Reversible power wrench

Abstract: A reversible power wrench comprises a housing (10), a rotation motor, and a power transmission coupling the motor to an output shaft (21), including a reduction gearing (20) with first planetary gearing (28) for transferring torque in the "forward" direction of rotation and a second planetary gearing (29) for transferring torque in the "reverse" direction of rotation. The first and second planetary gearings (28, 29) have rotationally interconnected sun gears (31, 39) and a common planet wheel carrier (34). The second planetary gearing (29) comprises an inner set of planet wheels (37) intermeshing with the sun gear (39) and an outer set of planet wheels (38) intermeshing with the inner set of planet wheels (37) and engageable with a ring gear (40) which is axially shiftable between an "forward" position in which it engages the planet wheels (33) of the first planetary gearing (28) only and a "reverse" position in which it engages the outer sets of planet wheels (38) of the second planetary gearing (29) only. Speed responsive centrifugal weights (46) prevent by positive locking the ring gear (40) from being shifted during operation of the power wrench.

Description: This invention relates to a reversible power wrench of the type having the features of the preamble of claim 1 known from US-A-4364286. The most common way of obtaining reversability of a pneumatic power wrench is simply to reverse the drive motor. A problem concerned with pneumatic vane-type motors, which is the most suitable type of motor for power wrenches, is that such motors usually have a considerably less power output in the reverse direction of rotation than in the normal forward direction. This is due to nonsymmetric locations of the air communication ports in the motor, the purpose of which is to obtain a high as possible power output of the motor in the forward direction of rotation. In order to get a higher power output in the reverse direction, some previously known pneumatic power wrenches have been provided with symmetrically designed vane type motors. That is a compromise which results in a lower power output in the forward direction of rotation. Owing to the lower power output, a bigger motor has to be used to get the same power output in the forward direction as for an optimized non-symmetric motor. This results in a bulkier and heavier tool and a higher pressure air consumption. A particular problem to accomplish alternative directions of rotation exists at twin motor powered wrenches, like the one described in US Patent No. 4,484,871. Due to the fact that the power transmission comprises a one-way clutch the motors in this type of tool are not reversible. One way to accomplish a reversible pneumatic power wrench is to use a reversing gearing by which the direction of rotation is shiftable without changing the direction of rotation of the motor. This means that an optimized nonsymmetric vane type motor can be used for obtaining a high power output in both directions of rotation. The employment of a reversing gearing also solves the problem of how to accomplish a change of rotation direction at twin motor wrenches of the type described in the above mentioned US Patent No. 4,484,871. A reversing gearing for a power wrench in the form of an attachment unit is previously described in US Patent No. 2,780,944. The primary object of the invention is to provide a pneumatic power wrench having a power transmission with a combined reduction and a reversing gearing which is shiftable between a "forward" condition and a "reverse" condition, and which is compact and simple in structure and easy to operate. Another object of the invention is to provide a reversible power wrench having a reversing gearing with a speed responsive safety lock which permits shifting of the gearing between its "forward" condition and its "reverse" condition at rotation speeds below a certain level only. Further characteristics and advantages of the invention will appear from the following description in which a preferred embodiment of the invention is described in detail with reference to the accompanying drawings. On the drawings: Fig 1 shows a partly broken side view of a power wrench according to the invention. Fig 2 shows a longitudinal section through the reversing gearing, illustrating the "forward" condition. Fig 3 is a view similar to Fig 2, but illustrates the "reverse" condition of the gearing. Fig 4 shows a cross section along line IV-IV in Fig 3. Fig 5 shows a cross section along line V-V in Fig 3. Fig 6 shows a cross section along line IV-IV in Fig3, illustrating the safety lock means in an inactive condition. Fig 7 shows the same cross section as in Fig 6, but illustrates the safety lock means in an active condition. The power wrench shown on the drawings comprises a housing 10 including a main section 11 formed with a pistol grip handle 12. The main section 11 of the housing 10 encloses a pneumatic drive unit in the form of two vane motors (not shown). The motors are supplied with pressure air via an inlet passage extending through the handle 12, and a throttle valve 13. The housing 10 also comprises a forward casing 14 which encloses a power transmission and which is swivelled relative to the main section 11. A reaction support bar 15 is firmly secured to the casing 14 by a nut 16. The casing 14 is arrestable in anyone of a number of angular positions defined by indentations 17 located around the rear periphery of the casing 14. These indentations 17 are arranged to be engaged by a latch mechanism (not shown) operably coupled to the throttle valve 13. This type of swivel and latch arrangement is previously known and described in detail in the above mentioned US 4,484,871. In the transmission casing 14, there is located a reduction gearing 20 which is shiftable for obtaining alternative directions of rotation of an output shaft 21. The output shaft 21 is square ended for receiving a standard type nut socket. In Fig 1, there is illustrated a manoeuver means in the form of a tubular grip element 23 which is axially displaceable on a tubular sleeve 22 which is mounted on the casing 14 and axially locked by a lock ring 19. The grip element 23 is connected to the reduction gearing 20 inside the casing 14. For the purpose of illustration, the grip element 23 is shown in Fig 1 with a broken-away portion 24 through which is visible one of three identical Z-shaped apertures 25 in the casing 14. These apertures 25, which infact are covered by the grip element 23, form a guiding means for three radial pins 27 connecting the grip element 23 to the reduction gearing 20 inside the casing 14. The apertures 25 and the radial pins 27 are equally distributed along the circumference of the casing 14 and ring gear 40, respectively. The functional features of the pins 27 and apertures 25 will be described in further detail below. As shown in Figs 2-5, the reduction gearing 20 comprises a first planetary gearing 28 and a second planetary gearing 29, whereof the first planetary gearing 28 is intended to accomplish a speed reduction in the "forward" direction and the second planetary gearing 29 in the "reverse" direction. By the expression "forward" is meant the main or predominant direction of rotation in which the wrench is intended to rotate for performing its main task, namely to tighten screw joints. In almost all cases this means a clockwise rotation. By "reverse" rotation, it is accordingly meant the direction of rotation opposite the "forward" direction, usually the anticlockwise direction. The first planetary gearing 28 comprises a sun gear 31 cut directly in a drive spindle 32. The latter is connected to the drive unit and supplies high speed rotational power to the reduction gearing 20. The first planetary gearing 28 further comprises three planet wheels 33 which are rotatively journalled on stub axles 30 mounted on a planet wheel carrier 34. The planet wheels 33 intermesh with the sun gear 31. The planet wheel carrier 34 is rigidly interconnected with a transmission shaft 35 by which the rotational power is transferred to the output shaft 21, directly or via a further speed reducing gearing. (Not shown). Moreover, the planet wheel carrier 34 is common for both of the two planetary gearings 28, 29 and, accordingly, forms a support means for the planet wheels of the second planetary gearing 29. These planet wheels comprise an inner set of planet wheels 37 and an outer set planet wheels 38. The inner sets of wheels 37 are journalled on stub axles 36a and intermesh both with a sun gear 39 and the outer set of wheels 38, whereas the outer set of wheels 38 are journalled on stub axles 36b and intermesh with the inner set of wheels 37 as well as with an axially shiftable ring gear 40. The sun gear 39 is not only rotatively interconnected with the sun gear 31 of the first planetary gearing 28, it is in fact out in the same shaft, namely the drive spindle 32. However, the sun gear 39 has fewer teeth than the sun gear 31. The ring gear 40 is shiftably guided in the casing 14 between a "forward" position and a "reverse" position, and a spring 41 exerts a biassing force on the ring gear 40 towards the "forward" position. The spring 41 is disposed on the outside of the casing 14 and is covered by the sleeve 22 which forms an axial support for the spring 41. When occupying its "forward" postion, the ring gear 40 engages the planet wheels 33 of the first planetary gearing 28. This position is illustrated in Fig 2. The ring gear 40 is locked against rotation relative to the casing 14 by means of the three radial pins 27 extending through the apertures 25 in the casing 14, which means that the reaction torque from the planet wheels 33 is transferred to the casing 14. This means in turn that a driving torque is transferred to the planet wheel carrier 34 and to the transmission shaft 35. A clockwise rotation of the drive spindle 32 results in a clockwise rotation of the transmission shaft 35. In its "reverse" position, illustrated in Fig 3, the ring gear 40 engages the outer planet wheels 38 of the second planetary gearing 29, and because the outer planet wheels 38 engage the inner planet wheels 37 instead of the sun gear 39, the reaction torque transferred to the ring gear 40 as well as the direction of rotation of the planet wheel carrier 34 is directed oppositely compared to the "forward" condition. In other words, the transmision shaft 35 now rotates in the "reverse" direction. As illustrated in Fig 1 and 2, the grip element 23 occupies its rearmost position on the casing 14 as the ring gear 40 is in its "forward" position, and to indicate the actual direction of rotation a row of arrows 42 depicted on the sleeve 22 is uncovered by the grip element 23. See Fig 1. Through the broken-away portion 24 of the grip element 23 in Fig 1, it is to be seen that the radial pins 27 occupies its rearmost positions relative to the Z-shaped apertures 25. In order to shift the gearing from "forward" to "reverse" condition, the grip element 23 is displaced forwardly on the casing 14, against the bias force of spring 41. Depending on the particular shape of the apertures 25, the grip element 23 has to be rotated a certain angle to make the pins 27 enter the forwardmost parts of the apertures 25 and, thereby, allow the ring gear 40 to be displaced fully into its "reverse" position. Due to the continuous action of the bias spring 41 the grip element 23 and the ring gear 40 has to be manually maintained in the "reverse" position. As the manual shifting force applied on the grip element 23 is discontinued, the spring 41 returns automatically the ring gear 40 to its central free running position in which the pins 27 rest against the transverse portions of the Z-shaped apertures 25. As the ring gear 40 is shifted forwardly relative to the casing 14 to occupy its "reverse" position, the grip element 23 covers the arrows 42 but uncovers on its other side another row of arrows (not illustrated) pointing in the opposite direction to indicate the actual direction of rotation. Since the transmission casing 14 is swivelled to the main section 11 of the housing 10 to enable any suitable support position of the reaction support bar 15, the direction indicating arrows 42 as well as the nonillustrated oppositely directed arrows are disposed around the entire circumference of the sleeve 22 to be visible at all times. An important feature of the reduction gearing 20 as described above is that the axial distance between the planet wheels 33 of the first planetary gearing 28 and the outer planet wheels 38 of the second planetary gearing 29 is equal to or larger than the axial extent of the ring gear 40. This means that when occupying a central position, defined by the transverse portions of the Z-shaped apertures 25, the ring gear 40 is out of engagement with both the first planetary gearing 28 and the second planetary gearing 29. This central position of the ring gear 40 provides a free running condition which ensures that no dead lock condition of the reduction gearing 20 may occur. In Figs 6 and 7, there is illustrated a safety lock means 45 by which unintentional gear shifting during tool operation is prevented. A shifting of the direction of rotation during operation of the wrench would be hazardous to the operator, because the reaction support bar 15, which originally has been located so as to take support against a fixed structure adjacent the screw joint being tightened, would in case of a sudden change in direction of rotation swing freely until it hits another fixed structure. Such a swinging movement of the reaction support bar 15 may cause damage to the equipment and workpiece and injure the operator. In order to eliminate this safety risk, there is provided a speed responsive lock means 45 by which shifting of the ring gear 40 is prevented during operation of the wrench. This lock means 45 comprises three arc-shaped centrifugal weights 46 each of which is pivotally supported on one of the stub axles 30 and located in a pocket 47 in the planet wheel carrier 34. The centrifugal weights 46 are pivotable between inner inactive positions, as illustrated in Fig 6, and outer active lock positions. See Fig 7. Springs 48 bias the centrifugal weights 46 toward their inactive positions. In their active lock positions, which are attained a certain rotation speed of the reduction gearing 20, the centrifugal weights 46 form a lock means for positively blocking the ring gear 40 against displacement from either of its "forward" or "reverse" positions. It is to be understood that the above described device is just a preferrable example and the embodiments of the invention are limited to the scope of the claims only.

Claims: Power wrench, comprising a housing (10,14), a rotation motor and a power transmission coupling said motor to an output shaft (21,35), said power transmission including a reduction gearing (20) shiftable so that said output shaft rotates in a forward drive direction or a reverse drive direction, said reduction gearing comprising -- a first planetary gearing (28) which has a sun gear (31) and planet wheels (33) and which is engagable with a ring gear means to transmit power in the forward drive direction and -- a second planetary gearing (29) which comprises a set of inner planet wheels (37) and a set of outer planet wheels (38) arranged to mesh with said inner planet wheels and which is engagable with said ring gear means to transmit power in the reverse drive direction, -- said planet wheels (33) of said first planetary gearing, said inner and outer planet wheels (37, 38) of said second planetary gearing being journalled on a common planet wheel carrier (34), characterized in that said sun gear (31) of said first planetary gearing (28) is rotationally interconnected with a sun gear (39) of said second planetary gearing (29), which sun gear (39) meshes with said inner planet wheels (37) of said second planetary gearing (29), said ring gear means is a ring gear (40) which is axially shiftable in said housing (10, 14) between -- said forward drive position in which said ring gear engages said planet wheels (33) of said first planetary gearing (28) only, and -- said reverse drive position in which said ring gear engages said outer planet wheels (38) of said second planetary gearing (29) only. Power wrench according to claim 1, wherein said sun gear (31) of said first planetary gearing (28) and said sun gear (39) of said second planetary gearing (29) are formed in one piece. Power wrench according to claim 1, wherein said planet wheels (33) of said first planetary gearing (28) are axially spaced from said outer set of planet wheels (38) of said second planetary gearing (29) by a certain distance, and said ring gear (40) has an axial extent that is equal to or smaller than said certain distance to avoid double engagement and dead locking of the reduction gearing (20). Power wrench according to anyone of claims 1-3, wherein said ring gear (40) is coupled to a maneuver means (23) which is movably guided on said housing (10, 14), and that a spring means (41) is arranged to exert a bias force on said ring gear (40) toward said "forward" position. Power wrench according to claim 4, wherein said maneuver means (23) comprises a grip element which is axially shiftable as well as rotatable relative to said housing (10, 14), and interacting stop means (25, 27) on said housing (10, 14) and said grip element (23), which require a certain angular displacement of said grip element (23) for enabling axial shifting of said ring gear (40) from said "forward" position to said "reverse" position and vice verse. Power wrench according to claim 5, wherein said stop means (25, 27) defines an axial position of said ring gear (40) in which the latter occupies a neutral unengaged position between said planet wheels (33) of said first planetary gearing (28) and said outer set of planet wheels (38) of said second planetary gearing (29). Power wrench according to anyone of claims 1-3, wherein a speed responsive lock means (45) is provided to prevent axial displacement of said ring gear (40) at rotation speeds of said reduction gearing (20) above a certain predetermined level. Power wrench according to claim 7, wherein said lock means (45) comprises at least one centrifugal weight (46) pivotally mounted on said planet wheel carrier (34) for movement between an inner inactive position and an outer lock position, and a spring means (48) connected to said at least one centrifugal weight (46) for biassing the same toward said inactive position.

Inventors: HELLSTROEM TORE GUNNAR, HELLSTROEM, TORE GUNNAR, Hellström, Tore Gunnar
Applicants: ATLAS COPCO TOOLS AB
Application year: 1995
Main classification: B25F5
IPC codes: B25F5, F16H3, B25B21