Patent Publication Number: US-7213659-B2

Title: Impact drill

Description:
BACKGROUND OF THE INVENTION 
   1. Filed of the Invention 
   The present invention relates to an impact drill for use in a drilling operation on the concrete, mortar or tile, for example, and more particularly to an impact drill having a drill mode for performing a drilling operation by rotating a drill bit and an impact drill mode for performing a drilling operation by rotating and vibrating the drill bit. 
   2. Description of the Related Art 
     FIG. 1  shows a conventional example of the impact drill of this kind. In  FIG. 1 , reference numeral  1  denotes a main frame portion that forms an outer shell of the impact drill and has the self-contained parts at predetermined positions, including a gear cover  17 , an inner cover  18 , an outer cover  19 , a housing  7  and a handle portion  6 . Reference numeral  2  denotes a spindle inserted transversely through the gear cover  17 , and  3  denotes a drill chuck attached at the top end of the spindle. A rotational ratchet  4  is mounted near the central part of the spindle  2 . The rotational ratchet  4  is rotated along with the rotation of the spindle  2 , and moved along with the axial movement of the spindle  2 . The serrated irregularities are formed on one face  4   a  of the rotational ratchet  4 . 
   Reference numeral  5  denotes a stationary ratchet disposed at a position opposed to the rotational ratchet  4 , in which the serrated irregularities are formed on one face  5   a  of the stationary ratchet. The stationary ratchet  5  has a hollow cylindrical shape, and is fixed to the inner cover  18 , irrespective of the rotation and axial movement of the spindle  2 . 
   On the other hand, a motor  8  is disposed inside the housing  7  linked to the handle portion  6 . A rotational driving force of the motor  8  is transmitted via a gear  10  fixed to a rotation shaft  9  to a second pinion  11 . The second pinion  11  has two pinion portions  11   a ,  11   b  having a different number of teeth, which are engaged with a low speed gear  12  and a high speed gear  13 , respectively. When the second pinion  11  is rotated, both the gears  12 ,  13  are also rotated. 
   Reference numeral  14  denotes a clutch disk engaged with the spindle  2  and mounted to be slidable in the axial direction. If the clutch disk  14  is inserted into a concave portion of the low speed gear  12 , the rotation of the second pinion  11  is transmitted via the low speed gear  12  and the clutch disk  14  to the spindle  2 , as shown in  FIG. 1 . On the other hand, if the clutch disk  14  is slid to the right from the position of  FIG. 1 , and inserted into a concave portion of the high speed gear  13 , the rotation of the second pinion  11  is transmitted via the high speed gear  13  and the clutch disk  14  to the spindle  2 . Accordingly, the spindle  2  can be rotated at low speed or high speed by movement of the clutch disk  14 . 
   Reference numeral  15  denotes a change lever for changing the operation mode of the impact drill, namely, between a drill mode and an impact drill mode. A change shaft  16  is press fit into the change lever  15 , whereby when the change lever  15  is rotated, the change shaft  16  is also rotated. The change shaft  16  has a notch portion  16   a , as shown in  FIGS. 2 ,  3  and  4 , whereby when the notch portion  16   a  is at the position of  FIG. 2 , the impact drill is operated in the drill mode, while when the notch portion  16   a is at the position of  FIG. 3 , the impact drill is operated in the impact drill mode. 
   (A) Drill Mode 
   When a drill bit (not shown) attached in the drill chuck  3  is contacted with a machined surface and the handle portion  6  is pressed in a direction of the arrow in  FIG. 1 , an end part of the spindle  2  makes contact with the change shaft  16  to be immovable to the right, when the notch portion  16   a  of the change shaft  16  is at the position of  FIG. 2 . Accordingly, there is no contact between the irregular face  4   a  of the rotational ratchet  4  and the irregular face  5   a  of the stationary ratchet  5 . Accordingly, a rotational driving force of the motor  8  is transmitted via the low speed gear  12  or high speed gear  13  to the spindle, so that the drill bit is given a rotational force. 
   (B) Impact Drill Mode 
   In an impact drill mode, the notch portion  16   a  of the change shaft  16  is brought into the position of  FIG. 3  by rotating the change lever  15 . Then, the drill bit attached in the drill chuck  3  is contacted with a machined surface. If the handle portion  6  is pushed in a direction of the arrow in  FIG. 1 , an end part of the spindle  2  enters the notch portion  16   a , as shown in  FIG. 4 . That is, the spindle  2  is slightly moved to the right, so that the, irregular face  4   a  of the rotational ratchet  4  is contacted with the irregular face of the stationary ratchet  5 . 
   In drilling the machined surface, if the spindle  2  is rotated in the state of  FIG. 4 , the rotational ratchet  4  is meshed and engaged with the stationary ratchet  5 , and rotated to cause vibration due to the irregular faces of both the ratchets  4  and  5 . This vibration is transmitted through the spindle  2  to the drill bit (not shown). That is, the drill bit is given a rotational force and vibration to perform a drilling operation. 
   However, when the impact drill described above is operated in the impact drill mode, the vibration caused by rotation of the spindle in the state where the irregular faces of the ratchets  4  and  5  are contacted under pressure is transmitted not only to the drill bit, but also through the stationary ratchet  5  and the inner cover  18  from the housing  7  to the handle portion  6 . Therefore, there is a problem that the user of the impact drill undergoes a great vibration, and feels uncomfortable. Especially when the impact drill is continuously employed for a long time, care must be taken not to transmit the vibration to the user and cause adverse effect on the health of the user. 
   Several proposals for reducing the vibration transmitted to the user have been made. For example, in JP-B-2-30169, a structure was disclosed in which a clutch cam  22  is supported movably in the axial direction of the spindle  20 , and biased and urged to a rotary cam  21  by a spring  23 , as shown in  FIG. 5 . 
   In  FIG. 5 , reference numeral  21  denotes a rotary cam that is rotated along with the spindle  20 . A cam face  21   a  of the rotary cam  21  is formed with serrated irregularities. On the other hand, the clutch cam  22  is composed of a hollow cylindrical portion slidable in the axial direction of the spindle  20  and a flange portion  22   b . A cam face  22   c  of the flange portion  22   b  is formed with serrated irregularities. 
   The spring  23  is provided between the flange  22   b  of the clutch cam  22  and a plate  24   a  engaging a groove  22   a  of the clutch cam  22 , and always urges the clutch cam  22  toward the rotary cam  21 . Thus, when the spindle  20  is moved backward, the cam faces  21   a  and  22   c  are contacted under pressure. If a pressing force applied to the spindle  20  overcomes a resilience of the spring  23 , the spring  23  is compressed, so that the clutch cam  22  is moved backward (to the right in the figure). 
   When the clutch cam  22  is moved forward from the back position due to a resilient force of the spring  23 , it collides with the rotary cam  21 , so that the rotary cam  21  is vibrated together with the spindle  20 . With this structure, since the vibration caused by contact between the cam faces  21   a  and  22   c  is relieved by the spring  23  and transmitted to the handle portion (not shown), there is the effect that the vibration transmitted to the user is reduced as compared with the structure in which the ratchet  5  is firmly disposed as shown in  FIG. 1 . 
   In a case of the drill as disclosed in JP-B-2-30169, since the clutch cam  22  permits the spindle  20  to slide in the axial direction, and regulates the rotation, the slide faces  22   e ,  22   e  are vertically formed on both sides of the flange portion  22   b , and the clutch cam  22  is carried between both the guide faces  26  of a retainer  24  extending from the plate  24   a , as shown in  FIG. 6 . 
   When this structure has additionally a function of rotating the spindle  20  at high speed and low speed in the same manner as in  FIG. 1 , it has been found that there occurs a phenomenon that the impact force of the clutch cam  22  in colliding with the rotary cam  21  due to a restoring force of the spring  23  from the back position is weakened, as will be described later. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to solve the above-mentioned problems associated with the prior art, and to provide an impact drill can reduce the vibration transmitted to the user without losing a drilling ability at high and low speed rotation. 
   According one aspect of the invention, there is provided with an impact drill including: a spindle rotated by a motor and movable in an axial direction; a drill chuck fixed to the spindle and mountable with a drill bit; a first ratchet fixed to the spindle and having a face including an irregular portion; a second ratchet having a face including an irregular portion opposed to the face of the irregular portion of the first ratchet and movable in the axial direction, and a spring for urging the second ratchet in a direction of the first ratchet, in which the spindle is given an axial vibration by a contact and separation action between the irregular faces of the first and second ratchets due to a relative rotation of the first ratchet to the second ratchet, wherein the second ratchet is supported to be rotatable within a predetermined range in a rotational direction thereof. 
   According to another aspect of the invention, the second ratchet is supported to be rotatable by an angle or more from a first position at which the irregular face of the second ratchet overrides the irregular face of the first ratchet to a second position at which the irregular face of the second ratchet engages the irregular face of the first ratchet, when the first ratchet is in a stopped state. 
   According to another aspect of the invention, the second ratchet is supported to be rotatable by 0.6 times an angle or more from a first position at which the irregular face of the second ratchet overrides the irregular face of the first ratchet to a second position at which the irregular face of the second ratchet engages the irregular face of the first ratchet, when the first ratchet is in a stopped state. 
   According to another aspect of the invention, the second ratchet is supported to be rotatable by 0.3 times an angle or more from a first position at which the irregular face of the second ratchet overrides the irregular face of the first ratchet to a second position at which the irregular face of the second ratchet engages the irregular face of the first ratchet most deeply, when the first ratchet is in a stopped state. 
   According to another aspect of the invention, a notch portion is provided on an outer circumference of the second ratchet. A projection portion provided in a main frame portion of the impact drill is inserted into the notch portion. A predetermined clearance is provided between the notch portion and the projection portion. 
   According to another aspect of the invention, a width across flat of two parallel faces is provided in a part on a cylindrical portion of the second ratchet. A notch portion opposed to the width across flat is provided on a main frame portion of the impact drill. A predetermined clearance is provided between the width across flat and the notch portion. 
   According to another aspect of the invention, a projection portion is provided on an outer circumference of the second ratchet. The projection portion is inserted into a notch portion provided in a main frame portion of the impact drill. A predetermined clearance is provided between the projection portion and the notch portion. 
   According to another aspect of the invention, an elastic body is disposed in the predetermined clearance. A thrust bearing is provided between the second ratchet and the spring, or/and between the spring and a side wall portion extending from the main frame portion. 
   It is possible to produce a sufficient impact force between the second ratchet and the first ratchet at high and low speed rotation, whereby an impact drill having excellent drilling ability and unlikely to transmit vibration to the main body is provided. Accordingly, the user of the impact drill does not feel uncomfortable, and injure one&#39;s health. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view showing one example of the conventional impact drill; 
       FIG. 2  is an explanatory view of the impact drill in a drill mode; 
       FIG. 3  is an explanatory view of the impact drill in an impact drill mode; 
       FIG. 4  is an explanatory view of the impact drill in the impact drill mode; 
       FIG. 5  is a partial constitutional view showing another example of the conventional impact drill; 
       FIG. 6  is a partial constitutional view showing another example of the conventional impact drill; 
       FIGS. 7A–7G  are an explanatory view showing how cam collision occurs at high and low speed rotation in another example of the conventional impact drill; 
       FIG. 8  is a cross-sectional view showing an impact drill according to a first embodiment of the invention; 
       FIGS. 9A–9G  are explanatory views showing how cam collision occurs at high and low speed rotations in the impact drill according to the first embodiment of the invention; 
       FIG. 10  is a partial constitutional view showing an impact drill according to a second embodiment of the invention; 
       FIG. 11  is a partial constitutional view showing an impact drill according to a third embodiment of the invention; 
       FIG. 12  is a partial constitutional view showing an impact drill according to a fourth embodiment of the invention; and 
       FIG. 13  is a partial constitutional view showing an impact drill according to a fifth embodiment of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before explaining the embodiments of the invention, there will be described a phenomenon in which when the clutch cam collides with the rotary cam, its impact force is weakened. 
     FIGS. 7A–7G  show a situation where the clutch cam  22  and the rotary cam  21  collide when the spindle  20  is rotated at high speed and low speed in  FIGS. 5 and 6 . Generally, since it is common that the low speed rotation is set at roughly half a number of rotations of the high speed rotation, it is assumed in the following explanation that the rotational motion distance of the rotary cam is 2 h at the high speed rotation and h at the low speed rotation in the time histories  FIGS. 7A to 7G  as represented in the development views of two dimensional plane as shown in  FIGS. 7A–7G . 
   First of all, in the case of high speed rotation, if the rotary cam  21  is rotated (leftward in the figure) in the state as shown in  FIG. 7A , the clutch cam  22  opposed to and contact with the rotary cam  21  is moved backward (upward in the figure) due to inclination of serrated irregularities  21   a  to turn in the state of  FIG. 7B . The arrow  30  of  FIGS. 7A–7G  indicates the rotational direction (left and right direction in the figure) of the rotary cam  21  and the arrow  31  indicates the movement direction (vertical direction in the figure) of the clutch cam  22 . 
   At the stage of  FIG. 7B , the clutch cam  22  is released and separated from the rotary cam  21 , but because the clutch cam  22  is always urged toward the rotary cam  21  by the spring  23  ( FIG. 6 ), the clutch cam  22  begins to move forward (downward in the figure) to the rotary cam  21  in turn, as shown in  FIG. 7C . As a result, the clutch cam  22  and the rotary cam  21  collide, as shown in  FIG. 7D . Thereafter, as the rotary cam  21  is rotated again, the clutch cam  22  repeatedly moves backward and forward as in  FIGS. 7E ,  7 F and  7 G, so that the clutch cam  22  and the rotary cam  21  repeatedly collide on every tooth. 
   If a front surface  22   f  of the clutch cam  22  and a front surface  21   f  of the rotary cam  21  collide as shown in  FIG. 7D , an elastic energy of the spring  23  stored by a backward movement of the clutch cam  22  is transmitted to the rotary cam  22  without loss, causing a great impact force. 
   Next, a collision situation will be described below where under the conditions that the number of rotations of the rotary cam  21 , the weight of the clutch cam  22  and the spring constant of the spring  23  are set up to give rise to the above phenomenon at the time of high speed rotation, the low speed rotation of about half the number of rotations is made. 
   First of all, if the rotary cam  21  is rotated in the state of  FIG. 7A , the clutch cam  22  is moved backward to turn in the state of  FIG. 75 , and further the clutch cam  22  and the rotary cam  21  are separated away, as shown in  FIG. 7C . Thereafter, the clutch cam  22  moves forward to the rotary cam  21  in the same manner as previously described, but because the advancement of the rotary cam  21  is slow, the clutch cam  22  and the rotary cam  21  collide on the back sides  22   g  and  21   g  as shown in FIG.  7 D. At this time of collision, almost half an elastic energy of the spring  23  is consumed to cause a small impact force. 
   Then, at the stage of  FIG. 7E , the back sides are contacted, or the back tooth flanks are repeatedly separated and contacted, so that the clutch cam  22  moves forward. Then, at the stage of  FIG. 7F , the front side  22   f  of the clutch cam  22  and the front side  21   f  of the rotary cam  21  collide. In the collision at this stage, a residual energy from the elastic energy of the spring  23  which has been consumed at the previous stage  FIG. 7D  is employed, and the impact force of collision is small due to a loss caused by contact between the back sides. Thereafter, the clutch cam  22  is moved backward again as shown in  FIG. 7G . 
   As described above, if the settings are made such that one great impact force is generated at high speed rotation, two or more small impact forces are generated at low speed rotation, degrading the drilling ability of the drill. 
   Embodiments of the invention, has been achieved to solve the above-mentioned problems, and will be described below in detail by way of example. 
   First Embodiment 
     FIG. 8  is a constitutional view showing the essence of an impact drill according to a first embodiment of the invention. 
   As shown in  FIG. 8 , a spindle  102  is provided in a main frame portion  101  and moved forward (to the left in the figure) or backward (to the right in the figure) relative to a workpiece  119 . A chuck  103  for mounting a drill bit  118  is provided at the top end of the spindle  102 . A first ratchet  104  and a second ratchet  105  are provided in the almost central part of the main frame portion  101 . The first ratchet  104  is rotated along with the spindle  102  and roved axially, and has serrated irregularities  104   a  on one face. The second ratchet  105  is formed with serrated irregularities  105   d  on a bottom portion  105   c . Also, the second ratchet  105  has a dual cylindrical shape, in which an inner cylindrical portion  105   a  slides on the spindle  102  and an outer cylindrical portion  105   b  slides in the axial direction of the spindle  102  along an inner wall of the rain frame portion  101 . 
   The second ratchet  105  has a notch portion  105   e  in a part of the outer cylindrical portion  105   b , and the main frame portion  101  is provided with a projection  101   a , whereby the projection  101   a  is inserted into the notch portion  105   e . As a result, the rotational notion of the second ratchet  105  is blocked. This embodiment has a feature that there is a clearance  130   a  between the notch portion  105   e  and the projection  101   a , so that the second ratchet  105  can be rotated within a predetermined range. 
   A side wall portion  122  extends in a direction of the spindle inside the rain frame portion  101 , and a spring  120  is provided between the side wall portion  122  and the cylindrical bottom portion  105   c . Reference numeral  109  denotes a rotation shaft to which a rotational driving force is transmitted from a motor (not shown), in which its rotational driving force is transmitted via a gear  110  to a second pinion  111 . Reference numeral  112  denotes a low speed gear,  113  denotes a high speed gear, and  114  denotes a clutch disk, in which when the clutch disk  114  is at the position as shown, a rotational force is transmitted via the low speed gear  112  to the spindle  102 . 
   On the other hand, if the clutch disk  114  is rotated to the position where the high speed gear and the spindle  102  are engaged by rotating a change lever  117 , a rotational force of the second pinion  111  is transmitted via the high speed gear  113  to the spindle  102 . Accordingly, the spindle  102  can be rotated at low speed or high speed depending on the rotated position of the change lever  117 . The experiment of the present inventor has revealed that the vibration transmitted to a hand in the drilling operation is reduced owing to the above constitution. 
     FIGS. 9A–9G  show how the first ratchet  104  and the second ratchet  105  collide when the spindle  102  is rotated at high speed and low speed in the above constitution. The low speed rotation is set at half the number of rotations of the high speed rotation, and the rotational motion distance of the first ratchet  104  is 2 h at high speed rotation and h at low speed rotation in the time histories  FIG. 9A  to  FIG. 9G  represented in the development views of two dimensional plane as shown in  FIGS. 9A–9G . 
   First of all, in the case of high speed rotation, if the first ratchet  104  is rotated (leftward in the figure) in the state as shown in  FIG. 9A , the second ratchet  105  opposed to and contact with the first ratchet  104  is moved backward (upward in the  FIGS. 9A–9G ) due to inclination of serrated irregularities  104   a  to turn in the state of  FIG. 9B . 
   As shown in  FIG. 9B  and  FIG. 9C , the second ratchet  105  is released and separated from the first ratchet  104 , but because the second ratchet  105  is always urged toward the first ratchet  104  by the spring  120  ( FIG. 8 ), the second ratchet  105  moves forward to the first ratchet  104  from the state of  FIG. 9C  As a result, the second ratchet  105  and the first ratchet  104  collide, as shown in  FIG. 9D . Thereafter, the second ratchet  105  repeatedly moves backward and forward as in  FIG. 9E ,  FIG. 9F  and  FIG. 9G , so that the second ratchet  105  and the first ratchet  104  repeatedly collide. 
   At the stage of  FIG. 9D , the collision faces between the second ratchet  105  and the first ratchet  104  are always the front sides  105   f  and  104   f , thereby allowing an elastic energy of the spring  120  ( FIG. 8 ) to be transmitted to the first ratchet  104  without loss at every time and causing a great impact force. 
   A collision situation will be described below where under the conditions that the number of rotations of the first ratchet  104 , the weight of the second ratchet  105  and the spring constant of the spring  120  ( FIG. 8 ) are set up to give rise to the phenomenon at the time of high speed rotation, the low speed rotation of about half the number of rotations is made. 
   At low speed rotation, as the first ratchet  104  is rotated, as shown in  FIGS. 9A and 9B , the second ratchet  105  is raised to turn in the state of  FIG. 9C . At the stage of  FIG. 9C , the second ratchet  105  is separated from the first ratchet  104 , but because the advancement of the first ratchet  104  is slow, the second ratchet  105  and the first ratchet  104  collide on the back sides  105   g  and  104   g  as shown in  FIG. 9D . 
   The second ratchet  105  is provided with the notch portion  105   e  as previously described, in which a whirl-stop projection  101   a  extending from the main frame portion  101  engages this notch portion. And there is a clearance  130   a  between the notch portion  105   e  and the projection  101   a , in which the rotation angle θ of the clearance  130   a  is equivalent to the rotation angle α of the back side  104   g  in the first ratchet  104  as shown in  FIG. 9C . 
   Thus, at the time of  FIG. 9D  when the back side  105   g  of the second ratchet  105  and the back side  104   g  of the first ratchet  104  collide, the second ratchet  105  is moved to the right in the figure. 
   An impact force at the time of collision is very small, because the second ratchet  105  gets rid of the first ratchet  104  upon a light collision, with a small loss of elastic energy. 
   Thereafter, the second ratchet  105  further moves forward in a direction to the first ratchet  104 , and moves to the right. Consequently, the second ratchet  105  and the first ratchet  104  collide on the front sides  105   f  and  104   f , as shown in  FIG. 9E . This collision has a great impact force of collision, because there is some loss due to a slight collision at the stage of  FIG. 9D , but the elastic energy of the spring  120  ( FIG. 8 ) urging the second ratchet  105  is almost employed. 
   And the second ratchet  105  is moved to the left due to the rotation of the first ratchet  104  at the stage of  FIG. 9F , so that the right side of the notch portion  105   e  is restrained by the left side of the projection  101   a . Thereafter, the second ratchet  105  restrained by the left side of the projection  101   a  is moved backward again due to the rotation of the first ratchet  104  as in  FIG. 9G . 
   At the low speed rotation of  FIGS. 9A–9G , if a left wall  105   k  of the notch portion  105   e  as shown in  FIG. 9B  and a left end  101   k  of the projection  101   a  collide, there is a loss in the elastic energy, so that the impact force in the state of  FIG. 9E  is weakened. Therefore, it is desirable that the rotation angle θ is set up so that the left wall  105   k  of the notch portion  105   e  and the left end  101   k  of the projection  101   a  may not collide. That is, the rotation angle θ is desirably greater than or equal to the amount that the second ratchet  105  is moved to the right from the time when the front sides  105   f  and  104   f  are separated as in  FIG. 9C  to the time when the front sides  105   f  and  104   f  collide as in  FIG. 9E . The amount of movement of the second ratchet  105  to the right is equivalent to the rotation angle α from the vertex of the back side  104   g  in a radial portion of the first ratchet  104  to the lowermost point subtracted by a relative angle rate between the first ratchet  104  and the second ratchet  105 . However, the relative angle rate between the first ratchet  104  and the second ratchet  105  is affected by the mass of the second ratchet  105  and the biasing force of the spring  120 , and is generally difficult to obtain. 
   Accordingly, supposing that the relative angle rate between the first ratchet  104  and the second ratchet  105  is zero at minimum, the rotation angle θ is set such that θ≧α. That is, the second ratchet is set such that when the first ratchet is in a stopped state, it is supported to be rotatable by an angle or more from the position at which the irregular face of the second ratchet overrides the irregular face of the first ratchet to the position at which the irregular face of the second ratchet engages the irregular face of the first ratchet most deeply. In this way, when the rotation angle rate A of the first ratchet  104  is considerably slow, the left side  105   k  of the notch portion  105   e  is not restrained by the left side  101   k  of the projection  101   a , so that the second ratchet  105  can move forward. 
   Also, the rotation angle may be set such that θ≧0.6α. That is, the second ratchet may be set such that when the first ratchet is in the stopped state, it is supported to be rotatable by 0.6 times an angle or more from the position at which the irregular face of the second ratchet overrides the irregular face of the first ratchet to the position at which the irregular face of the second ratchet engages the irregular face of the first ratchet most deeply. In this way, at the considerably slow rate, the left side  105   k  of the notch portion  105   e  and the left side  101   k  of the projection  101   a  collide, but the loss of elastic energy can be reduced. 
   Also, the rotation angle may be set such that θ≧0.3α. That is, the second ratchet may be set such that when the first ratchet is in the stopped state, it is supported to be rotatable by 0.3 times an angle or more from the position at which the irregular face of the second ratchet overrides the irregular face of the first ratchet to the position at which the irregular face of the second ratchet engages the irregular face of the first ratchet most deeply. In this way, at the slightly slow rate, the left side  105   k  of the notch portion  105   e  and the left side  101   k  of the projection  101   a  collide, but the loss of elastic energy can be reduced. 
   With first embodiment of the invention, a great impact force is obtained at the high and low speed rotation, whereby the impact drill having the excellent drilling ability is provided. 
   Second Embodiment 
     FIG. 10  shows a second embodiment of the invention, in which a width across flat  105   h  is provided in a part on the outer cylindrical portion  105   b  of the second ratchet  105 , the whirl-stop notch portion  101   b  is provided in the main frame portion  101 , and a clearance  103   b  is provided between the width across flat  105   h  and the whirl-stop notch portion  101   b . As a result, the second ratchet  105  can be rotated within a predetermined range, and operated in the same manner as in the first embodiment. 
   Third Embodiment 
     FIG. 11  shows a third embodiment of the invention, in which a projection  105   i  is provided in a part on the outer cylindrical portion  105   b  of the second ratchet  105 , a whirl-stop groove  101   c  is provided in the main frame portion  101 , and a clearance  130   c  is provided between the projection  105   i  and the whirl-stop groove  101   c . With this constitution, the second ratchet  105  can be rotated within a predetermined range, whereby there is the same effect as in the first embodiment. 
   Fourth Embodiment 
     FIG. 12  shows a fourth embodiment of the invention, in which the projection  105   i  is provided in a part on the outer cylindrical portion  105   b  of the second ratchet  105 , the whirl-stop groove  101   c  is provided in the main frame portion  101 , an elastic body  131  is disposed between the projection  105   i  and the whirl-stop groove  101   c , and the clearance  130   c  is provided between the projection  105   i  and the whirl-stop groove  101   c . With this constitution, the second ratchet  105  can be rotated within a predetermined range, and the elastic body  131  relieves the impact at the time of rotation, so that the vibration on the groove  101   c  is reduced. 
   Fifth Embodiment 
     FIG. 13  shows a fifth embodiment of the invention, in which a thrust bearing  132   a  is provided between a cylindrical bottom portion  105   c of the second ratchet  105  and the spring  120 . Also, a thrust bearing  133   b  is provided between the spring  120  and a side wall portion  122  extending from the main frame portion  101 . 
   With this constitution, even if the second ratchet  105  is rotated, a rolling friction with the spring  120  is reduced by the thrust bearing  132   a . Also, if the second ratchet  105  is rotated in a state except for the thrust bearing  133   b , the spring  120  is rotated together with the second ratchet  105 , but a rolling friction with the side wall portion  122  is reduced owing to existence of the thrust bearing  133 . 
   One or both of the thrust bearings  132   a  and  133   b  may be employed. Also, the thrust bearing  132   a ,  133   b  can be employed only with a ball. With this constitution, the rotation of the second ratchet  105  can be made smoother.