater is the distance from such air replenishing port to the top air replenishing port, the shorter is the time during which it is used for connecting the air spring to atmosphere during an interval between two successive blows and the smaller is its effect on reduction of impact energy.

All this does not make it possible to achieve a wide-range control of impact energy.

It is an object of the invention to provide an air-spring percussive tool having a wider range of control of impact energy of the hammer piston of the tool.

The invention essentially consists in that in an air-spring percussive tool, comprising a casing accommodating a drive, a working tool, a cylinder which has air replenishing ports and in which are installed a piston connected to the drive and a hammer piston which is coupled to the piston by means of an air spring and which cooperates with the working tool, and a sleeve surrounding the cylinder and movable with respect thereto, the sleeve having an element for selectively uncovering the air replenishing ports of the cylinder when the sleeve is displaced, according to the invention, the air replenishing ports are made in one and the same plane drawn at right angles to the cylinder axis.

The provision of an air-spring percussive tool with a cylinder in which the air replenishing ports are made in one and the same plane drawn at right angles to the cylinder axis makes it possible to use each ofthe air replenishing ports during a necessary working time interval so that impact energy of the hammer piston can be reduced over a wider range.

The sleeve may be mounted for rotation with respect to the cylinder, and the element for selectively uncovering the air replenishing ports comprises portions of the sleeve wall. This makes it possible to reduce the size of the air-spring percussive tool, hence to lower its weight.

The sleeve may be mounted in a fixed relationship to the casing, with the cylinder mounted for rotation about its own axis, the element for selectively uncovering the air replenishing ports comprising portions of the sleeve wall. This makes it possible to improve reliability of the tool.

The sleeve may be made integral with the casing and the element for selectively uncovering the air replenishing ports comprises a portion of the casing wall between grooves thereof. This construction of the sleeve provides for facilitating the manufacturing process.

The sleeve may be mounted for axial movement with respect to the cylinder and the element for selectively uncovering the air replenishing ports may be in the form of a bevel cut of the sleeve wall.

The sleeve may also be mounted for axial movement with respect to the cylinder and the element for selectively uncovering the air replenishing ports may be made in the form of a row of circumferentially spaced ports, the dimension of the ports in the axial direction along the sleeve progressively increasing from one port to another.

With this construction of the sleeve the manufacture of the sleeve is facilitated since the sleeve has an annular groove for cooperation with an eccentric pin.

A large range of impact energy control of the hammer piston is achieved in this air-spring percussive tool, which makes it possible to improve productivity of drilling with hammer drills independent of the strength of a material being drilled and makes the air-spring percussive tool more reliable.

The invention will now be described with reference to specific embodiments of an air-spring percussive tool illustrated in the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of an air-spring percussive tool with a sleeve mounted for rotation relative to the cylinder, according to the invention; Figure 2 is a transverse sectional view of the air-spring percussive tool taken along the line Il-Il in Figure 1 with one uncovered air replenishing port, according to the invention; Figure 3 is a transverse sectional view of the air-spring percussive tool taken in the plane of air replenishing ports with two uncovered air replenishing ports, according to the invention;; Figure 4 is a transverse sectional view of an air-spring percussive tool taken in the plane of air replenishing ports with a sleeve installed in a fixed relationship to the casing and with the cylinder mounted for rotation about its own axis, according to the invention; Figure 5 is a transverse sectional view of an air-spring percussive tool taken in the plane of air replenishing ports with a sleeve integral with the casing, according to the invention; Figure 6 is a detail of an air-spring percussive tool having a cylinder with air replenishing ports and a sleeve with an element for selectively uncovering air replenishing ports which comprises a bevel cut in the sleeve wall, according to the invention:: Figure 7 is a detail of an air-spring percussive tool having a cylinder with air replenishing ports and a sleeve with an elementfor selectively uncovering air replenishing ports comprising a row of circumferentially spaced ports, the dimension of the ports in the axial direction along the sleeve progressively increasing from one port to another, according to the invention; Figure 8 is a diagram illustrating operation of an air-spring percussive tool with controlled impact energy, according to the invention.

An air-spring percussive tool has a casing 1 (Figure 1) which accommodates a drive 2, a working tool 3, a cylinder4 in which are installed a piston 5 connected to the drive 2 and a hammer piston 6, both the piston and hammer piston having seals 7 and 8, respectively. The hammer piston 6 is coupled to the piston 5 by means of an air spring 9 and cooperates with the working tool 3 at regular intervals in sympathy with the movement of the piston 5. Air replenishing ports 11,12, 13 (Figure 2) and 14 (Figure 1) are made in the cylinder 4 under the working end face of the piston 5 when the piston is at the lower dead centre position, the air replenishing ports being made in one and the same plane drawn at right angles to the axis of the cylinder 4.A port 15 disposed underthe end face 16 of the hammer piston 6 when it is in the working position and touches the working tool 3 is also made in the cylinder 4. A sleeve 17 surrounding the cylinder is disposed in the zone of the air replenishing ports 11,12,13 (Figure 2) and 14 (Figure 1). The sleeve 17 has a groove 18 for cooperation with an eccentric pin 19 of a knob 20 mounted in the casing 1.

The sleeve 17 is mounted for rotation with respect to the cylinder 4.

In Figure 11 is the distance from the air replenishing port 11 to the end face 16 of the hammer piston 6 which is in the working position when it touches the working tool 3.

The sleeve 17 (Figure 2) has ports 21,22,23,24, and an element for selectively uncovering the air replenishing ports 11,12,13, 14ofthecylinder4 comprises portions 25,26,27,28 of the wall of the sleeve 17 which are separated by ports 21,22,23,24 of the sleeve 17. The air replenishing port 11 is an open port. In Figure 3 the air replenishing ports 11 and 12 are open.

In case the sleeve 17 (Figure 4) is fixed with respect to the casing 1, the cylinder 4 is made with a groove 29 for cooperation with the eccentric pin 19 of the knob 20 for turning the cylinder about its own axis. The element for selectively uncovering the air replenishing ports 11, 12, 13, 14 is also made in the form of portions 25,26,27,28 of the sleeve 17.

When the sleeve 17 is made integral with the casing 1 (Figure 5), the casing is made with grooves 30,31, 32,33 which are disposed similarly to the ports 21 (Figure 2) 22,23, 24 of the sleeve 17, when the sleeve is mounted for rotation with respect to the cylinder 4. The cylinder 4 has a groove 34 (Figure 5) for cooperation with the eccentric pin 19 of the knob 20. The element for selectively uncovering the air replenishing ports 11,12,13, 14 comprises portions of the wail of the casing 1 between its grooves 30, 31,32,33.

When the sleeve 17 (Figure 6) is mounted for axial movement with respect to the cylinder 4, an annular groove 35 is made in the sleeve for cooperation with the eccentric pin 19. The element for selectively uncovering the air replenishing ports 11, 12, 13, 14 is made in the form of a bevel cut 36 of the wall of the sleeve 17 or in the form of a row of circumferentially spaced ports 37 (Figure 7) 38, 39,40, the dimension of the ports in the axial direction along the sleeve 17 progressively increasing from one port to another, the ports being disposed in the zone of the air replenishing ports 11,12,13, l4ofthe cylinder 4.

Figure 8 shows a diagram illustrating operation of the tool, in which the following symbols are used; S, is the trajectory of the piston; S2 is the trajectory of the hammer piston when the air spring communicates with atmosphere through one of the air replenishing ports disposed in the plane drawn at right angles to the cylinder axis; Si2, is the trajectory of the hammer piston with two open air replenishing ports disposed in the plane drawn at right angles to the cylinder axis; S22 is the trajectory of the hammer piston with an open air replenishing port spaced from the first port axially along the cylinder in the direction toward the hammer piston; S23 is the trajectory of the hammer piston with an open air replenishing port spaced from the first port axially along the cylinder in the direction toward the piston;; I, is the distance from the end face of the hammer piston to the air replenishing port axially along the cylinder in the direction toward the hammer piston; 11 < 1; 12 is the distance from the end face of the hammer piston to the air replenishing port spaced from the first air replenishing port axially along the cylinder in the direction toward the piston; i2 > l1; a is the point on the trajectory S22 at which the hammer piston covers the air replenishing port spaced at the distance I,; b is the point on the trajectory S22 at which the hammer piston uncovers the air replenishing port spaced at the distance /,; c is the point on the trajectory S1 at which the piston uncovers the air replenishing port spaced at the distance /2;; d is the point on the trajectory S, at which the piston covers the air replenishing port spaced at the distance I,; t1 is the time during which the hammer piston, which moves along the trajectory S22, covers the air replenishing port spaced at the distance li; t2 is the time during which the piston covers during its movement the air replenishing port spaced at the distance I,; a is the angie of rotation of the drive.

The air-spring percussive tool functions in the following manner.

During the hammering operation, the hammer piston 6 (Figure 1) reciprocates in the cylinder 4 under the action of similar reciprocations of the piston 5 to which it is coupled through the air spring 9. The hammer piston 6 imparts blows to the working tool 3 at regular intervals. To compensate for air leakage from the air spring 9 during operation of the tool, there are provided air replenishing ports 11,12, 13 (Figure 2) and 14(Figure 1).

The air spring 9 is connected to atmosphere through one air replenishing port 11 of the cylinder 4 and also through the port 21 (Figure 2) of the sleeve 17.

In order to prevent wear of the seal 7 (Figure 1) of the piston 5 and seal 8 of the hammer piston 6, the diameter of the air replenishing port 11 must be as small as possible. For a stable operation of the air-spring percussive tool upon changes in the trajectory of the hammer piston 6 when dealing with workpiece materials of different strength, the air replenishing port 11 is spaced at a distance /from the end face 16 of the hammer piston 6.

The distance / is chosen in such a manner as to provide for maximum impact energy of the hammer piston 6 when it moves along the trajectory S2 (Figure 8).

When the piston 5 (Figure 1) moves away from the hammer piston 6, a pressure reduction occurs in the air spring 9 which is sufficient to raise the hammer piston 6 to a maximum possible height.

When the piston 5 moves toward the hammer piston 6, high pressure is built-up in the air spring 9 so as to cause the hammer piston 6 to move toward the working tool 3 at high velocity for imparting a blow (see the trajectory S2 in Figure 8).

The port 15 (Figure 1) made adjacent to the end face 16 of the hammer piston 6 has but a slight influence on operation of the tool during the hammering operation since the time during which it connects the air spring 9 to atmosphere is too short.

The port 15 is designed for a reliable transition of the tool from running to the hammering operation.

By turning the knob 20, the eccentric pin 19 cooperating with the groove 18 causes rotation of the sleeve 17, which is mounted on the cylinder 4 for rotation relative thereto, through an angle sufficient for bringing the port 22 (Figure 2) of the sleeve 17 in registry with the air replenishing port 12. This arrangement of the sleeve 17 for rotation with respect to the cylinder 4 is associated with the arrangement of the air replenishing ports 11,12, 13, 14 in one and the same plane drawn at right angles to the axis of the cylinder 4 so as to provide for uncovering of these ports. Therefore, the air replenishing port 12 disposed in the plane drawn at right angles to the axis of the cylinder 4 is uncovered, and the air spring 9 now communicates with atmosphere through the two air replenishing ports 11 and 12.In this case a lower pressure reduction is created in the air spring 9 when the piston 5 (Figure 1) moves away from the hammer piston 6, and the hammer piston 6 is raised to a smaller height, compared to the case when only one air replenishing port was uncovered. When the piston 5 moves toward the hammer piston 6, the velocity of the hammer piston moving toward the working tool 3 will be lower.

In this case impact energy is lowered by an amount determined by steepness of the trajectory S21 (Figure 8) of movement of the hammer piston 6 (Figure 1). With this position of the air replenishing port 12 the impact energy is lowered. Any other position of the air replenishing port 12 would result in a smaller reduction of impact energy of the hammer piston 6. Thus, should the air replenishing port be disposed at a distance li (Figure 8) smaller than I, this air replenishing port would be covered upon the rise of the hammer piston 6 (Figure 1) through this distance.During further movement of the hammer piston 6 along the trajectory S22 (Figure 8) from the point a to the point b only one air replenishing port 11 (Figure 1)would remain open, which is spaced at the distance ifrom the end face 16 of the hammer piston 6. The movement of the hammer piston 6 along the trajectory S22 (Figure 8) during the time t1 is accompanied by a higher pressure build-up in the air spring 9 (Figure 1). The higher pressure in the air spring 9 results in a more rapid reversal of direction of movement of the hammer piston 6 so that the hammer piston would acquire a greater velocity for hitting the working tool 3, hence a greater impact energy.

In case one more air replenishing port is uncovered, which is disposed at a distance smaller than /1 (Figure 8) from the hammer piston 6, the influence of such port on the reduction of impact energy of the hammer piston 6 (Figure 1) will be still smaller than the influence ofthe air replenishing port spaced at a distance li (Figure 8).

Should the air replenishing port be disposed at a distance 12 greater than (Figure 1), it should be disposed within the zone of movement of the piston 5 along the trajectory S1 (Figure 8) between the points d and c during the time t2. During the time t2 there will be no air escape from the air spring 9 (Figure 1) through such an air replenishing port (see S23 in Figure 8) so that the hammer piston 6 can be raised to a greater height (Figure 1) and will have a higher impact energy.

The greater is the distance 12 (Figure 8), the smaller is the effect of the air replenishing port disposed atthis distance on impact energy.

Therefore, in case where air replenishing ports are spaced axially along the cylinder4 (Figure 1), impact energy cannot be reduced to a desired level, e.g. to zero, and the range of impact energy control is rather narrow.

Further rotation of the knob 20 results in rotation of the sleeve 17 until the port 23 of the sleeve 17 is brought in registry with the air replenishing port 13 (Figure 2), the two preceding air replenishing ports 11 and 12 remaining open. This is achieved owing to different position and configuration of the ports 21, 22, 23, 24 of the sleeve 17 and also by the position of respective elements for selectively uncovering the air replenishing ports 11, 12, 13, 14 of the cylinder 4, which comprise portions 25, 26, 27, 28 of the wall of the sleeve 17.

Uncovering the air replenishing port 13 spaced at the distance! (Figure 1) from the end face 16 of the hammer piston 6 results in an increase in air leakage from the air spring 9 thus bringing about a corresponding decrease in impact energy of the hammer piston 6.

Further rotation of the knob 20 will result in all ports 21 (Figure 2), 22,23, 24 of the sleeve 17 being brought in registry with the air replenishing ports 11,12,13,14 of the cylinder 4. Thus, all air replenishing ports 11, 12, 13, 14 will be open, and this will cause a still greater reduction of impact energy of the hammer piston 6.

Therefore, when the air replenishing ports 11, 12, 13, 14 are disposed in a plane drawn at right angles to the axis of the cylinder 4, the air spring 9 is connected to atmosphere with each next air replenishing port being uncovered for a longer period of time during intervals between two successive blows as compared to known percussive tools of the same type. This results in greater air leakage from the air spring 9 and greater reduction of impact energy of the hammer piston upon successive uncovering of the air replenishing ports 11,12,13,14.

The progressive reduction of impact energy upon uncovering each next air replenishing port 11, 12, 13, may continue up to zero value of impact energy without an increase in the number of the air replenishing ports 11, 12, 13, 14, and the range of control of impact energy of the hammer piston 6 may be enlarged to maximum extent possible (Figure 1).

When the sleeve 17 (Figure 4) is installed in the zone of the air replenishing ports 11,12, 13, 14, in a fixed relationship to the casing 1, the air replenishing ports 11,12,13, 14are uncovered by turning the cylinder 4 with respect to the sleeve 17.

The rotation of the cylinder 4 about its own axis is effected by the knob 20 having its eccentric pin 19 cooperating with the groove 29 of the cylinder 4.

The provision of the air replenishing ports 11 (Figure 5), 12, 13, 14 in one and the same plane drawn at right angles to the axis of the cylinder 4 makes it possible to make the sleeve 17 integral with the casing 1. In this case the tool design is simplified.

The casing 1 has the grooves 30,31,32,33 and the elements for selectively uncovering the air replenishing ports 11,12,13, 14 comprise portions of the wall of the casing 1 between the grooves 30, 31,32,33. Upon turning the cylinder 4 the element for selectively uncovering the air replenishing ports 11, 12, 13, 14will uncover them.

The sleeve 17 (Figure 6) may be installed for axial movement with respect to the cylinder 4. This movement is effected by turning the knob 20 having its eccentric pin 19 cooperating with the annular groove 35.

This movement is accompanied by successive uncovering of the air replenishing ports 11,12, 13, 14 by the bevel cut 36 of the wall of the sleeve 17 or by a row of circumferentially space ports 37 (Figure 7), 38, 39, 40 having their dimensions in the axial direction along the sleeve progressively increasing from one port to another, the ports being disposed in the zone of the air replenishing ports 11, 12, 13, 14 of the cylinder 4.

This construction of the sleeve 17 facilitates manufacture of the tool.

Therefore, the air-spring percussive tool according to the invention enables the control of impact energy of the hammer piston 6 over a wide range without changes in the blow rate. Thus the productivity of demolishing of a workpiece material can be matched with the rate of removal of drillings when working with a hammer drill so as to achieve maximum drilling speed independent of strength of the workpiece material.

Such a hammer drill will be free of working tool jamming problems, whereby reliability of the working tool and rotary drive of the hammer drill is improved.

Claims (7)

1. An air-spring percussive tool, comprising a casing accommodating a drive, a working tool, a cylinder which has air replenishing ports disposed in one and the same plane drawn at right angles to the axis of the cylinder and in which are installed a piston connected to the drive and a hammer piston coupled to the piston by means of an air spring and cooperating with the working tool, a sleeve surrounding the cylinder, mounted for a movement with respect thereto and having an element for selectively uncovering the air replenishing ports of the cylinder when the sleeve is displaced.

2. An air-spring percussive tool as claimed in claim 1, wherein the sleeve is mounted for rotation with respect to the cylinder and the element for selectively uncovering the air replenishing ports comprises a portion of the sleeve wall.

3. An air-spring percussive tool as claimed in claim 1, wherein the sleeve is mounted in a fixed relationship to the casing and the cylinder is mounted for rotation about its own axis, the element for selectively uncovering the air replenishing ports comprising a portion of the sleeve wali.

4. An air-spring percussive tool as claimed in claim 1, wherein the sleeve is made integral with the casing and the element for selectively uncovering the air replenishing ports comprises portions of the casing wall between grooves in the casing wall.

5. An air-spring percussive tool as claimed in claim 1, wherein the sleeve is mounted for axial movement with respect to the cylinder and the element for selectively uncovering the air replenishing ports comprises a bevel cut of the sleeve wall.

6. An air-spring percussive tool as claimed in claim 1, wherein the sleeve is mounted for axial movement along the cylinder and the element for selectively uncovering the air replenishing ports comprises a row of circumferentially spaced ports, dimension of the ports in the axial direction along the sleeve progressively increasing from one port to another.

7. An air-spring percussive tool as claimed in any of the foregoing claims substantially as hereinabove described with reference to, and as shown in the accompanying drawings.