Disc brake piston retraction tool

A piston retraction tool is provided. The tool can be operated with one hand. When an operating handle is operated, the helical movements of a first external thread and a second external thread drive a first pressure plate and a second pressure plate to extend and move away from each other. First engaging pieces of first L-shaped elastic plates and second engaging pieces of second L-shaped elastic plates are distributed in the roots and on the crests of the first and second external threads. The helical movements of the first and second external threads don't interfere with each other because the first and second engaging pieces of the first and second L-shaped elastic plates are configured to jump along the first and second external threads independently. The helical movements of the first and second external threads will not be locked.

FIELD OF THE INVENTION

The invention relates to a disc brake piston retraction tool. The tool can be operated with one hand. When an operating handle is operated, the helical movements of a first external thread and a second external thread drive a first pressure plate and a second pressure plate to extend and move away from each other. The helical movements of the first external thread and the second external thread won't be locked, which improves the drive reliability.

BACKGROUND OF THE INVENTION

In general, auto mechanics responsible for repairing disc brakes and replacing brake pads may use various press machine tools. For these press machine tools, one difficulty is the need for professional mechanical use capabilities to achieve the retraction of one or more pistons associated with the caliper housing. Therefore, for brake repair and brake pad replacement, there is a need to operate an easy-to-use tool for retraction of one or more pistons.

There is a conventional art about a disc brake piston retractor tool. In the conventional art, the spacer bar of the reversible ratchet wrench assembly is simply pulled back and forth to push the piston back into the cylinder. However, when the spacer bar is pulled back, the coupler is not restricted from rotating reversely. When the second pressure plate is not tightly pressed against the piston, there will be a problem that the ratchet wheel is rotated reversely when the spacer bar is pulled back. Referring toFIG.1andFIG.2, when the handle1(equivalent to the spacer bar) is pulled back, the spring11pushes the plunger pin12against the surface of the nose130of the pawl13. Because the claw131is maintained at the position of the notch140of the ratchet wheel14, it still has a certain engaging force. Since the coupler15that is coaxially connected with the ratchet wheel14is not restricted from rotating reversely, the coupler15is easy to rotate reversely when the handle1is pulled back. In the case that the coupler15is rotated reversely, the pressure plate17screwed to the coupler15through the stud16may be retracted or tilted when the handle1is pulled back. In practice, the operator needs to hold the pressure plate17with the other hand to avoid this situation, but this affects the operational convenience and use of the tool.

Another conventional art is about a disc brake piston retraction tool, which can overcome the deficiency of the above-mentioned conventional tool. However, the engaging notches of the first L-shaped elastic plate of the first buckle member and the second L-shaped elastic plate of the second buckle member are pressed against the external threads. Because the engaging notches cover a plurality of roots and crests of the external threads, the first L-shaped elastic plate and/or the second L-shaped elastic plate may jump on the external threads too slowly, and the helical motion may be locked. Accordingly, the present inventor has devoted himself based on his many years of practical experiences to solve these problems.

SUMMARY OF THE INVENTION

The primary object of the invention is to provide a disc brake piston retraction tool, comprising a reversible ratchet wrench, a first pressure plate assembly, and a second pressure assembly.

The reversible ratchet wrench includes an operating handle and a ratchet wheel located at a force output end of the operating handle. A first force output shaft and a second force output shaft are disposed on two sides of a center of the ratchet wheel and extend out of two sides of the force output end of the operating handle. A surface of the first force output shaft is formed with a first external thread. A surface of the second force output shaft is formed with a second external thread. The first external thread and the second external thread are in different helical directions.

The first pressure plate assembly includes a first pressure plate, a first nut, a first sleeve unit, and a first restraining member. The first pressure plate has an outer surface and an inner surface. The first nut is fixed to the inner surface of the first pressure plate relative to the first force output shaft. The first nut has a first internal screw hole screwed with the first external thread. The first sleeve unit is made of an elastic material and sleeved on an outer surface of the first nut. A front edge of one end of the first sleeve unit has a plurality of first L-shaped elastic plates that are arranged around the first internal screw hole and extend toward the surface of the first force output shaft. The first L-shaped elastic plates each have a first engaging piece corresponding to the first external thread. The first engaging piece is engagable in a root of the first external thread. The first engaging piece has a width not more than 4 times a pitch of the first external thread. The first engaging piece has a thickness less than half of the pitch of the first external thread. The first engaging piece is configured to jump along the first external thread to generate a pressing force. The first restraining member is sleeved on a surface of the first sleeve unit for restraining the first sleeve unit on the first nut.

The second pressure plate assembly includes a second pressure plate, a second nut, a second sleeve unit, and a second restraining member. The second pressure plate has an outer surface and an inner surface. The second nut being fixed to the inner surface of the second pressure plate relative to the second force output shaft. The second nut has a second internal screw hole screwed with the second external thread. The second sleeve unit is made of an elastic material and sleeved on an outer surface of the second nut. A front edge of one end of the second sleeve unit has a plurality of second L-shaped elastic plates that are arranged around the second internal screw hole and extend toward the surface of the second force output shaft. The second L-shaped elastic plates each have a second engaging piece corresponding to the second external thread. The second engaging piece is engagable in a root of the second external thread. The second engaging piece has a width not more than 4 times a pitch of the second external thread. The second engaging piece has a thickness less than half of the pitch of the second external thread. The second engaging piece is configured to jump along the second external thread to generate a pressing force. The second restraining member is sleeved on a surface of the second sleeve unit for restraining the second sleeve unit on the second nut.

When in use, the first pressure plate and the second pressure plate of the tool are placed in an internal space of a caliper housing and located between at least one piston that is not retracted and a fixed wall. The force output direction of the reversible ratchet wrench is selective. The operating handle of the reversible ratchet wrench is pulled back and forth, and then the ratchet wheel drives the first force output shaft and the second force output shaft to rotate in one direction. The helical movements of the first external thread and the second external thread act on the first internal screw hole of the non-rotating first nut and the second inner screw hole of the non-rotating second nut, such that the first pressure plate and the second pressure plate are driven to extend and move away from each other. The fixed wall is configured to confine the movement of the first pressure plate and the second pressure plate and serves as a force support, so that the piston is retracted to the starting position in the cylinder. In the process of retracting the piston, at least one of the first engaging pieces of the first L-shaped elastic plates of the first sleeve unit and at least one of the second engaging pieces of the second L-shaped elastic plates of the second sleeve unit are pressed against the first external thread and the second external thread to provide a damping force to limit rotation of the first force output shaft and the second force output shaft. Thus, when the operating handle of the reversible ratchet wrench is pulled back, it will not drive the ratchet wheel, so that the tool can be operated with one hand. When the operating handle is operated, the helical movements of the first external thread and the second external thread drive the first pressure plate and the second pressure plate to extend and move away from each other. The first engaging pieces of the first L-shaped elastic plates and the second engaging pieces of the second L-shaped elastic plates are distributed in the roots and on the crests of the first external thread and the second external thread. The helical movements of the first external thread and the second external thread don't interfere with each other because the first engaging pieces of the first L-shaped elastic plates and the second engaging pieces of the second L-shaped elastic plates are configured to jump along the first external thread and the second external thread independently. The helical movements of the first external thread and the second external thread won't be locked, which improves the drive reliability.

Preferably, the force output end of the operating handle has an accommodating hole therein. The ratchet wheel and a pawl are pivotally connected in the accommodating hole. The pawl in the accommodating hole is pivotally connected to a side edge of the ratchet wheel via a pivot hole. The pawl has a pair of switching portions that are disposed at two ends of the pivot hole and extend out of the accommodating hole. A nose-shaped protrusion is formed on one side between the pair of switching portions. Two spaced claws each corresponding in shape to a tooth space of the ratchet wheel are formed on another side between the pair of switching portions. One side of the pawl is provided with a spring installed in a long groove to push a stopper against one side of the nose-shaped protrusion so that one of the two claws is engaged with the tooth space of the ratchet wheel. When the operating handle is swung in one direction, one of the claws of the pawl pushes the ratchet wheel to rotate. On the contrary, when the operating handle is swung back, the nose-shaped protrusion presses the stopper into the long groove, so that the claw jumps on the teeth of the ratchet wheel and won't push the ratchet wheel to rotate reversely, thereby achieving the effect of unidirectional rotation of the ratchet wheel. When the operating handle is swung back, the stopper against the surface of the nose-shaped protrusion of the pawl is compressed and it has low resistance and rebounds back in height after being compressed, such that the first engaging pieces of the first sleeve unit and the second engaging pieces of the second sleeve unit are pressed against the first external thread of the first force output shaft and the second external thread of the second force output shaft to provide an anti-rotation effect. Thus, the ratchet wheel won't be pushed to rotate reversely when the operating handle is swung back.

Preferably, two sides of the ratchet wheel are concentrically formed with circular frames. The two sides of the ratchet wheel are pivoted to the force output end of the operating handle via the circular frames. The first force output shaft and the second force output shaft in the circular frames extend from both sides of the ratchet wheel to be out of the two sides of the force output end of the operating handle. The first external thread and the second external thread are screwed with the first nut and the second nut respectively via the largest number of screw threads, so as to increase the effective distance of the helical movement.

Preferably, the first pressure plate and the second pressure plate each have a through screw hole relative to the first force output shaft and the second force output shaft. The first nut and the second nut each have an annular coupling portion with an external thread relative to the through screw hole of the first pressure plate and the through screw hole of the second pressure plate. The coupling portion of the first nut is screwed and fixedly connected to the through screw hole of the first pressure plate by using a hydraulic press machine. The coupling portion of the second nut is screwed and fixedly connected to the through screw hole of the second pressure plate by using the hydraulic press machine. The first pressure plate and the second pressure plate can be concentrically, symmetrically extended away from each other or retracted toward each other.

Preferably, the first nut and the second nut each have a cylindrical surface. The first restraining member and the second restraining member are elastically deformable compression springs. The first sleeve unit is composed of a pair of first semicircular sleeves that are spliced to each other and correspond in diameter and in shape to the first nut. The second sleeve unit is composed of a pair of second semicircular sleeves that are spliced to each other and correspond in diameter and in shape to the second nut. The pair of first semicircular sleeves and the pair of second semicircular sleeves each have at least one slot to form at least one elastic frame side. The first L-shaped elastic plates extend from front edges of the elastic frame sides of the pair of first semicircular sleeves, respectively. The second L-shaped elastic plates extend from front edges of the elastic frame sides of the pair of second semicircular sleeves, respectively. The first restraining member and the second restraining member can be elastically expanded and deformed. The pair of first semicircular sleeves and the pair of second semicircular sleeves are deformed independently of each other, in cooperation with the elastic frame sides each having elastic deformation capacity. When the first external thread and the second external thread perform the helical movements, the first engaging pieces of the first L-shaped elastic plates and the second engaging pieces of the second L-shaped elastic plates react more quickly to the thrust of the helical movements to jump along the first and second external threads.

Preferably, the first nut and the second nut each have a groove around the surfaces of the first nut and the second nut. The pair of first semicircular sleeves and the pair of second semicircular sleeves each have at least one locking piece to be locked in the groove. Through the locking piece to be locked in the groove, the pair of first semicircular sleeves won't displace axially on the first nut. Through the locking piece to be locked in the groove, the pair of second semicircular sleeves won't displace axially on the second nut. When the first engaging pieces of the first L-shaped elastic plates and the second engaging pieces of the second L-shaped elastic plates are pressed against the first external thread and the second external thread to bear the pushing forces of the helical movements, they can jump along the first external thread and the second external thread, respectively.

Preferably, a front section of each of the first nut and the second nut is gradually tapered, so that a gap is defined between the elastic frame sides of the pair of first semicircular sleeves and the front section of the first nut as well as between the elastic frame sides of the pair of second semicircular sleeves and the front section of the second nut. Through the gap, the first restraining member is sleeved on part of the pair of first semicircular sleeves, and the second restraining member is sleeved on part of the pair of second semicircular sleeves. This can prevent the elastic frame side from being bound or pressed to affect its deformation.

Preferably, two first L-shaped elastic plates extend from each of the front edges of the elastic frame sides of the pair of first semicircular sleeves, and two second L-shaped elastic plates extend from each of the front edges of the elastic frame sides of the pair of second semicircular sleeves. The four first L-shaped elastic plates are spaced apart from each other around the first force output shaft. Preferably, the four first L-shaped elastic plates are spaced at equal intervals around the first force output shaft. The four second L-shaped elastic plates are spaced apart from each other around the second force output shaft. Preferably, the four second L-shaped elastic plates are spaced at equal intervals around the second force output shaft. The first engaging pieces of the four first L-shaped elastic plates are distributed in different positions of the roots and the crests of the first external thread in the helical movements. The second engaging pieces of the four second L-shaped elastic plates are distributed in different positions of the roots and the crests of the second external thread in the helical movement. When the first external thread and the second external thread perform the helical movements, each of the first engaging pieces and each of the second engaging pieces jump to pass through the crests of the first and second external threads at different timings, so that the helical movements won't be locked. When the operating handle is swung back, the first force output shaft and the second force output shaft won't be driven to rotate.

Preferably, the first external thread and the second external thread have the same pitch. The first engaging pieces of the first L-shaped elastic plates and the second engaging pieces of the second L-shaped elastic plates each correspond to the pitch and a depth of the first external thread and the second external thread and have a width that is 2 to 3 times the pitch and a thickness that is one quarter to one third of the pitch. The first engaging pieces and the second engaging pieces are square pieces and each have a bottom end extending downward about half to two-thirds of the depth of the first external thread and the second external thread. By setting the size conditions of the first engaging pieces and the second engaging pieces, the first engaging pieces and the second engaging pieces will not be excessively twisted and deformed when pushed by the first and second external threads.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIGS.3to18, a disc brake piston retraction tool20of the invention is shown. The tool20comprises a reversible ratchet wrench30, a first pressure plate assembly40, and a second pressure assembly50.

The reversible ratchet wrench30, as shown inFIG.4andFIG.5specifically, includes an operating handle31and a ratchet wheel32located at a force output end310of the operating handle31. A first force output shaft33and a second force output shaft34are disposed on both sides of the center of the ratchet wheel32and extend out of both sides of the force output end310of the operating handle31. The surface of the first force output shaft33is formed with a first external thread330, and the surface of the second force output shaft34is formed with a second external thread340. The first external thread330and the second external thread340are in different helical directions. Preferably, the first external thread330is a right-hand external thread, and the second external thread340is a left-hand external thread.

The first pressure plate assembly40, as shown inFIG.4,FIG.7andFIG.8specifically, includes a first pressure plate41, a first nut42, a first sleeve unit43, and a first restraining member44. The first pressure plate41has an outer surface410and an inner surface411. The first nut42is fixed to the inner surface411of the first pressure plate41relative to the first force output shaft33. The first nut42has a first internal screw hole420screwed with the first external thread330. The first sleeve unit43is made of an elastic material, and is sleeved on the outer surface of the first nut42. The front edge of one end of the first sleeve unit43has a plurality of first L-shaped elastic plates430that are arranged around the first internal screw hole420and extend toward the surface of the first force output shaft33. The first L-shaped elastic plates430each have a first engaging piece431corresponding to the first external thread330. The first engaging piece431is engagable in the root of the first external thread330. The width of the first engaging piece431is not more than 4 times the pitch of the first external thread330, and the thickness of the first engaging piece431is less than half of the pitch of the first external thread330. The first engaging piece431is configured to jump along the first external thread330to generate a pressing force. The first restraining member44is sleeved on the surface of the first sleeve unit43for restraining the first sleeve unit43on the first nut42.

The second pressure plate assembly50includes a second pressure plate51, a second nut52, a second sleeve unit53, and a second restraining member54. The second pressure plate51has an outer surface510and an inner surface511. The second nut52is fixed to the inner surface511of the second pressure plate51relative to the second force output shaft34. The second nut52has a second internal screw hole520screwed with the second external thread340. The second sleeve unit53is made of an elastic material, and is sleeved on the outer surface of the second nut52. The front edge of one end of the second sleeve unit53has a plurality of second L-shaped elastic plates530that are arranged around the second internal screw hole520and extend toward the surface of the second force output shaft34. The second L-shaped elastic plates530each have a second engaging piece531corresponding to the second external thread340. The second engaging piece531is engagable in the root of the second external thread340. The width of the second engaging piece531is not more than 4 times the pitch of the second external thread340, and the thickness of the second engaging piece531is less than half of the pitch of the second external thread340. The second engaging piece531is configured to jump along the second external thread340to generate a pressing force. The second restraining member54is sleeved on the surface of the second sleeve unit53for restraining the second sleeve unit53on the second nut52.

As shown inFIG.11,FIG.12andFIG.13specifically, when in use, the first pressure plate41and the second pressure plate51of the tool20are placed in an internal space61of a caliper housing60and located between at least one piston62that is not retracted and a fixed wall63. The force output direction of the reversible ratchet wrench30is selective (for example, the counterclockwise force is selected). The operating handle31of the reversible ratchet wrench30is pulled back and forth, and then the ratchet wheel32(rotated counterclockwise) drives the first force output shaft33and the second force output shaft34to rotate in one direction (counterclockwise). The helical movements of the first external thread330(right-hand external thread) and the second external thread340(left-hand external thread) act on the first internal screw hole420of the non-rotating first nut42and the second inner screw hole520of the non-rotating second nut52, such that the first pressure plate41and the second pressure plate51are driven to extend and move away from each other. The fixed wall63is configured to confine the movement of the first pressure plate41and the second pressure plate51and serves as a force support (the outer surface510of the second pressure plate51abuts against the fixed wall63to be supported), so that the piston62is retracted (by the outer surface410of the first pressure plate41) to the starting position in the cylinder.

As shown inFIG.15,FIG.16,FIG.17andFIG.18specifically, in the process of retracting the piston62, at least one of the first engaging pieces431of the first L-shaped elastic plates430of the first sleeve unit43and at least one of the second engaging pieces531of the second L-shaped elastic plates530of the second sleeve unit53are pressed against the first external thread330and the second external thread340to provide a damping force to limit rotation of the first force output shaft33and the second force output shaft34. Thus, when the operating handle31of the reversible ratchet wrench30is pulled back, it will not drive the ratchet wheel32, so that the tool20can be operated with one hand.

As shown inFIG.14,FIG.15,FIG.16andFIG.17specifically, when the operating handle31is operated, the helical movements of the first external thread330and the second external thread340drive the first pressure plate41and the second pressure plate51to extend and move away from each other. The first engaging pieces431of the first L-shaped elastic plates430and the second engaging pieces531of the second L-shaped elastic plates530are distributed in the roots and on the crests of the first external thread330and the second external thread340. The helical movements of the first external thread330and the second external thread340don't interfere with each other because the first engaging pieces431of the first L-shaped elastic plates430and the second engaging pieces531of the second L-shaped elastic plates530are configured to jump along the first external thread330and the second external thread340independently. The helical movements of the first external thread330and the second external thread340won't be locked, which improves the drive reliability.

According to the above embodiment, as shown inFIG.5andFIG.6specifically, the force output end30of the operating handle31has an accommodating hole311therein. The ratchet wheel32and a pawl35are pivotally connected in the accommodating hole311. The pawl35in the accommodating hole311is pivotally connected to the side edge of the ratchet wheel32via a pivot hole350. The pawl35has a pair of switching portions351that are disposed at both ends of the pivot hole350and extend out of the accommodating hole311. A nose-shaped protrusion352is formed on one side between the pair of switching portions351. Two spaced claws353A,353B each corresponding in shape to a tooth space320of the ratchet wheel32are formed on the other side between the pair of switching portions351. One side of the pawl35is provided with a spring36installed in a long groove312to push a stopper36(preferably a steel ball) against one side of the nose-shaped protrusion352, so that one of the two claws353A,353B is engaged with the tooth space320of the ratchet wheel32.

As shown inFIG.14specifically, when the operating handle31is swung in one direction (counterclockwise), the claw353A of the pawl35pushes the ratchet wheel32to rotate (counterclockwise). On the contrary, as shown inFIG.8specifically, when the operating handle31is swung back, the nose-shaped protrusion352presses the stopper37into the long groove312, so that the claw353A jumps on the teeth of the ratchet wheel32and won't push the ratchet wheel32to rotate reversely, thereby achieving the effect of unidirectional rotation of the ratchet wheel32.

As shown inFIG.16,FIG.17andFIG.18specifically, when the operating handle31is swung back, the stopper37against the surface of the nose-shaped protrusion352of the pawl35is compressed and it has low resistance and rebounds back in height after being compressed, such that the first engaging pieces431of the first sleeve unit43and the second engaging pieces531of the second sleeve unit53are pressed against the first external thread330of the first force output shaft33and the second external thread340of the second force output shaft34to provide an anti-rotation effect. Thus, the ratchet wheel32won't be pushed to rotate reversely when the operating handle31is swung back.

According to the above embodiment, as shown inFIG.4,FIG.5andFIG.8specifically, two sides of the ratchet wheel32are concentrically formed with circular frames321. The two sides of the ratchet wheel32are pivoted to the force output end310of the operating handle31via the circular frames321. The first force output shaft33and the second force output shaft34in the circular frames321extend from both sides of the ratchet wheel32to be out of the two sides of the force output end310of the operating handle31. The first external thread330and the second external thread340are screwed with the first nut42and the second nut52respectively via the largest number of screw threads, so as to increase the effective distance of the helical movement.

According to the above embodiment, as shown inFIG.4,FIG.7andFIG.8specifically, the first pressure plate41and the second pressure plate51each have a through screw hole412,512relative to the first force output shaft33and the second force output shaft34. The first nut42and the second nut52each have an annular coupling portion421,521with an external thread relative to the through screw hole412of the first pressure plate41and the through screw hole512of the second pressure plate51. The coupling portion421of the first nut42is screwed and fixedly connected to the through screw hole412of the first pressure plate41by using a hydraulic press machine, and the coupling portion521of the second nut52is screwed and fixedly connected to the through screw hole512of the second pressure plate51by using the hydraulic press machine. The first pressure plate41and the second pressure plate51can be concentrically, symmetrically extended away from each other or retracted toward each other.

According to the above embodiment, as shown inFIG.7,FIG.8,FIG.9andFIG.10specifically, the first nut42and the second nut52each have a cylindrical surface. Both the first restraining member44and the second restraining member54are elastically deformable compression springs. The first sleeve unit43is composed of a pair of first semicircular sleeves43A,43B that are spliced to each other and correspond in diameter and in shape to the first nut42. The second sleeve unit53is composed of a pair of second semicircular sleeves53A,53B that are spliced to each other and correspond in diameter and in shape to the second nut52. The pair of first semicircular sleeves43A,43B and the pair of second semicircular sleeves53A,53B each have at least one slot432,532to form at least one elastic frame side433,533. The first L-shaped elastic plates430extend from the front edges of the elastic frame sides433of the pair of first semicircular sleeves43A,43B, respectively. The second L-shaped elastic plates530extend from the front edges of the elastic frame sides533of the pair of second semicircular sleeves53A,53B, respectively.

As shown inFIG.7,FIG.15,FIG.16andFIG.17specifically, the first restraining member44and the second restraining member54can be elastically expanded and deformed. The pair of first semicircular sleeves43A,43B and the pair of second semicircular sleeves53A,53B are deformed independently of each other, in cooperation with the elastic frame sides433,533each having elastic deformation capacity. When the first external thread330and the second external thread340perform the helical movements, the first engaging pieces431of the first L-shaped elastic plates430and the second engaging pieces531of the second L-shaped elastic plates530react more quickly to the thrust of the helical movements to jump along the first and second external threads.

As shown inFIG.7andFIG.8specifically, the first nut42and the second nut52each have a groove422,522around the surfaces of the first nut42and the second nut52. The pair of first semicircular sleeves43A,43B and the pair of second semicircular sleeves53A,53B each have at least one locking piece434,534to be locked in the groove422,522. Through the locking piece434to be locked in the groove422, the pair of first semicircular sleeves43A,43B won't displace axially on the first nut42. Through the locking piece534to be locked in the groove522, the pair of second semicircular sleeves53A,53B won't displace axially on the second nut52.

As shown inFIG.15andFIG.16specifically, when the first engaging pieces431of the first L-shaped elastic plates430and the second engaging pieces531of the second L-shaped elastic plates530are pressed against the first external thread330and the second external thread340to bear the pushing forces of the helical movements, they can jump along the first external thread330and the second external thread340, respectively.

Preferably, as shown inFIG.7,FIG.8,FIG.9andFIG.10specifically, the front section of each of the first nut42and the second nut52is gradually tapered, so that a gap435,535is defined between the elastic frame sides433of the pair of first semicircular sleeves43A,43B and the front section of the first nut42as well as between the elastic frame sides533of the pair of second semicircular sleeves53A,53B and the front section of the second nut52. Through the gap435,535, the first restraining member44is sleeved on part of the pair of first semicircular sleeves43A,43B without the gap435, and the second restraining member54is sleeved on part of the pair of second semicircular sleeves53A,53B without the gap535. This can prevent the elastic frame side433,533from being bound or pressed to affect its deformation. Preferably, two first L-shaped elastic plates430extend from each of the front edges of the elastic frame sides433of the pair of first semicircular sleeves43A,43B, and two second L-shaped elastic plates530extend from each of the front edges of the elastic frame sides533of the pair of second semicircular sleeves53A,53B. The four first L-shaped elastic plates430are spaced apart from each other around the first force output shaft33. Preferably, the four first L-shaped elastic plates430are spaced at equal intervals (approximately 90 degrees to each other) around the first force output shaft33. The four second L-shaped elastic plates530are spaced apart from each other. Preferably, the four second L-shaped elastic plates530are spaced at equal intervals (approximately 90 degrees to each other) around the second force output shaft34.

As shown inFIG.15,FIG.16andFIG.17specifically, the first engaging pieces431of the four first L-shaped elastic plates430are distributed in different positions of the roots and the crests of the first external thread330in the helical movements. The second engaging pieces531of the four second L-shaped elastic plates530are distributed in different positions of the roots and the crests of the second external thread340in the helical movements. When the first external thread330and the second external thread340perform the helical movements, the first engaging pieces431and the second engaging pieces531react and bounce to pass through the crests of the first and second external threads at different timings, so that the helical movements won't be locked. When the operating handle31is swung back, the first force output shaft33and the second force output shaft34won't be driven to rotate.

According to the above embodiment, as shown inFIG.7,FIG.8,FIG.9andFIG.10specifically, the first external thread330and the second external thread340have the same pitch. The first engaging pieces431of the first L-shaped elastic plates430and the second engaging pieces531of the second L-shaped elastic plates530each correspond to the pitch and the depth of the first external thread330and the second external thread340and have a width that is 2 to 3 times the pitch and a thickness that is one quarter to one third of the pitch. The first engaging pieces431and the second engaging pieces531are square pieces and each have a bottom end extending downward about half to two-thirds of the depth of the first external thread330and the second external thread340. By setting the size conditions of the first engaging pieces431and the second engaging pieces531, as shown inFIG.15andFIG.16specifically, the first engaging pieces431and the second engaging pieces531will not be excessively twisted and deformed when pushed by the first and second external threads.