String trimmer and trimming head thereof

Patent metadata

Field	Value
Publication number	US-12408583-B2
Application number	US-202117551282-A
Country	US
Kind code	B2
Filing date	Dec 15, 2021
Priority date	Jun 17, 2019
Publication date	Sep 9, 2025
Grant date	Sep 9, 2025

Abstract

A string trimmer includes a trimming head, a driving device, and an operating device. The trimming head includes a spool, a head housing formed with an accommodating space, and a transmission member mounted to the spool that can move freely between the head housing and the spool in the direction of a straight line perpendicular to the direction of the rotation axis. The trimming line has an effective portion extending from the accommodating space. When the length of the effective portion of the trimming line is larger than a preset value, the transmission member automatically releases the head housing. When the length of the effective portion of the trimming line is less than the preset value, the transmission member locks the head housing.

First claim

What is claimed is:

1. A string trimmer, comprising:
a trimming head comprising:
a spool for winding a trimming line, the spool comprising an outer surface having a limiting portion extending upwards from the outer surface, the limiting portion defining a channel;
a head housing defining an accommodating space for at least partially accommodating the spool, the head housing comprising an outer housing surface defining an aperture though which the limiting portion extends, a circumference of the aperture including a plurality of mating portions extending from the outer housing surface, the plurality of mating portions including a driving portion having an inclined surface and a plane defined by the inclined surface;
a transmission member slidably coupled to the spool within the channel, the transmission member comprising the driving portion, the transmission member having a first position where the driving portion mates with at least one of the plurality of mating portions of the head housing to prevent relative rotation between the spool and the head housing and a second position where the driving portion does not mate with at least one of the plurality of mating portions of the head housing to allow relative rotation between the spool and the head housing;
a biasing element for biasing the transmission member towards the first position; and

a driving device comprising a motor for driving the trimming head to rotate around a rotation axis, and the plane defined by the inclined surface does not pass through the rotation axis,
wherein when the transmission member is in the first position, the trimming head is in a working state and the transmission member rotates around the rotation axis synchronously with the spool, and when the transmission member is in the second position, the trimming head is in a autonomous line-feeding state and relative rotation is generated between the spool and the head housing to feed the trimming line, and
when the trimming head is driven to rotate by the motor, the transmission member is subjected to a centrifugal force which cause a moving tendency in a direction from the first position to the second position, when the head housing rotates around the rotation axis, friction generated between the transmission member and the limiting portion applies a resistance to the transmission member against the centrifugal force to prevent the transmission member from moving from the first position to the second position, and when the trimming head is in a trimming state and a length of an effective portion of the trimming line extending beyond the head housing is less than a preset value, the resistance applied by the head housing to the transmission member is reduced so that the transmission member moves from the first position to the second position under the centrifugal force.

2. The string trimmer according to claim 1 , wherein, when the length of the effective portion of the trimming line is greater than the preset value, the transmission member is in the first position and, when the length of the effective portion of the trimming line is less than the preset value, the transmission member is in the second position.

3. The string trimmer according to claim 1 , wherein the limiting portion is defined by two upstanding walls symmetrically arranged with respect to the rotation axis, the limiting portion is formed with a sliding rail for the transmission member to slide, and the limiting portion comprises a contact surface in a straight line perpendicular to the rotation axis.

4. The string trimmer according to claim 1 , wherein the spool further comprises a receiving groove, the biasing element is arranged in the receiving groove, a first end of the biasing element abuts against the receiving groove, and a second end of the biasing element abuts against the transmission member.

5. The string trimmer according to claim 1 , wherein the trimming head further comprises an automatic winding state, when the trimming head is in the automatic winding state, the motor drives the spool to rotate relative to the head housing in a second rotation direction so that the trimming line is wound to the spool and, when the trimming head is in the autonomous line-feeding state, the transmission member moves to the second position and the spool rotates relative to the head housing along a first rotating direction to release the trimming line.

6. The string trimmer according to claim 1 , wherein the string trimmer further comprises a damping device for damping at least one of the spool or the head housing to make the string trimmer in an automatic winding state.

7. The string trimmer according to claim 1 , wherein the plane defined by the inclined surface is parallel to the rotation axis, and a distance between the rotation axis and the plane is greater than zero.

8. The string trimmer according to claim 1 , wherein a distance between the rotation axis and the plane defined by the inclined surface is greater than 0 mm and less than or equal to 20 mm.

9. The string trimmer according to claim 7 , wherein the inclined surface is capable of applying a reaction force, the inclined surface has a projection line in the plane defined by the inclined surface and perpendicular to the rotation axis, the projection line comprises a first extreme position and a second extreme position, and a central angle between a connecting line between the first extreme position and the rotation axis and the connecting line between the second extreme position and the rotation axis is greater than 0° and less than or equal to 45°.

10. The string trimmer according to claim 9 , wherein the string trimmer further comprises a first circumference centered on the rotation axis and passing through the first extreme position and a second circumference centered on the rotation axis and passing through the second extreme position, an angle γ formed by a tangent line of the first circumference at a first extreme position, and a tangent line of the second circumference at the second extreme position is less than or equal to 45°.

11. The string trimmer according to claim 1 , wherein, when the transmission member is in the first position, the trimming head is in the trimming state and the motor has a first rotation speed and, when the transmission member is in the second position, the trimming head is in the autonomous line-feeding state, the motor has a second rotation speed, a ratio of an absolute value of a difference between the first rotation speed and the second rotation speed to the first rotation speed is greater than or equal to 0 and less than or equal to 0.1, and the relative rotation is generated between the spool and the head housing to feed the trimming line.

12. A trimming head, used for a string trimmer, capable of being driven to rotate around a rotation axis to achieve grass trimming, comprising:
a spool for winding a trimming line the spool comprising an outer spool surface having a limiting portion extending upwards from the outer spool surface, the limiting portion defining a channel;
a head housing forming an accommodating space for at least partially accommodating the spool, the head housing comprising an outer head housing surface defining an aperture though which the limiting portion of the spool extends, a circumference of the aperture including a plurality of mating portions extending from the outer head housing surface, the plurality of mating portions including a driving portion having an inclined surface and a plane defined by the inclined surface; and
a transmission member slidably coupled to the spool within the channel, the transmission member having a first position where the driving portion mates

Assignees

• Nanjing Chervon Ind Co Ltd

Inventors

• Guo Jianpeng

Classifications

• A01D2101/00

  Lawn-mowers · CPC title

• A01D34/4166

  Mounting or replacement of the lines · CPC title

• A01D75/20

  Devices for protecting men or animals · CPC title

• A01D69/06

  Gearings · CPC title

• A01D34/4162 Primary

  automatically · CPC title