SE544912C2

SE544912C2 - Pulse mechanism for Power Tool

Info

Publication number: SE544912C2
Application number: SE2130114A
Authority: SE
Inventors: Christian Friberg
Original assignee: Atlas Copco Ind Technique Ab
Priority date: 2021-04-28
Filing date: 2021-04-28
Publication date: 2022-12-27
Also published as: SE2130114A1; WO2022228851A1; DE212022000190U1; JP3246283U

Abstract

Disclosed herein is a hydraulic power tool for tightening by applying torque pulses to a fastener, the hydraulic power tool comprising a hydraulic coupling mechanism (110, 10, 10') comprising a first part (116, 16) comprising a passive space (120, 20) and a cylinder (130, 30) being configured to be driven by a motor shaft, a second part (114, 14) comprising an anvil configured to be coupled to the fastener for applying torque pulses to the fastener and an active space (122, 22), a gap (118, 18, 18') arranged between the first part and the second part interconnecting the passive space and the active space, wherein the active space (122, 22) is filled with oil and the passive space (120, 20) is filled with oil and air, and further comprising a capillary mechanism (36, 36', 36'') arranged at the gap to keep the oil in the gap using capillary force.

Description

Technical Fïeld The invention relates to the field of power tools comprising a pulse mechanism, in particular a hydraulic pulse mechanism having' a hydraulic coupling' mechanisn1 for applying' torque pulses onto an anvil that is connected to the output shaft of the power tool in order to transfer the torque onto a fastener, for instance via a bit-adapter or chuck.

Background of the Invention Typically, power tools for tightening are discontinuous devices that apply torque in small steps rather than in one continuous blow. When the fastener is running free, the power tool does not apply pulses and the driveshaft or output shaft spins fast and continuous. Once the fastener or bolt starts to tighten the work piece thus as soon as the bolt meets resistance and requires torque to rotate further, the tool begins pulsing, which means applying short bursts of torque that only last a short period. of time, so called torque pulses.

The source of the pulses in a pulse tool is a hydraulic pulse mechanism that consists of two rotating, cylindrical parts.

The first part driven by the motor can have an inner chamber filled with hydraulic fluid. The first part is connected to the power tool's motor. The second part, typically called the anvil, fits inside the first part. The anvil is connected to the tool's driveshaft and is bisected by two rolls or blades that are pushed outward by springs. These rolls or blades separate the chamber into two halves. As the first part rotates, the anvil's blades contact the inner wall of the inner chamber, which can either have engaging members on an inner' wall for engaging' the anvil or which. can. be formed the asymmetric. When the power tool is running at free speed,first part and. the second. part thus the anvil rotate in unison. At this point in the cycle, the rolls or blades are not engaging' the inner wall of the inner chamber or the engaging members and there is no pressure on the hydraulic fluid. As the fastener provides resistance to rotation, the anvil begins to slow, but the first part and the inner chamber continue rotating at its original speed. The blades or rolls are then pushed inward either due to the asymmetric shape of the inner chamber or the engaging members toward the anvil's center, compressing' the springs. This reduces the volume within the chamber and increases pressure on the hydraulic fluid.

When the first part and the inner chamber continues to rotate, hydraulic pressure in the fluid accumulates and the anvil rotation begins to hesitate slightly. Hydraulic pressure increases, pushing against the rolls or blades and forcing the anvil to rotate. When the hydraulic fluid reaches maximun1 pressure the anvil stops rotating. At this point rotational forces on the anvil are maximized.

When the anvil is pushed past this point and begins to move forward, the rolls or blades are pressed outward again, the hydraulic pressure drops, and the anvil accelerates, starting another pulse cycle.

The advantage of the pulse tool design is that the hydraulic fluid absorbs most of the vibration from the fastening process. Because torque is applied intermittently in rapid short pulses, torque reaction. is small and therewith the ergonomics of the operator are not compromised.

In such power tools the inner chamber where the blades or rolls are arranged needs to be filled 100% with oil to Üprovide optimal function. The inner chamber is also called active space or active chamber. When the power tool is used in industrial environments then the oil in the inner chamber or active space typically increases in temperature and therewith volume and thus a small hole is provided at the periphery of the inner chamber so that the oil can escape via a thin channel to a passive space containing air and a little oil, when the oil is heated up and therewith expands. This way the pressure in the inner chamber is kept constant and the function of the tool is the same even if the oil temperature in the active chamber increases or decreases for that matter. Oil is pressed back from the passive space into the active space when the power tool is used again and the centrifugal force provided by the motor shaft on which side the passive space is arranged is pressing the oil back into the active space via the gap and the small hole and the use of centrifugal force from the motor shaft that is driving the first part. In known power tools the gap has a constant width of about lmm. This gap and the width can lead to air entering the active space as described below. Typically the gap has a shape that is similar or the same as the lateral surface of a cone or a cut cone. solution is that in A. drawback with the above-described certain situations, thus when the power tool is oriented upside down or at certain angles or in particular with the drive shaft upwards relative to the gravitational force, then air can be drawn back into the active space via the small hole and the gap when the oil in the active space is cooling down. When air or air bubbles are entering the active space and thus the high-pressure area of the power tool, then the hydraulic coupling mechanism does not and cannot work as it should. In particular the first few rotations and therewith the first few tightenings after a rest period of the powertool pose problems, since the above-described centrifugal process takes a few rotations and therewith tightenings of fasteners until the air is pressed out of the passive space and oil entered the active space via the gap and the small hole. During these tightenings the power tool does not work accurately and properly. If the air bubbles take themselves to the wrong place in the power tool then the torque-pulse is interrupted at a stage where it is not fully completed, which means a weaker torque pulse. This can affect the torque measurement and therewith lead to fasteners or clamping forces that do not have the right target value.

A problem of prior art hydraulic power tools is thus that air can enter the active space via the gap and the small hole.

Summary of the Invention An object of the present invention is to provide a hydraulic power tool for tightening of fasteners that is reliable and robust.

The inventor of the present invention has realized that the key to a reliable and robust hydraulic power tool is to ensure that a gap between a hole leading to an active space containing oil and. a passive space containing air and a little bit of oil is always saturated with oil no matter the orientation of the hydraulic power tool. This can be achieved by the use of a capillary' mechanism. or capillary effect either by making' the gap smaller towards the small hole arranged at the periphery of the gap and the active space thus interconnecting the active space and the gap or by providing a wick structure in the gap or a combination thereof. The inventor realized that using any of these two solutions ensures that the gap is always filled with oil no matter the orientation of the hydraulic power tool. A gapfilled with oil prevents air from entering the active space and therewith provides a hydraulic power tool with very good reliability and robustness.

Disclosed herein is a hydraulic power tool for tightening by applying' torque pulses to a fastener, the hydraulic power tool comprising a hydraulic coupling næchanism and a nwtor with a motor shaft, the hydraulic coupling mechanism comprising: a first part comprising a passive space and a cylinder with at least one projection, the cylinder being configured to be driven by the motor shaft; a second part comprising an anvil configured to be coupled to the fastener for applying torque pulses to the fastener, an active space, at least one hole arranged at a periphery of the active space, at least one movable engaging element for engagement with the at least one projection of the cylinder, the engaging elements and the at least one projection being arranged in the active space; a gap arranged between the first part and the second part interconnecting the passive space and the active space via the at least one hole, wherein. the active space is filled with oil and the passive space is filled with oil and air. The hydraulic power tool further comprises a capillary mechanism arranged at the gap, said capillary mechanism keeping the oil in the gap using capillary force so that the active space is in any circumstance filled with oil independent of the orientation of the power tool, oil temperature, surrounding and/or tool temperature and/or other circumstances such as vibrations and/or impacts. ÜThe advantage of the above-described embodiment is that the gap is always saturated with oil and therewith air cannot enter the active space.

In an embodiment the capillary' mechanisn1 is configured. to draw oil via capillary force in the direction of the hole and the active space, respectively.

The direction of the force provided by the capillary mechanism helps to ensure that the oil is not being drawn away from the active space. This is also ensured since the active space only comprises oil and since passive space comprises oil and air/gas. An increase in oil temperature due to the hydraulic power tool being at work will lead to oil being pushed out of the active space due to expansion and then, when the oil is cooling down therewith reducing its volume, the capillary mechanism is drawing oil back into the active space due to capillary force or capillary effect.

In an embodiment the gap is at least partially shaped like a lateral surface of a cone or a cut cone.

The shape of the gap is typically given by the shape of the first part and the second part respectively.

The shape of the gap is rotationally symmetric around an axis defined by the motor shaft.

The liquid- or oil pressure in the active space is higher than the pressure in the passive space.

This ensures the accurate delivery of torque pulses.

In an embodiment the capillary mechanism. may be a wick structure that is shaped according to the gap so that it canbe placed snug in the gap configured to draw oil towards the active space.

A wick structure is easy to realize and can even be built into existing and used hydraulic power tools.

The wick structure may at least partially be shaped like a lateral surface of a cone.

The wick structure may further fit snug into the gap.

In an embodiment the wick structure may further comprise a projection that reaches to a bottom of the passive space and that is also designed to fulfill a wick function, so that the wick structure is always saturated with oil.

In another embodiment the wick structure may' be made of metal, such as perforated metal in order to generate capillary force.

The metal may be aluminum.

This provides for a robust and durable wick structure.

In a further embodiment the wick structure may be made of fabric such. as cotton, glass fiber* or any other suitable fiber material such as carbon or a combination thereof.

In another embodiment the capillary mechanism may be a continuously decreasing width in the gap towards the hole.

With such a solution for the capillary mechanism the assembly of the hydraulic power tool may be simplified.In another embodiment the width in the gap may be chosen to be O.6nm1 to lmm. at a first end. of the gap close to the passive space and O.5mm to O.lmm at a second end of the gap close the active space, preferably 0.6 to O.8mm at the first end and 0.3 to O.lmm at the second end.

This way the capillary force increases towards the hole and the active space thus ensuring that there is always oil or liquid present close to the hole and therewith the active space.

Further disclosed herein may be a wick structure that is suitable to be used in a hydraulic power tool according to the above.

The wick structure may even be employed in the solution where the gap has a continuously decreasing width towards the hole and the active space, respectively.

The following terms used in this document are herewith explained in more detail: Wick Structure The term wick structure describes a wick element that can draw a liquid using capillary force similar to a wick in an oil lamp. The wick structure may be made of various materials, such as metal, fabric, carbon or any other potentially suitable material. The shape of the wick structure is typically adapted to the shape of the gap between the first part and the second part, which is typically a circular symmetric geometrical shape such as the lateral surface of a cone or the lateral surface of a cut cone. In embodiments the wick structure may even be shaped as a part of the lateral surface of a sphere.

Capillary Force The term capillary force used herein describes the phenomena of the capillary effect discovered. by Leonardo da Vinci, which capillary effect describes the flowing of a liquid in narrow spaces without or even opposite gravitational force. The capillary force or effect because capillary occurs of intermolecular forces between the liquid and surrounding solid surfaces. If a diameter of a tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and tube wall act to propel the liquid and make if flow along the tube or narrow space.

Lateral surface of a cone/Lateral surface of a cut cone The term lateral surface of a cone or lateral surface of a cut cone used herein describes a shape that corresponds to a lateral surface of a cone or a lateral surface of a cone where the top is cut thus cut cone. The wick structure and the gap may at least partially have such a shape.

Capillary Mechanism The term capillary mechanism used herein describes any mechanism that uses the capillary effect for drawing liquid, in the described. case oil, towards a space, such as the active space so that air cannot enter the active space. The capillary mechanism described herein provides a directed capillary force towards the active space. Due the presence of air in the passive space the liquid or oil will always be drawn towards the active space since the capillary force is not strong enough to draw liquid or oil from the active space and generate a vacuum there.

Brief Description of the Drawings The present invention will now be described, for exemplary purposes, in more detail by way of an embodiment(s) and with reference to the enclosed drawings, in which: Fig. 1 schematically illustrates a cross sectional view onto a hydraulic power tool according to the prior art; cross sectional Fig. 2 schematically illustrates a view onto a hydraulic coupling' mechanisn1 of a hydraulic power tool according to figure 1; Fig. 3 schematically illustrates a cross sectional view onto a hydraulic coupling mechanism according to an embodiment of the invention; Fig. 4 schematically illustrates a perspective onto a wick structure according to an embodiment of the invention; Fig. 5 schematically illustrates a cross sectional view onto a hydraulic coupling mechanism according' to another* embodiment of the present invention; and Fig. 6 schematically illustrates a cross sectional view onto a wick structure according to another embodiment of the present invention.

Detailed Description The invention will now be described in more detail referring to figures 1 and 6, whereby' figures 1 and. 2 disclose a hydraulic power tool 100 according' to the prior art. The hydraulic power tool 100 comprises a housing 102, a handle 104, a motor unit 106 with a motor 108 and hydraulic coupling mechanism 110 for coupling a motor shaft 112 to an anvil or second. part 114. The motor 108 further comprises a motor shaft 132 that is coupled to a first part 116 (c.f. figure 2) of the hydraulic coupling mechanism 110. The hydrauliccoupling mechanism 110 is configured to deliver torque pulses via the anvil or second part 114 to a fastener (not shown). The hydraulic coupling mechanism 110 is shown in more detail in figure 2. It comprises the first part 116 and the second part 114 that are coupled to one another via a cylinder 130 comprising two projections 124 extending into an active space 122 for engagement with. engaging' elements in the form. of blades or rolls 126 of the anvil or second part 114. The engaging elements 126 are embedded so that they can elastically' move towards a center axis A defined. by the rotational axis of the motor 108 and the motor shaft 132 respectively. The first part 116 and the second part 114 are coupled to one another via the cylinder 130 that is either coupled or integrally formed with the first part 116. Between the first and second part 116, 114 a gap 118 is arranged. The gap 118 interconnects the active space 122 and. a passive space 120 arranged. in the first part 116 via za hole (not shown in figure 2) at the periphery of the active space 122. The active space 122 or active chamber 122 is filled with oil only and the passive space 120 is filled with oil and air. The gap 118 can in this solution be filled with oil or air.

The gap 118 has a constant width of about 1mm.

When the hydraulic power tool 100 and the hydraulic coupling mechanism 110 are in use then the cylinder 130 applies torque pulses to the second part 114 or anvil via the projections 124 onto the engaging elements 126 of the second part 114. As long as the second part 114 and therewith the fastener is running free the engaging element 126 stay engaged on the projections 124 due to the elastic embedding, for example via and due to the oil pressure in the active space llsprings, When the second part meets torque resistance then engaging elements are pushed inward towards the axis A andthe cylinder 130 can rotate freely around half a rotation until the engaging elements 126 hit the projections 124 again and deliver a torque pulse. This process is repeated until the correct torque is applied to the fastener via the second part 114. During this process many torque pulses are applied and therewith the oil in the active space 122 is compressed and released several times over thereby increasing its temperature and therewith leading to a volume expansion of the oil in the active space 122. Since a substantial pressure change in the active space 122 would. lead. to a hydraulic power tool 100 that is not functioning properly, the oil can expand via the hole (c.f. figure 3) into the gap 118 and the passive space Once the hydraulic power tool 100 is not used any longer the oil in the active space 122 is cooling down and therewith at least in the ideal case, via shrinking drawing back oil, the gap 118 and. the passive space Depending' on the orientation of the hydraulic power tool 100 air or air thebubbles can be drawn back into the active space 120 via gap 118 and the hole, leading to a hydraulic power tool that is not working properly. This can be avoided by the idea of the invention as now described referring to figures 3 to In general it can be said that the hydraulic coupling mechanism 10 shown in figure 3 is similarly built as then one in illustrated in figures 1 and 2 with the difference that the gap 18 is designed differently. The embodiment shown in figure 3 is for the sake of simplicity shown with certain parts, such as the engaging elements 126 and the projections 124 removed. The hydraulic coupling mechanism 10 comprises a first part 16, a second part 14 coupled to the first partvia a cylinder 30, which is rigidly and fixedly connected tothe first part 16. The cylinder 30 comprises projections (not shown in figure 3) that can engage with engaging elements (not shown in figure 3), such as rolls or blades, of the second part 16 or anvil for providing torque pulses to a fastener connected to the second part 14. The function of the hydraulic coupling mechanism illustrated in figure 3 is similar to the one illustrated in figures 1 and 2 and will not be described again herewith.

An active space 22 or active chamber arranged. inside the cylinder 30 and. also delimited. by the second. part 14 is illustratedd The active space 22 is coupled. to a passive space 20 in the first part 16 via a hole 28 and a gap 18. The hole 28 is formed on a periphery of the active space 22. The active space 22 and the passive space 20 are both shaped as rotationally symmetric spaces or chambers, whereby they are rotationally symmetric around an axis A defines by the motor shaft (not shown in figure 3). In the gap 18 or close to the gap 18 a capillary mechanism 36 is embedded. In the illustration shown in figure 3, the capillary mechanism 36 is arranged in the gap 18 and formed as a continuously decreasing width of the gap 18 towards the hole 28. The width of the gap 18 may decrease from. point e to point b, as illustrated in figure 3, from O.7mm to O.2mm. Alternatively it may decrease from point e from any of 1mm, O.9mm, O.8mm, O.7mm, O.6mm to any of O.5mm, O.4mm, O.3mm, O.2mm or even O.1mm at point b. By designing the gap 18 in such a manner, the capillary effect on the oil is stronger the closer the liquid or oil travels to towards the hole 28. Thus the capillary force acting on the liquid is always directed towards the hole 28. The liquid is thus always staying within the gap 18 and therewith air cannot enter the active spaceTurning now to figure 4, which illustrates another solution for a capillary mechanism 36' in the form of a wick structure 38. The wick structure 38 is shaped so that it snuggly fits into the gap l8 (c.f. figure 3), and therewith as a lateral surface of a cut cone. The wick structure 38 may be made of a perforated metal, such aluminium, steel or titan or a fabric such as cotton, glass fibre, carbon fibre or any other suitable material or a combination thereof. The wick structure 38 has the same effect, the hole 28 so namely to draw liquid via capillary effect towards that the active chamber 22 is always filled with liquid and so that not air or air bubbles can enter it. Due to the presence of air in the passive space 20, the capillary force will always act towards the hole 28 and the active space 22, respectively. The capillary force is not strong enough to act in the other direction since the active space 22 is always filled with oil or liquid.

The wick structure 38 is configured to be embedded in the gap ll8, l8 of a prior art hydraulic power tool 100 or in the gap l8 of a hydraulic power tool having a coupling mechanism laccording to figure Figure 5 illustrates a coupling mechanism l0' with the wick structure 38 embedded in the gap l8'. The gap l8' has thereby a similar shape as the one illustrated in figure 2 and therewith a constant width between 0.5mm to l.5mm. Again the wick structure 38 may also be embedded in the embodiment of figure 3, thus in a gap l8 with continuously decreasing width D.

Figure 6 illustrates still another capillary mechanism 36" also in the form of a wick structure 38' 38' whereby the wick structure comprises a projection 42 or extension configured to extend into the passive space 20 and all the way to the bottom 40 of the active space (c.f. 38' is figure 5) in order to ensure that the wick structure always saturated with liquid or oil.

Figures 3 and 5 illustrates the hydraulic coupling mechanism , 10' in different orientations, figure 3 angled and figure 5 upside down, 36, 36', 36" this is to show that the capillary mechanism described herein always provides oil to the no matter the hole 28 and the active space 22, respectively, orientation of the hydraulic power tool. 38' When the wick structure 38, is designed to be embedded in the gap 18 according to figure 3, then its thickness may be adapted accordingly so that it corresponds to the decreasing width D of the gap 18 and so that it snuggly fits into the gap The invention has now been described with reference to the enclosed figures. Various combinations are herewith enclosed in the invention. Different features from different embodiments may be combined in order to further improve the functioning and reliability of the hydraulic power tool. In the example the hydraulic power tool may be a battery driven power tool. It is however also conceivable to apply the solution to a cable driven power tool or even an air pressure driven power tool.

Claims

1. Claims A hydraulic power tool for tightening by applying torque pulses to a fastener, the hydraulic power tool comprising a hydraulic coupling mechanism (110, 10, 10') and a motor (108) with a motor shaft 132), the hydraulic coupling mechanism (110, 10, 10') comprising: a first part (116, 16) comprising a passive space (120, 20) and a cylinder (130, 30) with at least one projection (124), the cylinder (130, 30) being configured to be driven by the motor shaft (132); a second part (114, 14) comprising an anvil configured to be coupled to the fastener for applying torque pulses to the fastener, an active space (122, 22), at least one hole (28) (122, 22), arranged at a periphery of the active space at least one movable engaging element (126) (124) of (126) and for engagement with the at least one projection the cylinder (130, 30), the engaging elements the at least one projection (124) being arranged in the active space (122); a gap (118, 18, 18') arranged between the first part (116, 16) and the second part (114, 14) interconnecting the passive space (120, 20) and the active space (122, 22) via the at least one hole (28), wherein the active space (122, 22) (120, 20) is filled with oil and the passive space is filled with oil and air, said hydraulic power tool being characterized by comprising a capillary mechanism (36, 36', 36") arranged in the gap (118, 18, 18'), said capillary mechanism (36, 36', 36") keeping the oil in the gap (118, 18, 18') using capillary force so that the active space (122, 22) is in any circumstance filled with oil.

2. The hydraulic power tool according to claim 1, wherein the capillary mechanism (36, 36', 36") is configured to draw the oil via capillary force in the direction of the hole (28) and the active space (122, 22), respectively.

3. The hydraulic power tool according to any of the (118, 18, 18') is defined. by the previous claims, wherein the gap rotationally' symmetric around. an axis motor shaft andat least partially shaped like a lateral surface of a cone or cut cone.

4. The hydraulic power tool according to any of the previous claims, wherein the pressure in the active space (122, 22) is higher than the pressure in the passive space (120, 20).

5. The hydraulic power tool according to any of the previous claims, wherein the capillary mechanism (36', 36") is a wick structure (38, 38') that is shaped according to the gap (118, 18, 18') so that it can be placed snug in the gap (118, 18, 18') configured to draw oil towards the active space (122, 22).

6. The hydraulic power tool according to claim 5, wherein the wick structure (38, 38') is at least partially shaped like a lateral surface of a cone.

7. The hydraulic power tool according to clamn 5 or 6, (38') that reaches to a bottom (40) wherein. the wick structure further comprises a projection (42) of the passive space (20) so that the wick structure is always saturated with oil.

8. The hydraulic power tool according to any of claimsto 7, wherein the wick structure (38, 38') is made of Ümetal, such as jperforated nætal in order 11) generate capillary force.

9. The hydraulic power tool according to claim 8, wherein the metal is aluminum.

10. power tool according to any of claims(38, 38') The hydraulic to 7, wherein the wick structure is made of fabric such as cotton, glass fiber, carbon fibre or any other suitable fiber material or a combination thereof.

11.The hydraulic power tool according to any of claims 1 to 4, wherein the capillary mechanism (36) is a continuously decreasing width (D) in the gap (18) towards the hole (28).

12.The hydraulic power tool according to claim 11, wherein width in the gap (18) is chosen to be 0.6mm to 1mm at a first end (e) of the gap (18) close to the passive space and 0.5mm to 0.1mm at a second end (b) of the gap (22), (20) close the active space preferably 0.6 to 0.8mm at the first end (e) and 0.3 to 0.1mm at the second end (b). A wick structure (38, 38') being designed to be arranged in a gap (118, 18, 18') of a hydraulic power tool 5-according' to any' of claims (C, wherein. said. wick structure comprises a wick element that can draw a liquid wherein said wick structure (38, 38') is shaped according to the gap (118, 18, 18') (118, 18, 18') using capillary force, so that it can be placed snug in the gap and wherein said wick structure is configured to draw oil towards the active space (122, 22).