Device for Tensioning a Screw

Abstract

The present invention pertains to a device for tensioning a screw, containing a screw pulling member comprising an engagement section for engagement with a thread of a screw to be tensioned, wherein a toggle lever mechanism for displacing the screw pulling member relative to a part to be tightened.

Claims

1. A device for tensioning a screw, containing: a screw pulling member comprising an engagement section for engagement with a thread of a screw to be tensioned, and a toggle lever mechanism for displacing the screw pulling member relative to a part to be tightened.

2. The device according to claim 1, further comprising a support member for supporting the toggle lever mechanism against the part to be tightened.

3. The device according to claim 2, wherein the toggle lever mechanism comprises a first lever member and a second lever member, wherein the first lever member is at a first side pivotably connected with the support member and at a second side pivotably connected with a second side of the second lever member, and the second lever member is pivotably connected with the screw pulling member at a first side of the second lever member.

4. The device according to claim 3, wherein the first lever member is pivotable relative to the support member about a first pivot axis and pivotable relative the second lever member about a second pivot axis, and the second member is pivotable relative to the screw pulling member about a third pivot axis, wherein preferably the first, second and third pivot axis are aligned parallel to each other.

5. The device according to claim L further comprising a guide for guiding the screw pulling member in direction of a pulling axis defined by the guide.

6. The device according to claim 1, wherein the toggle lever mechanism comprises an actuator unit, wherein the actuator unit is configured to define a position of the first lever member and/or the second lever member.

7. The device according to claim 6, wherein the actuator unit is a lever arm rigidly connected to the first lever member or the second lever member.

8. The device according to claim 6, wherein the actuator unit comprises an actuator screw, preferably a jackscrew, in engagement with an engagement member, wherein the actuator unit is configured so that a rotation of the actuator screw causes pivoting of the first lever member and/or the second lever member.

9. The device according to claim 8, wherein the engagement member is arranged at the first lever member, the second lever member or a connection member pivotably connecting the first lever member and the second lever member, wherein preferably the actuator screw is rotatably supported at a guide and/or the support member.

10. The Device according to claim 8, wherein the actuator screw is rotatably supported at the first lever member, the second lever member or a connection member pivotably connecting the first lever member and the second lever member, wherein preferably the engagement member is arranged at the guide and/or the support member.

11. The device according to claim 3, wherein the support member and the first lever member comprise complementarily formed, arc-shaped contact surfaces forming a pivot hinge for enabling pivoting of the first lever member about the support member and/or wherein the first lever member and the second lever member comprise complementarily formed, arc-shaped contact surfaces forming a pivot hinge for enabling pivoting of the first lever member and the second lever member relative to each other, and/or wherein the screw pulling member and the second lever member comprise complementarily formed, arc-shaped contact surfaces forming a pivot hinge for enabling pivoting, of the second lever member about the screw pulling member.

12. The device according to claim 3, wherein the support member and the first lever member are connected via a bolt connection, and/or wherein the first lever member and the second lever member are connected via a bolt connection, and/or wherein the screw pulling member and the second lever member are connected via a bolt connection.

13. The device according to claim 11, wherein a contact, area of the contact surfaces or a contact area of the bolt connections is at least double the size of a cross section of a screw for which the engagement section is configured to engage with, and/or the contact surfaces or the surfaces of the parts forming the bolt connections comprise a friction-reducing coating.

14. The device according to claim 3, wherein the toggle lever mechanism comprises two pairs of first and second lever members, wherein the two pairs are arranged on opposite sides with respect to the engagement section.

15. The device according to claim 14, wherein the actuator screw, is supported on both pairs, wherein preferably the actuator screw is rotatably supported at the first pair and the second pair comprises the engagement member, or the actuator screw is rotatably supported at the second pair and the first pair comprises the engagement member, or both pairs each comprise an engagement member, wherein the actuator screw comprises a first threaded section engaging with, the engagement member of the first pair and a second threaded section having a pitch opposite to the pitch of the first threaded section engaging with the engagement member of the second pair.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present disclosure will be more readily appreciated by reference to the following detailed description when being considered in connection with the accompanying drawings in which:

[0009] FIG. 1 is a schematic perspective side view of a device for tensioning a screw according to a first embodiment;

[0010] FIG. 2 is a schematic exploded view of the device of FIG. 1;

[0011] FIG. 3 is a schematic sectional view through the device shown in FIG. 1 along its longitudinal axis.

[0012] FIG. 4 is another schematic perspective side view of the device of FIG. 1;

[0013] FIG. 5 is a schematic sectional view through the device shown in FIG. 4 along its longitudinal axis.

[0014] FIG. 6 is another schematic sectional view through the device shown in FIG. 1 along its longitudinal axis.

[0015] FIG. 7 is a schematic perspective side view of a device for tensioning a screw according to a second embodiment;

[0016] FIG. 8 is a schematic perspective side view of a device for tensioning a screw according to a third embodiment; and

[0017] FIG. 9 is a schematic perspective side view of a device for tensioning a screw according to a forth embodiment;

[0018] FIGS. 10A and 10B depict parallelograms of forces of the toggle lever mechanism of the device according to FIGS. 7 to 9 in a first and a second position of the lever members of the toggle lever mechanism.

[0019] FIG. 11 depict a diagram of a force of an actuator screw over a tension in a corresponding screw to be tensioned.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0020] In the following, the invention will be explained in more detail with reference to the accompanying Figures. In the Figures, like elements are denoted by identical reference numerals and repeated description thereof may be omitted in order to avoid redundancies.

[0021] In FIG. 1, a schematic perspective side view of a device 1 for tensioning a screw for use of tightening a part to be tightened 5 according to a first embodiment is shown. The device 1 comprises a cylinder-shaped guide 7 substantiality encasing a toggle lever mechanism 4 which is coupled to the guide 7 via an actuator unit 8. The device 1 and its components are described in detail below.

[0022] FIG. 2 shows a schematic exploded view of the device of FIG. 1. As described above, the device 1 comprises the guide 7. Moreover, the device 1 comprises a screw pulling member 2 having an engagement section 20 for engagement with a thread of a screw 3 to be tightened. The screw pulling member 2 is displaced with respect to a part to be tightened 5 via the toggle lever mechanism 4.

[0023] The toggle lever mechanism 4 comprises a first lever member 40 and a second lever member 41, an engagement member 81 which engages with an actuator screw 80 of the actuator unit 8, and a support pin 84 which engages with the actuator screw 80 and which is supported against the guide 7. Furthermore, the device 1 comprises an optional distance piece 9 which is to be placed around a nut 30 of the screw 3.

[0024] As can be also seen in FIG. 3, the screw pulling member 2 comprises guiding areas 22 with which the screw pulling member 2 can slide over an inner circumferential wall of the guide 7.

[0025] FIG. 3 shows a schematic sectional view through the device 1 shown in FIG. 1 along its longitudinal axis A. The first lever member 40 is at a first side pivotably connected with a support member 6 and at a second side pivotably connected with a second side of the second lever member 41, and the second member 40 is pivotably connected with the screw pulling member 2 at a first side of the second lever member 41. Thus, the first lever member 40 is pivotable relative to the support member 6 about a first pivot axis 42 and pivotable relative the second lever member 41 about a second pivot axis 43, and the second lever member 41 is furthermore pivotable relative to the screw pulling member 2 about a third pivot axis 44, wherein the first, second and third pivot axes 42, 43, 44 are aligned parallel to each other.

[0026] The engagement member 81 is rotatably supported in the first lever member 40. The support pin 84 is rotatably supported at the guide 7. The actuator screw 80 engages with the engagement member 81 with a thread of the actuator screw 80 and is supported against the support pin 84 in the longitudinal direction of the screw 80 via its head 85. Both the engagement member 81 and the support pin 84 are rotatably supported perpendicular to the longitudinal axis of the actuator screw 80.

[0027] The support member 6 supports the toggle lever mechanism 4 against the part to be tightened 5, wherein in this embodiment the distance piece 9 is arranged between the support member 6 and the part to be tightened 5. As can be seen with regard to the pivot axes 42, 43, 44, the toggle lever mechanism 4 is in a pivoted state in which the second pivot axis 43 is spaced apart with the distance D from the longitudinal axis A of the device 1, which, in this embodiment, at the same time is the longitudinal axis of the screw 3 to be tensioned and the pulling direction. Both, the first pivot axis 42 and the third pivot axis 44 intersect with the longitudinal axis A.

[0028] FIG. 3 shows the device 1 in a position before tensioning the screw 3. That is, the screw pulling member 2 is engaged with the screw 3 via its engagement section 20. In this state, there is no tension on the toggle lever mechanism 4.

[0029] The contact areas of the contact surfaces 46 between the support member 6 and the first lever member 40, the first lever member 40 and the second lever member 41, and the second lever member 41 and the screw pulling member 2 are each at least double the size of a cross section of the screw 3. Furthermore, the contact surfaces 46 each comprise a friction-reducing coating.

[0030] FIG. 4 shows another schematic perspective side view of the device 1 of FIG. 1, wherein the guide 7 is not shown. In this view, the toggle lever mechanism 4 is in an elongated position in which the screw 3 is tightened via the screw pulling member 2.

[0031] In FIG. 5, a schematic sectional view through the device 1 shown in FIG. 4 along its longitudinal axis A is depicted. In this position of the toggle lever mechanism 4, the three pivot axes 42, 43, 44 each intersect with the longitudinal axis A. By bringing the second pivot axis 43 in line with the other pivot axes 42, 44, the screw pulling member 2 is displaced in direction of the longitudinal axis A away from the part to be tightened 5, which results in tensioning of the screw 3 in correlation with the elongation L by which the screw 3 is elongated via the displacement of the screw pulling member 2 as described above.

[0032] FIG. 6 shows another schematic sectional view through the device 1 shown in FIG. 1 along its longitudinal axis A perpendicular to the sectional view of FIG. 3. In this view, it can be clearly seen that the screw pulling member 2 is supported against the second lever member 41 on a top side of the device 1, extends down on both sides of the toggle lever mechanism 4 and ends in the engagement section 20.

[0033] In the following, the functioning of the mechanical force multiplying tensioning device 1 according to the first embodiment is described. In the first step, the nut 30 is screwed onto the screw 3, until it rests on a surface of the part to be tightened 5. Afterwards the distance piece 9 is placed around the nut 30 and onto the part to be tightened 5. Then, the device 1 is placed above the screw and the screw pulling member 2 is brought in engagement with a thread of the screw 3 by rotation of the device 1 about its longitudinal axis A, resulting in a setup as shown in FIG. 3.

[0034] In a next step, the actuator screw 80 is turned until a predetermined starting tension force is applied onto the screw 3. Determination of the tension force applied on the screw 3 via the device 1 can be achieved by e.g. measuring the stress in the support member 6, e.g. by attaching one or more strain gauges on to the support member 6, by which, after an initial calibration, the force, stress and elongation of the screw 3 can be calculated. Alternatively, other ways of detecting stress, elongation etc. of at least one of the parts of the device 1 can be applied. Detecting stresses or elongation is per se well known. After the starting tension force is reached, the nut 30 is rotated until it makes contact with the surface of the parts to be tightened 5. Thereby, a predetermined starting point is achieved.

[0035] In a further step, the actuator screw 80 is further rotated until a second tension force on the screw 3 is reached. After that, the nut 30 is rotated about a predetermined amount of rotations, whereby the nut 30 is displaced towards the part to be tightened 5 about a predetermined distance.

[0036] Rotation of the nut 30 is achieved by placing a key (not shown) through a window or notches (not shown) in the guide 7. The latter is known, e.g. from SU 929429 A1.

[0037] After rotation of the nut 30, the actuator screw 80 is released and the device 1 is removed. The screw 3 now comprises a predetermined tension, and thus the screw connection is tightened with a predetermined stress level.

[0038] FIG. 7 shows a schematic side view of a device 1 for tensioning a screw according to a second embodiment. The device 1 in this embodiment substantially comprises the same structure as the device 1 according to the first embodiment. Unlike the device 1 according to the first embodiment, the device 1 according to the second embodiment comprises two pairs 47, 48 of first and second lever members 40, 41, wherein the two pairs 47, 48 are arranged on opposite sides with respect to the engagement section 20. Both pairs 47, 48 each comprise an engagement member 81 provided in form of a connection member 45 which connects the first lever member 40 and the second lever member 41. The actuator screw 80 has the form of a jackscrew and comprises a first threaded section 87 engaging with the engagement member 81 of the first pair 47 and a second threaded section 88 having a pitch opposite to the pitch of the first threaded section 87 and engaging with the engagement member 81 of the second pair 48. Furthermore, the support member 6 is in direct contact with the part to be tightened 5.

[0039] For rotating the actuator screw 80, a lever 86 is attached to the screw 80. The lever 86 may further comprise a torque measuring device (not shown) which is per se known.

[0040] Due to provision of the connection member 45, the second pivot axis 43 is split into two second pivot axes 43 and 43.

[0041] By rotating the actuator screw 80 in a clockwise direction, the connection members 45 are displaced towards each other, which results in a displacement of the screw pulling member 2 along the longitudinal axis A away from the parts to be tightened 5. Thereby, the screw 3 can be tensioned as described with respect to the first embodiment.

[0042] FIG. 8 shows a schematic side view of a device 1 for tensioning a screw 3 according to a third embodiment. The device 1 is substantially similar to the device shown in FIG. 7, wherein the actuator screw 80 merely comprises the first threaded section 87. At the second pair 48, the actuator screw 80 is rotatably supported against the connection member 45 of the second pair 48. In this regard, the screw 80 comprises a shoulder 82 and a retaining ring 83. The actuator screw 80 is held rotatably about its longitudinal axis in the connection member 45. The shoulder 82 and the retaining ring 83 prevent displacement of the actuator screw 80 along its longitudinal axis.

[0043] Furthermore, the actuator screw 80 comprises a head 85 with a hexagon socket (not shown).

[0044] FIG. 9 shows a schematic side view of a device 1 for tensioning a screw according to a forth embodiment. The device 1 is substantially the same as the device shown in FIG. 8, wherein in addition, a guide 7 is provided in which the screw pulling member 2 is guided in the longitudinal direction A of the device 1 via its guiding areas 22.

[0045] FIGS. 10A and 10B depict parallelograms of forces of the toggle lever mechanism 4 of the devices shown in FIGS. 7 to 9 in a first and a second position of the lever members 40, 41 of the toggle lever mechanism 4. FIG. 10A shows the kinematics of the device 1 as shown in FIGS. 7 to 9. With reference signs a40 and a41, the function lines of the first lever member 40 and the second lever member 41 are depicted. The Force Fas is the force applied by the actuator screw. The force Ft is the component of the force transmitted via the first and second lever member 41, 41 which causes tensioning of the screw 3.

[0046] FIG. 10B shows another parallelogram of forces, wherein the pairs 47,48 of the toggle lever mechanism 4 are in an elongated position with respect to the position shown in FIG. 10A. With other words the angle between the longitudinal direction A and the function line a40 of the first lever member 40 in FIG. 10A is bigger than the angle in FIG. 10B. The amount of the force Fas is equal in in FIGS. 10A and 10B. As can be seen, the resulting tension force Ft in FIG. 10B is significantly larger than the resulting tension force Ft as depicted in FIG. 10A. Hence, with decreasing angle , the tension force Ft increases when applying a constant force Fas.

[0047] FIG. 11 depicts a diagram of a force Fas of an actuator screw over a tension T in a corresponding screw to be tensioned. With the reference signs W the distribution of force of an actuator screw of a device for tensioning a screw having a wedge mechanism is depicted, and with the reference sign TL the distribution of force of the actuator screw 80 according to a device having a toggle lever mechanism is depicted. As can be seen, with increasing tension T the force and hence the stress of a actuator screw in a wedge mechanism raises significantly higher than the force and stress of a actuator screw 80 for a toggle lever mechanism 4 according to the invention.

[0048] It will be obvious for a person skilled in the art that these embodiments and items only depict examples of a plurality of possibilities. Hence, the embodiments shown here should not be understood to form a limitation of these features and configurations. Any possible combination and configuration of the described features can be chosen according to the scope of the invention.

[0049] This is particular the case with respect to the following optional features which may be combined with some or all embodiments, items and/or features mentioned before in any technically feasible combination.

[0050] A device for tensioning a screw may be provided, which may contain a screw pulling member comprising an engagement section for engagement with a thread of a screw to be tensioned and further containing a toggle lever mechanism for displacing the screw pulling member relative to a part to be tightened.

[0051] It has been found that by means a toggle lever mechanism for displacing the screw pulling member relative to a part to be tightened, using a hydraulic fluid which could become compressed may not be necessary any more. Furthermore, by the toggle lever mechanism, a force/stroke conversion may be provided which may differ with the position orientation of the toggle lever mechanism. In other words, the ratio of the resulting force applied on the screw to be tensioned by the screw pulling member via the toggle lever mechanism and the force applied on the toggle lever mechanism for generating the above-mentioned resulting force may raise with decreasing pitch of the toggle lever mechanism with respect to a longitudinal axis of the screw to tensioned. A possible consequence may be that also big screws, e.g. M35, M36 or even M40 could be tensioned to the required extent by a relatively small force applied upon the toggle lever mechanism. In addition, by means of the toggle lever mechanism, the tension on the screw may be set relatively exact, which could be advantageous for e.g. screws tightening a piston rod or a cylinder head of a stationary gas combustion engine.

[0052] Moreover, also for tensioning and subsequently tightening big and very big screws up to M40 and bigger, there may be no need for providing a hydraulic system. Thus, user safety may be significantly increased. The device according to the embodiment above furthermore may facilitate service and maintenance of e.g. gas combustion engines in the field, as the necessity of setting up a whole hydraulic system for tensioning the screws of the engine may be eliminated. As a possible consequence, also the necessary man hours and thus the operating costs may be decreased significantly, as merely a single operator may be able to operate the device and a second worker operating the high-pressure pump may not be needed anymore.

[0053] It might be advantageous to provide save and rigid support of the toggle lever mechanism against the part to be tightened. In this regard, according to an aspect, the device further may comprise a support member for supporting the toggle lever mechanism against the part to be tightened.

[0054] According to another aspect, the toggle lever mechanism may comprise a first lever member and a second lever member, wherein the first lever member may be at a first side pivotably connected with the support member and at a second side pivotably connected with a second side of the second lever member, and the second member may be pivotably connected with the screw pulling member at a first side of the second lever member. By this structure, an exponentially increasing force/stroke conversion ratio may be provided. That is, with increasing angle enclosed by the first lever member and the second lever member, thus the angle between the longitudinal axis of the screw and the first lever member and second lever member, respectively, the multiplication of force applied via the toggle lever mechanism may be increased due to its changing kinematics.

[0055] A very accurate force multiplication may be achieved, when according to another aspect, the first lever member may be pivotable relative to the support member about a first pivot axis and pivotable relative the second lever member about a second pivot axis, and the second member may be pivotable relative to the screw pulling member about a third pivot axis, wherein preferably the first, second and third pivot axis could be aligned parallel to each other.

[0056] As it could be advantageous to further increase the accuracy of the device, according to another aspect, the device further may comprise a guide for guiding the screw pulling member in direction of a pulling axis defined by the guide. The pulling axis may correspond to the longitudinal axis of the screw to be tensioned.

[0057] In another aspect, the toggle lever mechanism may comprise an actuator unit, wherein the actuator unit may be configured to define a position of the first lever member and/or the second lever member. Thereby, among others, the amount of tensioning, with other words the elongation of the screw can be set very accurate by means of the actuator unit.

[0058] When the actuator unit may be a lever arm rigidly connected to the first lever member or the second lever member, an operator for instance merely would have to apply a relatively small force onto the lever arm for creating a tensioning force via the screw pulling member onto the screw to be tensioned.

[0059] In another aspect, the actuator unit may comprise an actuator screw, preferably a jackscrew, in engagement with an engagement member, wherein the actuator unit may be configured so that a rotation of the actuator screw causes pivoting of the first lever member and/or the second lever member. Thereby, for instance, the tensioning force can be applied very accurate as it may be in direct relation with the torque and the angle of rotation, respectively, applied onto the actuator screw.

[0060] Among others, a very simple, compact and at the same time rigid structure could be accomplished when according to another aspect, the engagement member may be arranged at the first lever member, the second lever member or a connection member pivotably connecting the first lever member and the second lever member, wherein preferably the actuator screw may be rotatably supported at the guide and/or the support member.

[0061] Alternatively, the actuator screw may be rotatably supported at the first lever member, the second lever member or a connection member pivotably connecting the first lever member and the second lever member, wherein the engagement member may be arranged at the guide and/or the support member.

[0062] For instance a particularly rigid and compact structure of the device could be attained when the support member and the first lever member may comprise complementarily formed, arc-shaped contact surfaces forming a pivot hinge for enabling pivoting of the first lever member about the support member and/or wherein the first lever member and the second lever member may comprise complementarily formed, arc-shaped contact surfaces forming a pivot hinge for enabling pivoting of the first lever member and the second lever member relative to each other, and/or wherein the screw pulling member and the second lever member may comprise complementarily formed, arc-shaped contact surfaces forming a pivot hinge for enabling pivoting of the second lever member about the screw pulling member.

[0063] According to another aspect, the support member and the first lever member may be connected via a bolt connection, and/or wherein the first lever member and the second lever member may be connected via a bolt connection, and/or wherein the screw pulling member and the second lever member may be connected via a bolt connection. Bolt connections are per se well known and thus easily to design and form.

[0064] Among others for ensuring persistence of the device and/or avoiding damages due to excessively high compressive stress in the parts of the device, according to another aspect, a contact area of the contact surfaces or a contact area of the bolt connections may be at least double the size of a cross section of a screw for which the engagement section is configured to engage with.

[0065] When the contact surfaces or the surfaces of the parts forming the bolt connections may comprise a friction-reducing coating, wear and damages due to friction could be significantly reduced or even substantially avoided.

[0066] According to another aspect, the toggle lever mechanism may comprise two pairs of first and second lever members, wherein the two pairs may be arranged on opposite sides with respect to the engagement section. Thereby, a force on the device lateral to the pulling direction and tensioning direction, respectively, could potentially be minimized or even completely avoided, as the directions of the lateral forces acting on the first pair and the second pair may oppose each other and, as a result, may compensate each other. An accordingly designed device, thus, could comprise a very simple structure.

[0067] According to another aspect, the actuator screw may be supported on both pairs, wherein preferably the actuator screw may be rotatably supported at the first pair and the second pair may comprise the engagement member, or the actuator screw may be rotatably supported at the second pair and the first pair may comprise the engagement member, or both pairs each may comprise an engagement member, wherein the actuator screw may comprise a first threaded section engaging with the engagement member of the first pair and a second threaded section having a pitch opposite to the pitch of the first threaded section engaging with the engagement member of the second pair. Thereby, the pairs and the actuator screw also may have the function of a guide for the screw pulling member.

[0068] According to another aspect, the toggle lever mechanism may be arranged on a side of the support member facing away from a contact part of the support member making contact with the part to be tightened. This may lead to a very simple and rigid structure of the device.

INDUSTRIAL APPLICABILITY

[0069] With reference to the Figures, a device 1 for tensioning a screw 3 is suggested, containing a screw pulling member 2 comprising an engagement section 20 for engagement with a thread of a screw 3 to be tensioned, and a toggle lever mechanism 4 for displacing the screw pulling member 2 relative to a part to be tightened 5.

[0070] The device 1 as mentioned above is applicable for tightening screws, in particular for tightening large screws, for instance bigger than M20 screws. The device can be engaged with a thread of a screw to be tightened, and then, the toggle lever mechanism can be operated such that the screw pulling member tensions the screw. Afterwards, a nut engaging with the thread of the screw can be rotated towards a part to be tightened. After loosening the toggle lever, a tightened screw connection is provided. The device as mentioned above is in particular applicable for tightening screws tightening a piston rod or a cylinder head of a stationary gas combustion engine.

[0071] Hence, using a hydraulic fluid which could become compressed is not necessary for tensioning a screw to be tightened any more. Also, service and maintenance of e.g. gas combustion engines in the field can be facilitated, as the necessity of setting up a whole hydraulic system for tensioning the screws of the engine may be eliminated.