HYDRAULIC TORQUE IMPULSE TOOL

Abstract: A hydraulic torque impulse tool, comprising an inertia drive member (10) which is rotated by a motor and which includes a fluid chamber (19), and a seal and torque transmitting mechanism (30) which is arranged to divide the fluid chamber (19) into two compartments (38, 39) during a short interval of the relative rotation between the drive member (19) and the output spindle (11). An annular leaf spring valve (82) is arranged to control the flow through a bypass passage (70,81, 79) interconnecting the two fluid chamber compartments (38, 39). The leaf spring valve (82) which by its shape is pretensioned toward open condition automatically occupies the open condition as the difference in pressure between the fluid chamber compartments (39, 39) is low and a closed condition as this difference exceeds a certain level.

Description: This invention relates to a hydraulic torque impulse tool, primarily intended for tightening and loosening threaded joints such as screws, bolts, nuts etc. In particular, the invention concerns a hydraulic torque impulse tool comprising a tool housing, an inertia drive member coupled to a rotation motor in said housing and including a fluid chamber, an output spindle having an impulse receiving rear portion extending into said fluid chamber, an impulse generating seal means movably arranged in said fluid chamber and dividing the latter into a high pressure compartment and a low pressure compartment during a limited portion of its movement relative to said fluid chamber, a fluid passage means extending past said seal means, and a pressure responsive valve means arranged to control the flow through said passage means by shifting automatically from an open condition to a closed condition as the difference in pressure between said high pressure compartment and said low pressure compartment exceeds a certain level. A hydraulic torque impulse tool of this type is previously described in US Patent No 3,283,537. In this prior art tool the impulse generating seal means comprises a vane which is slidably supported in a radial slot in the rear portion of the output spindle and two diametrically opposite lands in the fluid chamber for simultaneous cooperation with the vane and the spindle itself such that once each revolution of the relative rotation between the inertia drive member and the output spindle the fluid chamber is divided into a high pressure compartment and a low pressure compartment. Past this seal means there is a fluid passage and a spring biased valve. In this patent there are shown two alternative fluid passage locations, one in the inertia drive member (Figs 2 and 5) and another in the output spindle (Fig 6). In both cases the fluid passage and valve are arranged to permit a bypass flow between the two fluid chamber compartments as the pressure difference between these compartments is below a certain level and to prevent such flow as the pressure difference exceeds that level. This means that the valve is shut at a high relative rotation speed between the drive member and the output spindle such that a high pressure impulse may be accomplished. It also means that at low relative rotation speed between the drive member and the output spindle the valve is kept open. The purpose of this valve controlled bypass is to avoid a pressure build-up at low relative rotation speed. This occurs after delivery of each high pressure torque impulse when the drive member is abruptly stopped while the seal means is still effective in preventing fluid flow between the fluid chamber compartments. Without the provision of the valve controlled bypass passage, the acceleration of the drive member on the next impulse generating cycle would not commence until the engagement interval of the seal means had been passed and the hydraulic braking of the drive member had ceased. Such pressure build-up at low speed relative rotation between the drive member and the output spindle is undesirable since it extends the cycle time and, thereby, keeps down the impulse rate and output torque capacity of the tool. The type of valve disclosed in the above patent, however, is disadvantageous in that it has a small flow capacity in relation to its dimensions and includes a helical bias spring which in this application has a limited service life due to its insufficient fatigue strength. The reason is that the high impulse generating pressure peaks are build up almost instantaneously and make the valve accelerate very rapidly. Accordingly the dynamic stresses to which the spring is exposed are severe. The main object of the present invention is to assomplish a hydraulic torque impulse tool of the above type including an improved byp ass control valve which has a large flow capacity and which is apt to withstand the dynamic stresses caused by the high impulse generating pressure peaks in the fluid chamber. Further advantages and significant features of the invention will be apparent from the following description and drawings. In the drawings Fig 1 shows a longitudinal section through a pivoting piston type torque impulse tool provided with a valve controlled bypass according to the invention. Figs 2 to 5 show cross sections taken along line II-II in Fig 1, which illustrate different sequential positions of the torque impulse generating parts. Fig 6 shows a side view of the piston incorporated in the tool shown in Figs 1 to 5. Fig 7 shows a cross section taken along line VII-VII in Fig 1. Fig 8 shows a cross section along line VIII-VIII in Fig 1 showing the bypass control valve according to the invention. Fig 9 shows a fragmental section of the tool in Fig 1 and is indicated by line IX-IX in Fig 8. A complete torque impulse delivering tool consists not only of the hydraulic impulse mechanism, embodiments of which are illustrated in the drawing figures, but comprises a tool housing, tool support means, a rotation motor and power supply means. Since these details do not form any part of the invention and are not intimately related to the specific features of the impulse mechanism, the drawings have been limited to the impulse mechanism only. The hydraulic impulse mechanism shown in the drawing figures comprises an inertia drive member 10 which is rotatably supported on an output spindle 11 which in turn is rotatably journalled in the tool housing 12. A bearing sleeve 13 mounted in the forward end portion 14 of the tool housing 12 forms the output spindle bearing. At its forward end, the output spindle 11 is formed with a square drive portion 15 on which a nut or screw engaging socket is attachable. The inertia drive member 10 is axially locked relative to the output spindle 11 by means of steel balls 16 running in circumferential grooves in the spindle 11 and the inertia drive member 10. The inertia drive member 10 is mainly cylindrical in shape and comprises a cup-shaped main body 18 enclosing a concentric hydraulic fluid chamber 19. At its forward end, the fluid chamber 19 is closed by a separate end closure 20 which is locked in position by a ring nut 21 engaging internal threads 22 on the main body 18. At its rear end the body 18 is formed with a splined socket portion 23 in which the splined shaft 24 of the rotation motor (not shown) of the tool is received. One of the motor shaft bearings 25 serves as a bearing for the inertia drive member 10 as well. Within the hydraulic fluid chamber 19, there are mounted two cylindrical pins 27, 28 which are parallel to each other as well as to the rotation axis of the inertia drive member 10. These pins 27, 28 are located diametrically opposite each other and are both partly received in longitudinal grooves in the chamber wall. (See Figs 2-5). Both pins 27, 28 also extend into the forward end closure 20, thereby positively locking the latter to the main body 18 as regards rotation. One of the pins 27 serves as a fulcrum for a pivoting piston 30, whereas the other pin 28 forms a seal and guide means for cooperation with a seal portion 31 and two guide flanges 32, 33 on the piston 30. The piston 30 is formed with flat end surfaces 34, 35 for sealing cooperation with opposite flat end walls 36, 37 of the hydraulic fluid chamber 19. The latter is divided by the piston 30 into two compartments 38, 39. The piston 30 is formed with a central opening 40 through which the rear end portion of the output spindle 11 extends. The edge contour of this opening 40 forms two sets of cam surfaces which are arranged to engage selectively two separate cam surfaces on the output spindle 11. There are provided two separate sets of cam surfaces on each one of the output spindle 11 and the piston 30 for the purpose of making the tool operable in both directions. However, one set of cam means only on each one of the output spindle 11 and the piston 30 is active to accomplish the intended engagement between the spindle 11 and the piston 30 when operating the tool in one direction. For a normal clockwise rotation of the inertia drive member 10 relative to the output spindle 11 (see arrows in Figs 2-5), an abruptly inclined cam surface 42 on the output spindle 11 is engaged alternatingly by a likewise abruptly inclined cam surface 43 and a gradually sloping cam surface 44 on the piston 30. The cam surface inclinations are here related to the directions of thought circle tangents in each point of the cam profile. By interengagement of the cam means on the output spindle 11 and the piston 30, the latter is caused to perform a reciprocative pivoting movement in the fluid chamber 19. A certain stroke length is thereby obtained. For accomplishing a pivoting movement of the piston 30 also when the inertia drive member 10 is rotated in the anti-clockwise direction, another abruptly inclined cam surface 42¹ on the output spindle 11 is engaged alternatingly by an abruptly inclined cam surface 43¹ and a gradually sloping cam surface 44¹ on the piston 30. In the shown embodiments of the invention the cooperating cam means are symmetrically designed so as to generate the same piston operation characteristics in both directions of rotation. For the purpose of absorbing changes in the hydraulic fluid volume due to temperature variations, an annular expansion chamber 45 is provided in the rear end closure 20. This expansion chamber 45 communicates with the fluid chamber 19 and is filled with a foamed plastic material. The foamed plastic material is of the closed cell type and is acted upon directly by the hydraulic fluid. In the inertia drive member 10 there is provided an output torque limiting device 50. See Fig 7 in particular. This torque limiting device 50 comprises a bore 51 which is formed with a valve seat 52 at its inner end and having threads 53 at its outer end. Into the outer end of the bore 51 there is threaded a plug 54 which is formed with a threaded coaxial bore 55. A set screw 57 is received in the bore 55 and forms an adjustable support for a coil spring 58 loading a valve ball 59 against the seat 52. A passage 60 on one side of the valve 52, 59 communicates with the fluid chamber compartment 38, whereas another passage 61 interconnects the other side of the valve 52, 59 and the chamber compartment 39. The inertia drive member 10 comprises a fluid passage through which a bypass flow may be established between the two fluid chamber compartments 38, 39. This fluid passage comprises an annular valve chamber 70 axially defined by the end closure 20 and an annular disc 71. See Fig 9. The valve chamber 70 is divided by two diametrically opposed lands 72, 73 into a first section 75 and a second section 76. See Fig 8. The first valve chamber section 75 communicates with fluid chamber compartment 38 through a number of openings 77 in the end closure 20, whereas the second section 76 communicates with fluid chamber compartment 39 through openings 78. On the opposite side of the disc 71 there is a circular passage 79 which continuously communicates with both of the valve chamber sections 75, 76 via openings 80 and 81, respectively, in the disc 71. In the valve chamber 70 there is supported an annular leaf spring valve element 82. As illustrated in Fig 9, the latter has a part-cylindrical nominal, unloaded shape and is rigidly clamped between the diametrically opposite lands 72, 73 and the disc 71. Thereby, the valve element 82 forms two separately acting semi-circular valve members 82A, 82B, one of which 82A acting in the first valve cham ber section 75 to control the fluid flow through the openings 80 in the corresponding part of the disc 71 during forward rotation of the tool, and the other 82B acting in the second valve chamber section 76 to control the fluid flow through the openings 81 in that part of the disc 71 during reverse rotation of the tool. In Fig 8 a segment of the valve element 82 has been cut away to expose the openings 77 in the end closure 20. The operation order of the impulse mechanism shown in Figs 1 to 7 is described below with particular reference to Figs 2 to 5. The inertia drive member 10 receives rotational power from the motor of the tool via splined shaft 24 and socket portion 23. The inertia member 10 is rotated in a clockwise direction as illustrated by arrows in Fig 2 to 5. To begin with, let us assume that a torque resistance in the screw joint being tightened has already been built up and that the parts of the impulse mechanism occupy the very positions shown in Fig 2. In this sequence of the operation, the piston 30 is just about to complete its return stroke in a direction from the fluid chamber compartment 38 to the opposite compartment 39. This is accomplisehd by the cooperation of the cam surface 42 on the output spindle 11 and the gradually sloping cam surface 44 on the piston 30. During its return stroke, the piston 30 has changed the volumes of the two fluid chamber compartments 38, 39 such that the volume of compartment 38 is increased whereas compartment 39 has become smaller. In the very position shown in Fig 2, the two compartments 38, 39 are still sealed off relative to each other, since the seal postion 31 of the piston 30 is in contact with pin 28. During the limited portion of the piston return stroke when sealing contact between seal portion 31 and pin 28 exists, a certain pressure difference between the two compartments 38, 39 arises. Due to the fact, however, that the cam surface 44 on the piston 30 is just gradually sloping inwards and that it is located at a relatively big distance from the fulcrum 27 of the piston 30, the piston speed during the return stroke is relatively low. This means that the flow of fluid through the valve chamber 70 and the openings 77, 80 is rather slow and a small pressure drop only arises across valve member 82A. This pressure drop is too small to make the valve member 82A shift from open condition to closed condition. Accordingly, fluid is free to pass from compartment 39 to compartment 38. As a result of the valve controlled bypass there is virtually no fluid flow resistance during the piston return stroke. At continued rotation of the inertia drive member 10 and piston 30 relative to the output spindle 11, the abruptly inclined cam surface 43 on the piston 30 gets into contact with the cam surface 42 on the output spindle 11. This position, illustrated in Fig 3, means the beginning of the impulse generating work stroke of the piston 30. Since the abruptly inclined cam surface 43 of the piston 30 meets the abruptly inclined cam surface 42 on the output spindle 11 and since the contact point of the cam surfaces is relatively close to the piston fulcrum 27 and the speed of the inertia member 10 has increased further a very fast acceleration of piston 30 is accomplished. At the very start of the impulse stroke, communication is still maintained between the two fluid chamber compartments 38, 39, because the seal portion 31 has not yet reached the seal pin 28. See Fig 3. After a very short time interval, however, the seal portion 31 has established a fluid seal between the compartments 38, 39 by cooperating with seal pin 28. This position is shown in Fig 4. The fluid velocity past valve 82A increases rapidly and the pressure drop across valve 82A instantaneously reaches a level where the latter is automatically shifted from open condition to closed condition. Thereat, the valve 82A sealingly covers the openings 80 in the disc 71. Due to the abruptly shaped cam surface s 43 and 42 and their close location relative to the piston fulcrum 27, the kinetic energy of the rotating inertia drive member 10 is transformed into a pivoting movement of the piston 30 in a very efficient way. However, the back pressure in the right hand fluid chamber compartment 38 is very high and corresponds to the kinetic energy of the inertia drive member 10 which is transferred to the piston 30 via the fulcrum pin 27. The big pressure difference now obtained between the two fluid chamber compartments 38, 39 brings the piston 30 abruptly to a stand still relative to the drive member 10. The result of this heavy, suddenly arisen hydraulic pressure acting on the piston 30 is that all the kinetic energy received from the inertia drive member 10 is transferred onto the output spindle 11 via the cam surfaces 43 and 42. A torque impulse is being delivered to the output spindle 11. As the kinetic energy has been transferred to the output spindle 11 and the rotation speed of the inertia drive member 10 is brought down to stand still, the pressure difference across the piston 30 is substantially reduced. Due to the decreased pressure difference between the two fluid chamber compartment 38, 39 as well as across the leaf spring valve member 82A the latter returns immediately and automatically to its open position. This means that fluid communication is reestablished through openings 77, valve chamber section 75, openings 80 in the disc 71, passage 79, openings 81, valve chamber section 76 and openings 78. Thereby, the piston 30 does not have to overcome any fluid flow resistance during its remaining movement under sealing engagement with pin 28. Having its abruptly inclined cam surface 43 still in contact with the cam surface 42 on the output spindle 11, the piston 30 is pivoted further to the right such that the sealing contact between seal portion 31 and seal pin 28 is definitely broken. See Fig 5. At continued rotation of the inertia drive member 10 relative to the output spindle 11, the edge of the piston cam surface 43 slips past the outer corner of the output spindle cam surface 42. See Fig 5. From that on the piston 30 and the inertia drive member 10 are free to rotate for about half a revolution relative to the output spindle 11 without anything happening. When, however, such a 180 degree relative rotation is completed, the gradually sloping cam surface 44 of the piston 30 starts engaging the outer corner of the cam surface 42 on the output spindle 11. At continued relative rotation, another return stroke of the piston 30 is performed. As being described above, the return stroke is comparatively slow and does not give rise to any fluid flow that is strong enough to make the leaf spring valve 82B shift to closed condition. At a predetermined pretension level in the screw joint the pressure peaks in the fluid chamber 19 reach a magnitude at which the valve ball 59 is lifted from the seat 52 against the action of the spring 58. Hydraulic fluid is then bypassed from the high pressure chamber compartment 38 to the low pressure compartment 39. Thereby, the output torque of the tool is limited. When the tool is operated in the opposite direction, for example at untightening a joint or tightening a left-hand threaded joint, high pressure is built up in the fluid chamber compartment 39 which results in a fluid flow in the opposite direction through the valve chamber 70 and the passage 79. However, during the torque impulse generating pressure peak the valve member 82B sealingly covers the openings 81 in the disc 71 in the same way as described above in connection with the opposite direction of tool rotation.

Claims: 1. Hydraulic torque impulse tool, comprising a housing (12), an inertia drive member (10) coupled to a rotation motor in said housing and including a fluid chamber (19), an output spindle (11) having an impulse receiving rear portion extending into said fluid chamber (19), an impulse generating seal means (30) movably arranged in said fluid chamber (19) and dividing the latter into a high pressure compartment (38) and a low pressure compartment (39) during a limited portion of its movement relative to said fluid chamber (19), a fluid passage means (70; 79) extending past said seal means (30), and a pressure responsive valve means (82) arranged to control the flow through said passage means (70;79) by shifting automatically from an open condition to a closed condition as the difference in pressure between said high pressure compartment (38) and said low pressure compartment (39) exceeds a certain level, characterized in that said fluid passage means comprises a valve chamber (70) located in one of the end walls (20) of said inertia drive member (10) and having one or more fluid communication openings (80, 81), and said valve means (82) comprises an annular leaf spring washer mounted in said valve chamber (70) in a plane substantially transverse to the rotation axis of said drive member (10) and being arranged to be elastically deformed by the fluid pressure to thereby control the fluid flow through said communication openings (80,81). 2. Torque impulse tool according to claim 1, wherein said annular leaf spring washer (82) has a non-flat nominal shape in its unloaded condition. 3. Torque impulse tool according to claim 2, wherein said leaf spring washer (82) has a part-cylindrical shape in its unloaded condition. 4. Torque impulse tool according to anyone of claims 1-3, wherein said valve chamber (70) is annular in shape and divided substantially along a diameter line into a first section (75) which is connected to said high pressure compartment (38) and which comprises one or more of said fluid communication openings (80), and a second section (76) which is connected to said low pressure compartment (39) and which comprises one or more of said fluid communication openings (81), said leaf spring washer (82) extending through both of said first and second sections (75, 76) and being arranged to control said fluid communication openings (80) of said first section (75) at tool rotation in the normal "forward" direction and to control said fluid communication openings (81) of said second section (76) at tool rotation in the "reverse" direction.

Inventors: SCHOEPS, KNUT CHRISTIAN
Applicants: ATLAS COPCO AKTIEBOLAG
Application year: 1985
Main classification: B25B21
IPC codes: B25B21, B25B23, B25D15