GB2313084A

GB2313084A - Hammer drill with mechanism for preventing useless strikes

Info

Publication number: GB2313084A
Application number: GB9709700A
Authority: GB
Inventors: Kyouji Araki
Original assignee: Ryobi Ltd
Current assignee: Ryobi Ltd
Priority date: 1996-05-15
Filing date: 1997-05-13
Publication date: 1997-11-19
Anticipated expiration: 2017-05-13
Also published as: JP3369844B2; CN1169903A; ITTO970392A0; GB9709700D0; JPH09300241A; GB2313084B; ITTO970392A1; IT1294387B1

Abstract

A hammer drill has a rotatably driven cylinder 2 which drives a tool bit 10 via an adapter 3 which slidably engages with the cylinder by means of a splined region 2G,3G on each of the two bodies. A piston 16 is caused to reciprocate within the cylinder and this causes a striker 9 to reciprocate via an air cushion created in a chamber 41. The striker further causes the tool bit to reciprocate against a work piece. When there is no pressure on the tool against a work piece the adapter is allowed to remain at the forward end of the tool and a resilient member 4 prevents any rearward motion of the adaptor. In this manner no striking action is transmitted to the adaptor to thus prevent the occurrence of useless strikes. As pressure is applied to the workpiece the adaptor is pushed rearwards to overcome the resistance of the resilient member and striking action is enabled.

Description

A power driven Hammer Drill having a Mechanism for pteventing useless strikes Cross-Reference to Related Applications This application is based on Application No.

Hei 8-119907 filed on May 15, 1996 in Japan, the content of which is incorporated hereinto by reference.

BACKGROUND OF INVENTION 1. Field of the Invention The present invention relates to structure of a power driven hammer drill, more specifically, a power driven hammer drill with a mechanism which can reliably prevent useless strikes.

2. Description of the Related Art A conventional power driven hammer drill is shown in Fig. 3. A bit 10 installed in the forward end of the hammer drill is rotated in accordance with a power generated at a motor. Objects to be crushed and to be broken such as the objects made of concrete or the like are crushed and are broken as a result of carrying out hammering action by reciprocating the bit 10 in directions of arrow 90 and arrow 91 in addition to drilling action of the bit 10 when the bit 10 is pressed to the objects (full operation). Thus, the hammer drill shown in Fig. 3 carries out drilling action of the bit 10 solely and does not carry out any hammering action solely until when the bit 10 is pressed to the object (out of full operation).

Mechanisms of the drilling action, the hammering action, and anti-useless-strike (to prevent the hammering action of the bit 10 when the hammer drill is under the out of full operation) of the hammer drill are described hereinbelow. The bit 10 is held in an adapter 3, the adapter 3 is positioned in a cylinder 2. Both the cylinder 2 and the adapter 3 are engaged with each other through a spline part 2G and another spline part 3G. So that, although the adapter 3 can be moved freely in the directions of the arrow 90 and the arrow 91 within the cylinder 2, the adapter 3 can not be rotated independent of the cylinder 2.

A bevel pinion gear 32 connected to a transmitting shaft 30 is engaged with a bevel gears 33 fixed to outer surfaces of the cylinder 2. The transmitting shaft 30 is rotated in accordance with the power generated at the motor, so that cylinder 2 is rotated through rotation of both the bevel pinion gear 32 and the bevel gears 33. The adapter 3 is rotated by rotation of the cylinder 2 since the cylinder 2 and the adapter 3 are engaged with the spline part 2G and another spline part 3G as described in above. As a result, the bit 10 held in the adapter 3 is rotated in response to rotation of the adapter 3.

On the other hand, a striker 9 and a piston 16 are held movably in the directions of arrow 90 and arrow 91 within the cylinder 2. A crank shaft 26 is rotated in accordance with the power generated at the motor, a wobble pin 28 is fixed at a position eccentric to the crank shaft 26. The wobble pin 28 and the piston 16 are connected with each other via a connecting rod 17. So that, the piston 16 is moved reciprocally in the directions of arrow 90 and arrow 91 in accordance with rotation of the crank shaft 26.

Fig. 3 is a sectional side elevation of the hammer drill showing the full operation, in other words showing a condition that both of the adapter 3 and the striker 9 are moved toward the direction of arrow 91 as a result of pressing the bit 10 to the object. In the condition, the striker 9 is moved reciprocally due to air pressure in a first chamber 41 compressed by reciprocating movement of the piston 16. The air pressure in the first chamber 41 is maintained under a certain value by an 0 ring 18 provided to the striker 9 and another 0 ring 19 fixed to the piston 16.

Thereafter, the bit 10 is moved reciprocally in addition to the rotating action as a result of striking the adapter 3 toward the direction of arrow 90 by the striker 9. The air pressure in a second chamber 42 formed forwardly to the striker 9 is always almost equal to the atmosphere because of breathing holes 21 formed through the cylinder 2. Therefore, reciprocating movement of the striker 9 is not disturbed by the air pressure in the second chamber 42.

Useless-strike is prevented in the out of full operation when the bit 10 is detached from the objects by the mechanism described hereunder. The adapter 3 is moved toward the direction of arrow 90 in response to strike by the striker 9 from the condition shown in Fig.

3 when the bit 10 is detached from the objects. Thus, the striker 9 is moved further toward the direction of arrow 90. Although another breathing holes 22 formed through the cylinder 2 are closed with the striker 9 when the hammer drill is used under the full operation, the breathing holes 22 are opened when the striker 9 is moved toward the direction of arrow 90. So that, the air pressure of the first chamber 41 maintained under a certain value is made almost equally to the atmosphere.

Thus, reciprocating movement of the piston 16 is not transmitted to the striker 9 because the first chamber 41 is widen by forward movement of the striker 9 as well as opening of the breathing holes 22 in the first chamber 41. As a result, useless-strike of the bit 10 is prevented when the hammer drill is under the out of full operation. A plurality of steel balls 24 are provided on the inner surface of the cylinder 2. The steel balls thus provided are engaged with a groove 9a formed on the striker 9 in order to fix the position of the striker 9 when the hammer drill is used under the out of full operation.

The striker 9 is moved in the direction of arrow 91 as a result of pressing the bit 10 to the objects when the full operation is carried out again.

The bit 10 is positioned as shown in Fig. 3. Thus, the breathing holes 22 are closed by the striker 9, so that reciprocating movement of the piston 16 is transmitted to the striker 9 through the air compressed in the first chamber 41. The bit 10 carries out hammering action in addition to rotating action by striking the adapter 3 with the striker 9.

However, the conventional hammer drill described in above has following problem to be resolved.

Useless-strike in the out of full operation is prevented by opening the breathing holes 22 formed through the first chamber 41. The first chamber 41 can not be opened sufficiently enough for preventing the useless-strike by the breathing holes 22. In addition, prevention of the useless-strike can not be carried out reliably because strike of the adapter 3 is disturbed indirectly by restricting reciprocating movement of the striker 9.

Another conventional power driven hammer is disclosed in Japanese utility model laid-open publication No. SHO 62-181382. Fig. 4 is a sectional side elevation of the hammer. The hammer only carries out hammering action, and no drilling action is carried out in order to crush the objects to be crushed. In this hammer, a piston 16 held in a cylinder 48 is moved in the directions of arrow 90 and arrow 91 reciprocally. So that, a striker 9 is moved reciprocally due to the air in a first chamber 41 compressed by reciprocating movement of the piston 16. As a result, an adapter 45 is struck by the striker 9.

A groove 46 is formed on the adapter 45. An O ring 47 is provided on an inner surface of the cylinder 48. Rebound (movement in the direction of arrow 91) of the adapter 45 is restricted by engaging the 0 ring 47 into the groove 46 in the out of full operation when the bit 10 is detached from the objects. Thus, uselessstrike is prevented by disturbing the reciprocal period of the adapter 45.

However, the spline part 2G and the spline part 3G shown in Fig. 3 are not formed on both the cylinder 48 and the adapter 45 because no drilling action is carried out by the hammer. So that, the structure of the hammer shown in Fig. 4 can not be applied as it is to the hammer drill shown in Fig. 3. In other words, the 0 ring 47 is worn out by frequent contact with the spline 3G supposing that the 0 ring 47 (Fig. 4) for engaging the adapter 3 is provided to the cylinder 2 shown in Fig. 3 as well as forming a groove on vicinity of rear end of the adapter 3.

Besides, it is possible to employ the structure of providing the 0 ring in a front cover 6 shown in Fig.

3 as well as forming another groove on vicinity of forward end of the adapter 3 (vicinity of 0 rings 23) in order to avoid contact between the 0 rings 47 and the spline part 3G. The 0 ring provided to the front cover 6 is worn out by frequent contact with the adapter 3 because of rotation of the adapter 3 even when the front cover 6 shown in Fig. 3 is not rotated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power driven hammer drill with anti-uselessstrike mechanism capable of preventing useless strike reliably as well as avoiding wear out a contacting member such as 0 ring or the like.

In accordance with characteristic of the present invention, a power driven hammer drill with antiuseless-strike mechanism comprises a cylinder having a cylinder engagement part on an inner surface of the cylinder and being rotated in accordance with a power generated at a power source, and a reciprocating member positioned in the cylinder and having a reciprocating engagement part being engaged with the cylinder engagement part, the reciprocating member being moved reciprocally along with an axis of rotation of the cylinder in accordance with the power generated at the power source with maintaining engagement of the cylinder engagement part and the reciprocating engagement part, the power driven hammer drill including a bit being rotated in accordance with rotation of the cylinder and being moved reciprocally in accordance with reciprocating movement of the reciprocating member, the bit being attachable to the power driven hammer drill, wherein a contact member is provided on either of the inner surface of the cylinder or the reciprocating member, and wherein a part to be contacted is located on either of the inner surface of the cylinder or the reciprocating member mated with the contact member, and wherein the bit is rotated in accordance with rotation of the cylinder, the bit is moved reciprocally by moving the reciprocating member within a range out of contact between the contact member and the part to be contacted when the power driven hammer drill is under the full operation, and wherein the bit is rotated solely in accordance with rotation of the cylinder, the bit is not moved reciprocally by suspending reciprocating movement of the reciprocating member by contacting the contact member with the part to be contacted when the power driven hammer drill is under out of full operation.

While the novel features of the invention are set forth in a general fashion, both as to organization and content, it will be better understood and appreciated, along with other objections and features thereof, from the following detailed description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional side elevation of a power driven hammer drill with anti-useless-strike mechanism of an embodiment of the present invention.

Fig. 2A is an enlarged side elevation of the hammer drill, particularly in vicinity of a cylinder 2, an adapter 3 and a front cover 6 each of which shown in Fig. 1 when the hammer drill is under full operation.

Fig. 2B is an enlarged side elevation of the hammer drill, particularly in vicinity of a cylinder 2, the adapter 3 and the front cover 6 when the hammer drill is under the out of full operation.

Fig. 3 is a sectional side elevation of a conventional power driven hammer drill.

Fig. 4 is a sectional side elevation of a conventional power driven hammer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a power driven hammer drill with anti-useless-strike mechanism in the present invention will be described in accordance with drawings.

Fig. 1 is a sectional side elevation of the hammer drill.

Fig. 2A and Fig. 2B are enlarged side elevations of the hammer drill, particularly in vicinity of a cylinder 2, an adapter 3 and a front cover 6 each of which shown in Fig. 1. Fig. 2A shows a condition when the hammer drill is under the full operation and Fig. 2B is a view showing a condition when the hammer drill is under the out of full operation.

A bit 10 mounted in the forward end of the hammer drill is rotated in accordance with a power generated at a motor 13 as power source. Objects to be crushed and to be broken such as objects made of concrete or the like are crushed and broken as a result of carrying out hammering action by reciprocating the bit 10 in directions of arrow 90 and arrow 91 in addition to drilling action of the bit 10 when the bit 10 is pressed to the objects (full operation).

Thus, the hammer drill in this embodiment carries out only drilling action of the bit 10 and does not carry out any hammering action until when the bit 10 is pressed to the objects (full operation). Overall structure, operation in both full and out of full operation of the hammer drill are described hereinbelow.

[Overall Structure] The bit 10 is installed in the adapter 3 as reciprocating member positioned at the forward end of the cylinder 2. A spline part 2G as cylinder engagement part is formed on an inner surface of the cylinder 2, and another spline part 3G as reciprocating engagement part is formed on an outer surface of the adapter 3.

Both of the spline part 2G of the cylinder 2 and the spline part 3G of the adapter 3 are formed in tooth (groove) shape along the rotation axis L1 of the cylinder 2. Both of the spline parts are formed so as to engaged and coupled with each other. Thus, the adapter 3 can be moved reciprocally along with the rotation axis by sliding. In the same time, rotation of the cylinder 2 is transmitted to the adapter 3. In other words, a spline shaft is composed by both the cylinder 2 and the adapter 3.

The cylinder 2 is held rotatably in the a barrel 7 via a bearing 8. The bit 10 is installed in a direction so as to be identical with the rotation axis L1 of the cylinder 2. Further, the adapter 3 is moved reciprocally along the rotation axis L1 (both the directions of arrow 90 and arrow 91).

The front cover 6 is fixed at the forward end of the barrel 7. A plurality of 0 rings 23 are provided to a surface of the adapter 3 formed opposite to the front cover 6 in order to prevent leakage of lubricant toward the forward end of the front cover 6. A bevel gear 33 is fixed to vicinity of the rear end of the cylinder 2. A bevel pinion gear 32 connected to a transmitting shaft 30 is engaged with the bevel gear 33.

Also, a transmitting shaft gear 31 is fixed to the transmitting shaft 30.

A motor 13 starts its operation as a result of turning on the switching part 15 when a trigger 14 of a handle 34 shown in Fig. 1 is gripped deeply. On the other hand, the motor 13 is under the out of operation as a result of turning off the switching part 15 when the trigger 14 is released and recovered to the original position. A pinion gear 25 is formed on the motor shaft connected to the motor 13. Also, a crank shaft 26 is held rotatably in the body of the hammer drill, and the pinion gear 25 of the motor shaft is engaged with a crank shaft gear 27 fixed to the crank shaft 26.

The transmitting shaft gear 31 is also engaged with the crank shaft gear 27 of the crank shaft 26. So that, rotation generated at the motor 13 is transmitted to the transmitting shaft 30 via the crank shaft 26. The rotation is then transmitted to the cylinder 2 via the bevel pinion gear 32 of the transmitting shaft 30 and bevel gear 33 of the cylinder 2, both of the bevel gears are engaged with each other. Thus, the cylinder 2 is rotated by the rotation generated at the motor 13.

On the other hand, both of a striker 9 and a piston 16 are held movably in the cylinder 2 toward the directions of arrow 90 and arrow 91. One end of a connecting rod 17 is connected to the piston 16. Also, a wobble pin 28 is provided eccentric from the center of the crank shaft 26. The other end of the connecting rod 17 is connected to the wobble pin 28. Rotation of the crank shaft 26 is converted into reciprocating movement toward the directions of arrow 90 and arrow 91 by the wobble pin 28 and the connecting rod 17.

[Full operation] Details of the full operation of the hammer drill in this embodiment is described herein. The objects to be crushed and be broken such as concrete or the like are crushed and broken by means of carrying out drilling and hammering action of the bit 10 as a result of pressing the bit 10 to the objects when the hammer drill is under the full operation as described in above.

Both of Fig. 1 and Fig. 2A show conditions of the hammer drill when the hammer drill is under the full operation.

The striker 9 and other parts are not shown in Fig 2A.

As described in above, rotation generated at the motor 13 is transmitted to the transmitting shaft 30 via the crank shaft 26. Then the rotation is finally transmitted to the cylinder 2 by the engagement of the bevel pinion gear 32 of the transmitting shaft 30 and the bevel gear 33 of the cylinder 2. Thus, the bit 10 is rotated as a result of rotation of the adapter 3 engaged with the cylinder 2 by means of spline connection because the cylinder 2 is rotated.

Besides, rotation of the crank shaft 26 is transmitted to the piston 16 as reciprocating movement toward the directions of arrow 90 and arrow 91 via the wobble pin 28 and the connecting rod 17. The striker 9 is moved reciprocally as a result of variation of the air pressure in a first chamber 41 formed between piston 16 and the striker 9 when the piston 16 is moved reciprocally.

Then, the adapter 3 is struck by the striker 9 in the direction of arrow 90, so that the bit 10 carries out hammering action. The air pressure in the first chamber 41 is maintained in a certain value by means of an 0 ring 18 provided to the striker 9 and another 0 ring 19 provided in the piston 16. Also, an adjusting hole 29 is formed in the cylinder 2. The adjusting hole 29 is utilized for adjusting the air pressure in the first chamber 41. So that, the striker 9 is moved reciprocally with efficiency.

As described in above, the bit 10 carries out both drilling and hammering action when the hammer drill is under the full operation as described in above.

Breathing holes 22 are formed in the cylinder 2 as shown in Fig 1. The breathing holes 22 are covered with the striker 9 since the striker 9 is pushed toward the direction of arrow 91 by the bit 10 and the adapter 3 when the hammer drill is under the full operation.

Further, a second chamber 42 formed at the forward end of the striker 9 is always opened by breathing holes 21 formed in the cylinder 2. Therefore, reciprocating movement of the striker 9 is not disturbed by the air pressure in the second chamber 42.

tOut of full operation] Both of the striker 9 and the adapter 3 are moved toward the direction of arrow 90 from the condition shown in Fig. 1 in the out of full operation when the bit 10 is detached from the objects.

Fig. 2B is an enlarged side elevation of the hammer drill, particularly in vicinity of a cylinder 2, the adapter 3 and the front cover 6 when the hammer drill is under the out of full operation. The striker 9 is not shown in Fig. 2B.

As shown in Fig. 2B, a cut-out groove is formed in the forward end of the cylinder 2. An 0 ring 4 for contact as contact member is provided in the groove. The 0 ring 4 having sufficient elasticity is compressed with the adapter 3 when the hammer drill is under the full operation as shown in Fig. 2A.

A circular cone 5 as part to be contacted is formed on the outer surface of the adapter 3. The spline part 3G is provided to a lower part of the step. The circular cone 5 contacts with a circular cone inner surface 2M formed in the inner surface of the cylinder 2.

So that, movement of the adapter 3 toward the direction of arrow 91 is restricted when the hammer drill is under the full operation (see Fig. 2A). In this embodiment, the circular cone 5 is equivalent to reciprocating member circular cone, and the circular cone inner surface 2M is equivalent to cylinder circular cone.

The 0 ring 4 for contact is positioned on the lower part of the step in the out of full operation when the adapter 3 is moved toward the direction of arrow 90.

In that case, both the 0 ring 4 for contact and the spline part 3G are not contacted with each other. Thus, the 0 ring 4 for contact is never be worn out by contacting with the spline 3G.

The shape of the 0 ring 4 for contact is recovered to the original shape as a result of releasing the compression due to the elasticity when the 0 ring 4 for contact is positioned on the lower part of the step.

Thus, movement of the adapter 3 toward the direction of arrow 91 is restricted by contacting the 0 ring 4 for contact with the circular cone 5 of the adapter 3. So that, it is possible to prevent useless-strike of the hammer drill reliably, because no hammering action is carried out by the adapter 3 and the bit 10 when the hammer drill is under the out of full operation.

As described in above, the circular cone 5 is formed for restricting the movement of the adapter 3 toward the direction of arrow 91 by contacting with the circular cone inner surface 2M of the cylinder 2 when the hammer drill is under the full operation. It is not necessary to form additional part to be contacted since the circular cone 5 is utilized as the part to be contacted in the embodiment descried in above.

The striker 9 is moved toward the direction of arrow 90 shown in Fig. 1 when the hammer drill is under the out of full operation. So that, the breathing holes 22 formed in the cylinder 2 are lead into the first chamber 41 as a result of widening the first chamber 41.

Thus, reciprocating movement of the piston 16 is not transmitted to the striker 9, so that the striker 9 is not moved reciprocally toward the directions of arrow 90 and arrow 91.

Further, a plurality of steel balls 24 are provided on the inner surface of the cylinder 2 as shown in Fig. 1. Movement of the striker 9 is restricted by contacting the steel balls 24 with grooves 9a formed on the striker 9. The steel balls 24 are pushed inwardly by an 0 ring positioned at outer side of the steel balls 24.

Thus, movement of the striker 9 toward the directions of arrow 90 and arrow 91 is restricted when the hammer drill is under the out of full operation in addition to restricting movement of the adapter 3 toward the directions of arrow 90 and arrow 91. Therefore, it is possible to prevent useless-strike more reliably.

As described in above, movement of the adapter 3 holding the bit 10 is restricted directly by contacting the 0 ring 4 for contact with the circular cone 5 of the adapter 3 when the hammer drill is under the out of full operation. So that, it is possible to prevent uselessstrike of the hammer drill reliably. The bit 10 carries out drilling action solely because the cylinder 2 is rotated in accordance with the power generated at the motor 13 even when the hammer drill is under the out of full operation.

The bit 10 is pressed to the objects to be crushed and be broken when the full operation is carried out again. The adapter 3 is moved toward the direction of arrow 91 by the pushing force. So that, the 0 ring 4 for contact is compressed along the surface of the circular cone 5 as shown in Fig. 2A. Further, reciprocating movement of the piston 16 is transmitted to the striker 9 as a result of covering the breathing holes 22 with the striker 9 moved toward the direction of arrow 91. Thus, the bit 10 carries out hammering action in addition to rotating action.

The adapter 3 is moved reciprocally within a range that both the 0 ring 4 for contact and the circular cone 5 do not contact with each other when the hammer drill is under the full operation shown in Fig. 1 and Fig. 2A. Thus, hammering action carried out by the bit 10 is not disturbed with both of the 0 ring 4 for contact and the circular cone 5.

[Other embodiment] Although the 0 ring 4 as the contact member is provided to the cylinder 2 and the circular cone 5 as the part to be contacted is formed on the adapter 3 in the embodiment described in above, it is possible to provide the contact member to the adapter 3 as well as forming the part to be contacted to the cylinder 2.

Further, though the cylinder 2 and the adapter 3 are used as the cylinder and the reciprocating member respectively as an instance in the embodiment described in above, other objects having different shapes or structures can be employed. Also, the 0 ring 4 for contact and the circular cone 5 are used as the contact member and the part to be contacted respectively as an instance in the embodiment described in above. The contact member and the part to be contacted in the present invention are not limited to the 0 ring 4 for contact and the circular cone 5. In other words, other objects having different shapes or structures can be employed as the contact member and the part to be contacted as long as both of the contact member and the part to be contacted make no contact with each other in the full operation, and make contact with each other in the out of full operation in order to suspend the reciprocating movement of the reciprocating member.

Further, the bit 10 is held directly with the adapter 3 in the embodiment described in above. The bit 10 can be held with other parts instead of the adapter 3 as long as the bit 10 is rotated in accordance with rotation of the cylinder and is moved reciprocally in response to reciprocating movement of the reciprocating member.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

[Advantages of the present invention] In the power driven hammer drill with antiuseless-strike mechanism of the present invention, the contact member is provided on either of the inner surface of the cylinder or the reciprocating member, and the part to be contacted is located on either of the inner surface of the cylinder or the reciprocating member mated with the contact member.

The bit is rotated in accordance with rotation of the cylinder, the bit is moved reciprocally by moving the reciprocating member within a range out of contact between the contact member and the part to be contacted when the power driven hammer drill is under the full operation. Also, the bit is rotated solely in accordance with rotation of the cylinder, the bit is not moved reciprocally by suspending reciprocating movement of the reciprocating member by contacting the contact member with the part to be contacted when the power driven hammer drill is under the out of full operation.

Thus, reciprocating movement of the bit in the out of full operation (useless-strike) can be prevented reliably by contacting the contact member with the part to be contacted.

Further, reciprocating movement of the reciprocating member is not disturbed by the contact member because the reciprocating member is moved reciprocally within a range out of contact between the contact member and the part to be contacted when the power driven hammer drill is under the full operation.

Thus, both of rotation and reciprocating movement of the bit can be carried out reliably when the hammer drill is under the full operation.

Still further, in the power driven hammer drill with anti-useless-strike mechanism of the present invention, the contact member is located in a position out of contact to both the cylinder engagement part and the reciprocating engagement part. Therefore, the contact member is never be worn out by contacting with either of the cylinder engagement part or the reciprocating engagement part.

Claims

What is claimed is:

1. A power driven hammer drill with antiuseless-strike mechanism comprising a cylinder having a cylinder engagement part on an inner surface of the cylinder and being rotated in accordance with a power generated at a power source, and a reciprocating member positioned in the cylinder and having a reciprocating engagement part being engaged with the cylinder engagement part, the reciprocating member being moved reciprocally along with an axis of rotation of the cylinder in accordance with the power generated at the power source with maintaining engagement of the cylinder engagement part and the reciprocating engagement part, the power driven hammer drill including a bit being rotated in accordance with rotation of the cylinder and being moved reciprocally in accordance with reciprocating movement of the reciprocating member, the bit being attachable to the power driven hammer drill, wherein a contact member is provided on either of the inner surface of the cylinder or the reciprocating member, and wherein a part to be contacted is located on either of the inner surface of the cylinder or the reciprocating member mated with the contact member, and wherein the bit is rotated in accordance with rotation of the cylinder, the bit is moved reciprocally by moving the reciprocating member within a range out of contact between the contact member and the part to be contacted when the power driven hammer drill is under full operation, and wherein the bit is rotated solely in accordance with rotation of the cylinder, the bit is not moved reciprocally by suspending reciprocating movement of the reciprocating member by contacting the contact member with the part to be contacted when the power driven hammer drill is under out of full operation.

2. A power driven hammer drill with antiuseless-strike mechanism in accordance with claim 1, wherein the contact member is located in a position out of contact to both the cylinder engagement part and the reciprocating engagement part.

3. A power driven hammer drill with antiuseless-strike mechanism in accordance with claim 2, wherein a cylinder circular cone is formed on the inner surface of the cylinder, and wherein a reciprocating member circular cone capable of being contacted to the cylinder circular cone is located on an outer surface of the reciprocating member, and wherein reciprocating movement of the reciprocating member is suspended by contacting either of the cylinder circular cone or the reciprocating member circular cone both of which equivalent to the part to be contacted with the contact member when the power driven hammer drill is under the out of full operation.

4. A power driven hammer drill with antiuseless-strike mechanism comprising a cylinder having a cylinder engagement part on an inner surface of the cylinder and being rotated in accordance with a power generated at a power source, and a reciprocating member positioned in the cylinder and having a reciprocating engagement part being engaged with the cylinder engagement part, the reciprocating member being moved reciprocally along with an axis of rotation of the cylinder in accordance with the power generated at the power source with maintaining engagement of the cylinder engagement part and the reciprocating engagement part, the power driven hammer drill including a bit being rotated in accordance with rotation of the cylinder and being moved reciprocally in accordance with reciprocating movement of the reciprocating member, the bit being attachable to the power driven hammer drill, wherein a contact member having elasticity is provided on the inner surface of the cylinder, and wherein a reciprocating member circular cone is located on an outer surface of the reciprocating member, and wherein the bit is rotated in accordance with rotation of the cylinder, the bit is moved reciprocally by moving the reciprocating member within a range out of contact between the reciprocating member circular cone and the contact member by applying a pressure to the contact member with outer surfaces of the reciprocating member except for the reciprocating member circular cone when the power driven hammer drill is under the full operation, and wherein the bit is rotated solely in accordance with rotation of the cylinder, the bit is not moved reciprocally by suspending reciprocating movement of the reciprocating member by contacting the contact member with the reciprocating member circular cone when the power driven hammer drill is under the out of full operation.

5. A power driven hammer drill having a mechanism for preventing useless strikes comprising: a cylinder having a cylinder engagement part on an inner surface of the cylinder and being rotated in accordance with a power generated at a power source, and a reciprocating member positioned in the cylinder and having a reciprocating engagement part engaged with the cylinder engagement part, the reciprocating member being movable reciprocally along an axis of rotation of the cylinder in accordance with the power generated at the power source while maintaining engagement of the cylinder engagement part and the reciprocating engagement part, wherein a first contact member is provided on either the inner surface of the cylinder or the reciprocating member, and a second contact member is located on either the inner surface of the cylinder or the reciprocating member such that when the drill is under full operation the cylinder is rotated and the reciprocating member moved reciprocally, the first contact member and second contact member making no contact with each other and when the drill is not under full operation the cylinder is rotated but the movement of the reciprocating member is suspended by contact of the first contact member with the second contact member.

6. A power driven hammer drill substantially as herein described with reference to figures 1 and 2 of the accompanying drawings.