Electric power tool having an improved impact cushioning mechanism

• US 6,277,013 B1
• Filed: 10/04/1999
• Issued: 08/21/2001
• Est. Priority Date: 10/05/1998
• Status: Expired due to Term

• Current Assignee: Makita Corporation
• Original Assignee: Makita Corporation
• Inventors: Itakura, Toru, Sasaki, Katsuhiko, Sugiura, Shin
• Primary Examiner(s): Eley, Timothy V.
• Assistant Examiner(s): NGUYEN, DUNG V
• Application Number:
  US09/411,876
• Time in Patent Office: 687 Days
• Field of Search: 451/360, 451/344, 248/573, 248/579, 248/580, 188/68, 188/69, 188/73.38, 192/144, 192/146, 192/147, 192/148, 192/150, 192/56.1, 192/56.2
• US Class Current: 451/360
• CPC Class Codes: B24B 23/02 with rotating grinding tools; Accessories therefor
• CPC Class Codes: B24B 41/04 Headstocks; Working-spindles; Features relating thereto

Abstract

A grinder 1 includes a spindle 9 having a small-diameter section 11 and a medium-diameter section 12 and a motor shaft 5 on which a pinion gear 6 is provided. The grinder 1 further includes a bevel gear 18 which is provided on the small-diameter section 11 of the spindle 9 and engages the pinion gear 6, and a lock sleeve 17 provided below the bevel gear 18 on the medium-diameter section 12. A coupling groove 21 is provided in the lower surface of the bevel gear 18 opposing the upper surface of the lock sleeve 17. The coupling groove 21 has an external diameter coaxial with and equal to the inner diameter of the lock sleeve 17 and further has an inner diameter coaxial with and equal to the external diameter of the medium-diameter section 12. An inner coil spring 22 is fitted around the second peripheral surface such that half the length of the coil spring covers the inner peripheral surface of the coupling groove 21, whereas the other half covers the outer peripheral surface of the medium-diameter section 12. In addition, an outer coil spring 23 is fitted around the first peripheral surface such that half the length of the coil spring covers the outer peripheral surface of the coupling groove 21, whereas the other half covers the inner peripheral surface of the lock sleeve 17. The grinder 1 additionally includes a gear housing 3 and a locking device 25 for locking the bevel gear 18.

Claims

1. An electric power tool, comprising:

a motor having a motor shaft which is rotatable in a predetermined direction and includes a first section;

a first gear freely rotatably provided on the motor shaft, the first gear including a gear shaft which coaxially opposes the first section of the motor shaft and which has approximately the same diameter as that of the first section;

a second gear provided on a spindle, the second gear engaging the first gear in order to transmit torque from the motor to the spindle; and

a coil spring wound around the first section of the motor shaft and the gear shaft of the first gear, the coil spring having an approximately uniform cross-section and being wound in the direction opposite to the rotational direction of the motor shaft such that the coil spring transmits torque between the motor shaft and first gear.

2. An electric power tool in accordance with claim 1, wherein the coil spring has an inner diameter slightly smaller than the diameter of the first section of the motor shaft and the gear shaft of the first gear such that the first section is connected to the gear shaft by the winding force of the coil spring while the motor is inoperative.

3. An electric power tool in accordance with claim 2, wherein the tool further comprises

a housing,

a bearing for supporting the motor shaft, the bearing having an outer surface and being disposed in a portion of the housing,

a cylindrical elastic ring which is disposed between the bearing and said portion of the housing and which includes an inner surface and at least one protrusion provided on the inner surface, the at least one protrusion pressing the outer surface of the bearing when the elastic ring is disposed in place.

4. An electric power tool in accordance with claim 1, wherein the midpoint of the coil spring is located at the connection of the first section of the motor shaft and the gear shaft of the first gear, such that half the winding of the coil spring covers the first section and the other half of the winding covers the gear shaft.

5. An electric power tool in accordance with claim 4, wherein the tool further comprises

a housing,

a bearing for supporting the motor shaft, the bearing having an outer surface and being disposed in a portion of the housing,

a cylindrical elastic ring which is disposed between the bearing and said portion of the housing and which includes an inner surface and at least one protrusion provided on the inner surface, the at least one protrusion pressing the outer surface of the bearing when the elastic ring is disposed in place.

6. An electric power tool in accordance with claim 1, wherein the coil spring has an approximately square cross section.

7. An electric power tool in accordance with claim 6, wherein the tool further comprises

a housing,

a bearing for supporting the motor shaft, the bearing having an outer surface and being disposed in a portion of the housing,

a cylindrical elastic ring which is disposed between the bearing and said portion of the housing and which includes an inner surface and at least one protrusion provided on the inner surface, that at least one protrusion pressing the outer surface of the bearing when the elastic ring is disposed in place.

8. An electric power tool in accordance with claim 1, wherein the motor shaft further includes a free end and a second section which has a diameter smaller than that of the first section and is terminated at the free end, and further wherein the first gear further includes an axial bore having approximately the same inner diameter as the diameter of the second section of the motor shaft so as to allow the first gear to be freely rotatably provided around the second section of the motor shaft at the free end of the motor shaft.

9. An electric power tool in accordance with claim 8, wherein the first gear further includes a tooth section having a diameter larger than that of the gear shaft, and further wherein the tool further comprises a means for limiting movement of the coil spring in one axial direction of the spring, the coil spring fitted between the limiting means and the tooth section, thus prohibiting the axial movement of the coil spring in either direction.

10. An electric power tool in accordance with claim 9, wherein the means for limiting is a side surface of the bearing.

11. An electric power tool in accordance with claim 8, wherein the tool further comprises

a housing,

a bearing for supporting the motor shaft, the bearing having an outer surface and being disposed in a portion of the housing,

a cylindrical elastic ring which is disposed between the bearing and said portion of the housing and which includes an inner surface and at least one protrusion provided on the inner surface, the at least one protrusion pressing the outer surface of the bearing when the elastic ring is disposed in place.

12. An electric power tool in accordance with claim 1, wherein the tool further comprises

a housing,

a bearing for supporting the motor shaft the bearing having an outer shaft surface and being disposed in a portion of the housing,

a cylindrical elastic ring which is disposed between the bearing and said portion of the housing and which includes an inner surface and at least one protrusion provided on the inner surface, the at least one protrusion pressing the outer surface of the bearing when the elastic ring is disposed in place.

13. An electric power tool in accordance with claim 12, wherein the at least one protrusion of the elastic ring is a circular ridge formed around the inner surface of the elastic ring.

14. An electric power tool in accordance with claim 13, wherein said portion of the housing is a stepped recess for seating the elastic ring and the bearing.

15. An electric power tool in accordance with claim 14, wherein the housing comprises first and second casings divided at a position where the stepped recess is exposed, with the stepped recess being provided in the first casing and the second casing covering the stepped recess except where the motor shaft penetrates when assembled to the first casing.

16. An electric power tool in accordance with claim 1, wherein the first gear is a pinion gear and the second gear is a bevel gear, and further wherein the motor shaft is oriented orthogonal to the spindle.

17. An electric power tool in accordance with claim 16, wherein the tool is a grinder further comprising a grinding wheel attached to a free end of the spindle outside the housing.

18. An electric power tool, comprising:

a housing;

a motor having a motor shaft which is rotatable in a predetermined direction and includes a first section;

a bearing for supporting the motor shaft, the bearing having an outer surface and being disposed in a portion of the housing;

a first gear freely rotatable provided on the motor shaft, the first gear including a gear shaft which coaxially opposes the first section of the motor shaft and which has approximately the same diameter as that of the first section;

a second gear provided on a spindle, the second gear engaging the first gear in order to transmit torque from the motor to the spindle;

a coil spring wound around the first section of the motor shaft and the gear shaft of the first gear, the coil spring being wound in the direction opposite to the rotational direction of the motor shaft such that the coil spring transmits torque between the motor shaft and first gear; and

a cylindrical elastic ring which is disposed between the bearing and said portion of the housing and which includes an inner surface and at least one protrusion provided on the inner surface, that at least one protrusion pressing the outer surface of the bearing when the elastic ring is disposed in place.

19. An electric power tool, comprising:

a motor having a motor shaft which is rotatable in a predetermined direction and includes a first section;

a first gear freely rotatably provided on the motor shaft, the first gear including a gear shaft which coaxially opposes the first section of the motor shaft and which has approximately the same diameter as that of the first section;

a second gear provided on a spindle, the second gear engaging the first gear in order to transmit torque from the motor to the spindle; and

a coil spring wound around the first section of the motor shaft and the gear shaft of the first gear, the coil spring being wound in the direction opposite to the rotational direction of the motor shaft such that the coil spring transmits torque between the motor shaft and first gear;

wherein the midpoint of the coil spring is located at the connection of the first section of the motor shaft and the gear shaft of the first gear, such that half the winding of the coil spring covers the first section and the other half of the winding covers the gear shaft.

20. An electric power tool, comprising:

a motor having a motor shaft;

a housing;

a bearing for supporting the motor shaft, the bearing having an outer surface and being disposed in a portion of the housing; and

a cylindrical elastic ring which is disposed between the bearing and said portion of the housing and which includes an inner surface and at least one protrusion provided on the inner surface, the at least one protrusion pressing the outer surface of the bearing when the elastic ring is disposed in place.