HYDRAULIC PULSE WRENCH

Abstract: An improved hydraulic pulse wrench provided with a hydraulic pulse generator which comprises a liner, an anvil rotatably mounted in the liner and formed with a longitudinal slit, two blades loosely mounted in the longitudinal slit. The liner has an elliptic hole. The two blades have their outer edges beveled in different directions. The anvil is formed with a pair of axial ridges and the liner is formed on its inner periphery with a total of five axial ridges. The blades, anvil and liner cooperate with one another to form pressure chambers while the liner is rotated.

Description: The present invention relates to a hydraulic pulse wrench provided with a hydraulic pulse generator which works as a substitute for a conventional striking tool such as a mechanical impact mechanism. A hydraulic pulse wrench is known which has a hydraulic pulse generator rotatably mounted in a casing and including a liner and an anvil provided with blades, an output shaft integral with the anvil and protruding from the front end of the casing, and an air motor provided at rear of the liner for driving the liner. A turning tool secured to the end of the output shaft is mounted on a nut or the like to tighten or loosen it. When the resistance to the anvil increases to prevent it from rotating with the output shaft in tightening a nut or the like, the oil confined between the liner and the anvil produces an impact turning torque. Such an impact torque is generated owing to a high pressure created in one of a pair of oil chambers formed between the anvil and the liner and partitioned by a blade. Since it is a common practice with the prior art torque wrench to use a single blade and thus to shape the anvil and the liner asymmetrically in cross-section, vibrations are inevitably generated. In order to provide a large impact force, it is required to provide a large-sized blade. To accommodate such a blade, the wrench itself also has to be large in size. Some of the prior art wrench employ a two- or four-blade construction. But they are rather complicated in mechanism and thus troublesome to assemble. UK Patent Application GB-2136719A discloses a power driven wrench comprising a hydraulic impulse torque generator which in turn comprises an oil filled liner having a general oval internal profile and an output shaft mounted coaxially within the liner. The shaft carries two blades slidably mounted in slots and has ceiling ribs generally at right angles to the slots. The liner has at least four seal points formed at circumferentially spaced locations on the inner circumferential surface of the liner, the centre of two opposing seal points being made eccentric by several degrees relative to a straight line extending through the centre of the liner chamber. The blades form seals with the sealing points so that one impulse is produced on the output shaft in each revolution of the liner relative to the shaft and is applied to both of the blades so that improved balance of output torque is achieved. US Patent No 3196636 discloses a sealing device for an impulse tool having a fluid type spindle means with sealing device increases the impulse power of the impulse tool and provides only one impulse per revolution of the rotating elements of the impulse tool. The sealing device furthermore substantially eliminates leakage of the fluid from the high pressure portion of the cavity in the inner housing of the tool to the lower pressure portion during impulse action and eliminates the conventional gating slot in the spindle blade. This is achieved by providing an improved sealing device having a housing means adapted to contain a fluid, drive means operatively associated with one the housing means and the spindle means for causing relative rotary movement between the housing means and the spindle means, the other of the housing means and the spindle means being adapted to engage the object. The through type spindle blade in the spindle means is engageable with a land means in the housing once during each revolution of the relative rotary movement to dynamically seal off a portion of the fluid so that the pressure in the portion increases thereby causing the other of the housing means and spindle means to rotate with respect to the one and to apply a torque to the object. One of the land means and the spindle blade being offset from a centre line of the one. With the pulse wrench according to the present invention, as with the prior art, while the resistance to rotation of the output shaft is relatively small, the anvil rotates, keeping pace with the liner with the oil interposed therebetween. But, as the nut is tightened harder and offers more resistance, the anvil begins to fall behind the line in the speed of rotation, until the sealing ridges on the anvil get into sealing contact with the corresponding sealing ridges on the liner and simultaneously the top ends of the blades sealingly contact the respective sealing ridges on the liner to increase the oil pressure in the high-pressure chambers and produce an impact. Another half turn of the liner from this postion will bring the sealing ridges on the anvil again into sealing contact with the corresponding sealing ridges on the liner, but keep the outer ends of the blades space apart from the corresponding sealing ridges on the liner. Thus no increase in the oil pressure occurs in this position. It will be appreciated from the foregoing that one impact is produced for every rotation of the liner. Since the anvil of the present invention, which is defined in claim 1, is provided with two blades to give one impact for each rotation, the anvil and liner do not have to be formed asymmetrically. This minimizes the generation of vibrations. The blades mounted in the anvil have their outer ends tapered or beveled in different directions so that the line connecting the tips of the blades will be in an offset position with respect to the center of rotation of the anvil. Thus the anvil can take a perfect laterally symmetrical shape. Also since the two blades have the same shape in common and have only to be mounted oppositely to each other when assembling, they are easy to manufacture as well as to assemble. The anvil is formed on its outer periphery with an opposed pair of axial sealing ridges in a direction perpendicular to the blade mounting portions. The liner is formed on its inner periphery with the axial sealing ridges in the direction of breadth of the inner periphery adapted to sealingly contact the sealing ridges on the anvil and with the axial sealing ridge in the direction of its length at one side adapted to sealingly contact the tip of the blade whether in the normal or reverse turn position and at the other side with the two axial sealing ridges each adapted to sealingly contact the tip of the blade when in the normal turn position and in the reverse turn position, respectively. Thus a sufficient impact will be created both in the normal and reverse turn positions. Other objects of the present invention will become apparent from the following description taken with reference to the accompanying drawings, in which: Fig. 1 is a vertical sectional side view of a portion of the pulse wrench according to the present invention; and Figs. 2 - 4 are enlarged cross-sectional views showing how the pulse wrench operates. Referring to the drawings, numeral 1 in Fig. 1 designates a body of the pulse wrench embodying the present invention. A conventional air motor is mounted in the body. At the bottom of the body 1 is formed a handle 2 in which are mounted a valve for switching on and off the air motor and a valve for reversing the direction of rotation of the air motor. These valves are actuated by an ON/OFF lever 3 and a lever 4 for reversing the direction of rotation which are provided in front of the handle 2. To the front end of the body 1 is fixedly mounted a casing 5 which houses a hydraulic pulse generator A according to the present invention. This power transmission device comprises an anvil 6, a liner 7 mounted on the anvil 6 and two blades 8 and 9 loosely mounted in a longitudinal slit cut through the anvil 6. The liner 7 has an elliptic inner periphery arranged eccentrically with respect to the center of rotation of the anvil 6. The blades 8 and 9 are biased by springs 14 away from each other so as to be pressed against the inner surface of the liner 7. The liner 7 is provided at its front end with a front wall 10 and at its rear end with a rear wall 11. On the front end of the anvil 6 is provided an output shaft 12 protruding through the front wall 10. On the back of the rear wall 11 is integrally provided a shaft 13 which is connected to the output shaft of the air motor. The liner 7 is rotatable with respect to the anvil 6 and is formed on its inner periphery with an opposed pair of axial sealing ridges 15 and 16 in the direction of minor axis of the ellipse and with an axial sealing ridge 17 at one side in the direction of its major axis and two axial sealing ridges 18 and 19 at the other side. The anvil 6 has in turn an opposed pair of axial sealing ridges 21 and 22 on its outer periphery adapted to sealingly contact the sealing ridges 15 and 16 on the liner, respectively. The blades 8 and 9 have their outer ends 23, 24 tapered or beveled. Since they are beveled in different or asymmetrical directions, the line connecting the ends 23 and 24 is offset with respect to the center of rotation of the anvil 6. A relief valve 25 provided in a relief duct serves to adjust the flow rate through the duct and thus to adjust the impact strength. An automatic oil supply unit B comprises an axial oil storage chamber 30, a pressure valve 31 slidably mounted in the chamber and a spring 32 for biasing the valve 31 to pressurize the chamber. The oil storage chamber 30 is formed with a female thread in its rear periphery into which is inserted a screw plug 33. The oil storage chamber 30 has its front portion in communication with the low pressure chamber b through a narrow hole 34. In assembling, after the front portion of the chamber 30 has been filled with oil, the valve 31, the spring 32 and a collar 35 are inserted one after the other into the chamber 30, leaving enough space between the valve 31 and the collar 35 to allow the valve 31 to move back. Finally the screw plug 33 is put into threaded engagement with the female thread to seal up the rear end of the chamber 30. "O" rings are fitted in annular grooves formed in the outer periphery of the valve 31 and in the front outer periphery of the screw plug 33 to maintain the airtightness and liquid-tightness in the chamber 30. In operation, a turning tool fixed to the end of the output shaft 12 is mounted on a nut to be tightened and the lever 3 is pressed with the lever 4 set in a normal turn position. The air motor will start to turn the liner 7 of the hydraulic pulse generator A clockwise in the direction of arrows in Figs. 2, 3 and 4. At the beginning, since the nut scarecely meets resistance, the rotataion of the liner 7 is smoothly transmitted through oil in high-pressure chambers a to the blades 8 and the anvil 6 to rotate the output shaft 12 and thus the nut at a high speed. As the nut is turned to tighten the object harder, the load on the nut grows gradually, so that the nut will become difficult to turn, thus increasing the resistance to the anvil 6. Since the liner 7 keeps rotating at a constant speed all the while, the anvil 6 and the blades 8 and 9 begin to fall behind the liner 7 in the speed of rotation, which results in the contraction of the volume of the high-pressure chambers a and the expansion of the volume of low-pressure chambers b . In the state shown in Fig. 2, the sealing ridges 21 and 22 on the anvil 6 get into sealing contact with the sealing ridges 15 and 16 on the liner and at the same time the sealing ridges 17 and 18 on the liner 7 get into sealing contact with the end faces 23 and 24 of the blades 8 and 9, respectively, where a high pressure is created in each high-pressure chamber a . The high-pressure oil in the chambers acts on the blades 8 and 9, giving an impact on the anvil 6 to produce a desired impact torque. When the liner 7 further turns by 90 degrees to the position shown in Fig. 3, the sealing ridges 21 and 22 on the anvil 6 are kept clear of any of the sealing ridges 15, 16, 17, 18 and 19 on the liner 7, keeping the chamber formed between the anvil 6 and the liner 7 at the same pressure level. Thus in this state no impact is produced. When the liner 7 turns further by 90 degrees to the position as shown in Fig. 4, the sealing ridges 21 and 22 on the anvil 6 are brought into sealing contact with the sealing ridges 16 and 15 on the liner 7, respectively, whereas the blades 8 and 9 are clear of any of the sealing projections 17, 18 and 19 on the liner 7, putting the high-pressure chambers a in communication with the low-pressure chambers b . Thus in this state, no impact is produced either. When the liner 7 further turns from the position of Fig. 4 by 180 degrees in the same direction to return to the position of Fig. 2, another impact is produced. When the liner 7 is turned in the reverse direction, the blades 8 and 9 will be inclined opposite to the way as shown in the drawings. Thus an impact force is produced at the position of Fig. 4. Part of the oil in the high-pressure chamber a flows to the low-pressure chamber b through a passageway 26 with its flow rate throttled on its way by the relief valve 25 so as to control the increase in the pressure difference between the chambers a and b below a predetermined value, thus keeping the impact torque which acts on the blades 8 within a uniform level. This action takes place in every rotation of the liner 7 to impart an impact torque to the output shaft 12 and tighten the nut. In order to loosen the nut, the lever 4 is shifted to the reverse position to reverse the air motor, thus reversing the hydraulic pulse generator. As the wrench is operated, the oil in the chambers a and b partially leaks to reduce its volume in the chambers. In this embodiment, however, since the oil in the storage chamber 30 is normally pressurized by the pressure valve 31 biased by the spring 32, part of the oil in the chamber 30 will flow into the chambers a and b through the narrow hole 34 whenever there is a reduction in the volume of oil in the chambers a and b to make up for such a reduction. In another embodiment shown in Fig. 6, a high pressure gas is sealed in between the valve 31 and the screw plug 33 to pressurize the valve 31. This arrangement performs substantially the same function as that shown in Fig. 5. It is usually difficult for the torque wrench of this type to keep on operating for a long time without causing the oil temperature in the liner 7 to rise and thus causing its volume to expand. Since such an expansion of volume of the oil makes it difficult a normal operation of the relief valve 25 and thus hampers a smooth rotation to produce an impact torque. It is necessary to provide an accummulator in the liner to suck up any excess oil. According to the present invention, the valve 31 of the automatic oil feeding assembly B can move backwardly to increase the volume of the storage chamber 30 to act as an accumulator. However, since the storage chamber 30 is small in volume for an accumulator, it is preferable to provide an accumulator besides the storage chamber 30.

Claims: A hydraulic pulse wrench having a casing (5), an output shaft (12), a drive means, and a hydraulic pulse generator comprising a liner (7) adapted to be driven by said drive means, an anvil (6) rotatably mounted in said liner and formed with a longitudinal slit, and two blades (8, 9) loosely mounted in said longitudinal slit in opposite directions and coacting with said liner and said anvil to form oil chambers when said anvil is in predetermined angular positions with respect to said liner so that the oil pressure sealed in said oil chambers will product impact torques, said liner having an elliptic inner peripher, characterised in that said two blades have their outer edges beveled in different directions so that a line connecting the tips of said two blades will be in an offset position with respect to the centre of rotation of said anvil, that said anvil is formed with an opposed pair of axial sealing ridges (21, 22) on its outer periphery in a direction perpendicular to said longitudinal slit, and that said liner is formed on its inner periphery with an opposed pair of axial sealing ridges (15, 16) in the direction of minor axis of the ellipse and an axial sealing ridge (17) at one side in the direction of major axis of the ellipse and two axial sealing ridges (18, 19) at the other side. A hydraulic pulse wrench as claimed in claim 1, further comprising an oil supply unit for replenishing oil to said oil chambers.

Inventors: DAININ, TAKASHI
Applicants: NIPPON PNEUMATIC MANUFACTURING CO. LTD.
Application year: 1987
Main classification: B25B21
IPC codes: B25B23, B25B21