CA-3126071-C - A HANDHELD CUT-OFF SAW FOR CUTTING CONCRETE AND STONE, COMPRISING A DRIVE ARRANGEMENT FOR DRIVING A CIRCULAR CUTTING TOOL

Abstract

A handheld cut-off saw (300) for cutting concrete and stone, the handheld cut-off saw comprising a drive arrangement (100, 200, 600, 800) for driving a circular cutting tool (110), the drive arrangement comprising: a belt drive portion (120) comprising a first pulley (121) and a second pulley (122), wherein the first pulley is arranged to be powered by a power source (130) and to drive the second pulley via a belt (123), wherein the second pulley (122) has a larger pitch diameter than the first pulley (121); and a gear transmission portion (140) comprising a first gearwheel (141) and a second gearwheel (142), wherein the first gearwheel (141) is co-axially connected to the second pulley (122) and radially connected to the second gearwheel (142), and wherein the second gearwheel (142) is arranged to be co-axially connected to the circular cutting tool (110).

Inventors

• Hakan Pinzani
• Niklas Sundberg
• Fredrik Karlsson

Assignees

• HUSQVARNA AB

Dates

Publication Date

20260505

Application Date

20200220

Priority Date

20190221

Claims (20)

1. 19 CLAIMS 1. A handheld cut-off saw for cutting concrete and stone, the handheld cut-off saw comprising a drive arrangement for driving a single blade circular cutting tool, the drive arrangement comprising: a belt drive portion comprising a first pulley and a second pulley, 5 wherein the first pulley is arranged to be powered by a power source and to drive the second pulley via a belt, wherein the second pulley has a larger pitch diameter than the first pulley; and a gear transmission portion comprising a first gearwheel and a second 10 gearwheel, wherein the first gearwheel is co-axially connected to the second pulley and radially connected in direct meshing engagement to the second gearwheel, and wherein the second gearwheel is arranged to be co-axially connected to the single blade circular cutting tool.
2. 2. The handheld cut-off saw according to claim 1, wherein a distance (D1) from a 15 center axis of the first pulley to a center axis of the second pulley is smaller than a distance (D2) from the center axis of the first pulley to a center axis of the second gearwheel.
3. 3. The handheld cut-off saw according to any one of claim 1 or 2, wherein the second gearwheel has a larger pitch diameter compared to the first gearwheel. 20
4. 4. The handheld cut-off saw according to claim 3, wherein a ratio of the first gearwheel pitch diameter and the second gearwheel pitch diameter is between 0.4 and 0.6.
5. 5. The handheld cut-off saw according to claim 4, wherein a ratio of the first gearwheel pitch diameter and the second gearwheel pitch diameter is 0.56. 25
6. 6. The handheld cut-off saw according to any one of claims 1 to 5, wherein the first gearwheel has a pitch diameter between 20 and 35 mm, and wherein the second gearwheel has a pitch diameter between 40 and 60 mm.
7. 7. The handheld cut-off saw according to claim 6, wherein the first gearwheel has a pitch diameter is 28 mm, and wherein the second gearwheel has a pitch diameter is 50 mm.
8. 8. The handheld cut-off saw according to any one of claims 1 to 7, wherein the second gearwheel has a pitch diameter smaller than a pitch diameter of the second 5 pulley.
9. 9. The handheld cut-off saw according to claim 1 or 2, wherein the second gearwheel has an equal or smaller pitch diameter compared to the first gearwheel.
10. 10. The handheld cut-off saw according to any one of claims 1 to 9, wherein a ratio between a pitch diameter of the first pulley and a pitch diameter of the second 10 pulley is between 0.4 and 0.6.
11. 11. The handheld cut-off saw according to any one of claims 1 to 10, wherein a ratio between a pitch diameter of the first pulley and a pitch diameter of the second pulley is 0.55.
12. 12. The handheld cut-off saw according to claim 11, wherein the first pulley has a 15 pitch diameter between 30 and 40 mm, and wherein the second pulley has a pitch diameter between 60 mm and 70 mm.
13. 13. The handheld cut-off saw according to claim 12, wherein the first pulley has a pitch diameter is 35.4 mm, and wherein the second pulley has a pitch diameter is 64.85 mm. 20
14. 14. The handheld cut-off saw according to any one of claims 1 to 13, wherein a drive ratio of the drive arrangement is between 1:3 and 1:4.
15. 15. The handheld cut-off saw according to claim 14, wherein the drive ratio of the drive arrangement is between 1:3.0 and 1:3.5.
16. 16. The handheld cut-off saw according to claim 15, wherein the drive ratio of the 25 drive arrangement is 1:3.2.
17. 17. The handheld cut-off saw according to any one of claims 1 to 16, wherein the belt drive portion belt is a toothed belt. 21
18. 18. The handheld cut-off saw according to any one of claims 1 to 17, wherein the belt drive portion belt is a v-belt.
19. 19. The handheld cut-off saw according to any one of claims 1 to 18, wherein the power source is an electric motor.
20. 20. The handheld cut-off saw according to any one of claims 1 5 to 18, wherein the power source is a combustion engine or a hybrid electric combustion engine.

Description

TITLE A HANDHELD CUT-OFF SAW FOR CUTTING CONCRETE AND STONE, COMPRISING A DRIVE ARRANGEMENT FOR DRIVING A CIRCULAR CUTTING TOOL TECHNICAL FIELD 5 There are disclosed drive arrangements for powering rotatable work tools. The present disclosure relates mainly to power tools such as cut-off saws. BACKGROUND Dust is often generated in large amounts when cutting concrete, stone, and other hard 10 materials using a power tool. Such air-borne dust can be harmful to an operator and often necessitates extensive cleaning of the workplace after cutting. It is therefore desired to minimize the amount of air-borne dust. Water or other liquids can be added to the cutting tool during the cutting operation to bind the airborne dust. This makes the cutting environment less harmful to the 15 operator, and also prevents the airborne dust from spreading over a large area. It is known to arrange a liquid dispensing system on a power tool in order to reduce the amount of generated dust. US 9,604,297 B2 discloses a liquid dispensing system for adding a controlled amount of liquid to a rotatable work tool. However, it is not always desirable or even possible to add liquid during the cutting 20 operation. Dry cutting is then an option. When dry cutting a material with a power tool, it is advantageous to reduce the rotational speed of the tool, since a reduced blade speed does not propel dust particles as much and therefore makes it easier to collect the generated dust using, e.g., a vacuum system or the like. Unfortunately, power sources such as electrical motors and combustion engines 25 operating at reduced engine speeds are more costly and often also weighs more than standard motors operating around 9000-10000 revolutions per minute (rpm). Various forms of transmission systems having a gear ratio for lowering the speed of the motor drive shaft are therefore often used in dry cutting power tools. It is known to reduce blade speed using a drive belt with a smaller pulley connected to 30 the motor drive shaft and a larger pulley connected to the work tool. However, having WO 2020/171766 2 PCT/SE2020/050197 a large pulley close to the work tool may negatively impact the achievable cutting depth of the tool. Also, the belt will be subject to a large torque force, which increases requirements on belt dimensions. There is a need for power tool drive arrangements which provide reduced blade speeds 5 while maintaining cutting depth, and which do not require reducing engine drive shaft speeds. SUMMARY It is an object of the present disclosure to provide improved drive arrangements, power 10 tools, and methods which allow for reduced blade speeds. It is a further object of the present disclosure to optimize cutting depth. These objects are at least in part obtained by a drive arrangement for driving a rotatable work tool. The drive arrangement comprises a belt drive portion with a first pulley and a second pulley. The first pulley is arranged to be powered by a power 15 source and to drive the second pulley via a belt. The second pulley has a larger pitch diameter than the first pulley. The drive arrangement also comprises a gear transmission portion comprising a first gearwheel and a second gearwheel. The first gearwheel is co-axially connected to the second pulley and radially connected to the second gearwheel. The second gearwheel is arranged to be co-axially connected to 20 the rotatable work tool. Thus, as the first pulley is rotated, force is transferred to the work tool via the belt and gears. The work tool is brought in rotation in an opposite direction compared to the first pulley. This drive arrangement provides for an efficient way to reduce tool speed down to 25 speeds suitable for dry cutting operation. The generated dust is propelled at reduced speed, giving slower moving dust particles that are more easily handled, which is an advantage. The combination of belt drive and gear transmission allow for design freedom, as will be exemplified in the below detailed description. For instance, the requirements on belt 30 drive dimensions can be relaxed due to the gear transmission portion. Also, the work WO 2020/171766 3 PCT/SE2020/050197 tool can be stopped abruptly without exerting excessive forces on, e.g., the belt drive portion. By means of the disclosed drive arrangement, requirements on engine power output can be relaxed, which is an advantage. 5 According to aspects, the second gearwheel has a pitch diameter smaller than a pitch diameter of the second pulley. A smaller second gearwheel diameter provides for an increased cutting depth, which is an advantage. According to some aspects, a distance D1 from a center axis of the first pulley to a center axis of the second pulley is smaller than a distance D2 from the center axis of 10 the first pulley to a center axis of the second gearwheel. In other words, the second pulley has been moved away from the cutting edge of the tool. The large second pulley therefore no longer limits t