CN215334095U - Wedge block assembly of brake - Google Patents

Abstract

The utility model relates to the field of brakes and discloses a wedge block assembly of a brake, wherein a free stroke is integrated in a spiral piston at the top of a shell, a method that the free stroke of a traditional wedge block type expander is controlled through a gap between a piston and a piston sleeve is avoided, self-adjusting functions at two ends are integrated at the upper end of the shell, when an excessive gap exists between the brake and a brake drum, an automatic adjusting mechanism at the upper end detects the excessive gap, and then through transmission of a rectangular spline and a bevel gear, adjusting pairs at two ends are driven to be adjusted simultaneously, so that the adjusting quantity of a leading shoe and the adjusting quantity of a following shoe are consistent, and the eccentric wear phenomenon is avoided. The mode of controlling the free stroke by adopting the vertical axial displacement is adopted to control the gap between the brake drum and the brake shoe to be more stable, the eccentric wear is effectively reduced, and the occurrence of locking phenomenon caused by the eccentric wear is also reduced.

Description

Wedge block assembly of brake

Technical Field

The utility model relates to the technical field of brakes, in particular to a wedge block assembly of a brake.

Background

The wedge block expander of the traditional brake is easy to generate eccentric wear and locking phenomena in use, the eccentric wear of the wedge block expander is mainly caused by that a wedge brake belongs to an unbalanced brake, when a driver steps on a pedal plate, an air chamber is inflated for braking, according to theoretical calculation, in the braking process of the wedge brake, the efficiency factor of a leading shoe is about 2.6 times of that of the leading shoe, when the abrasion of a friction plate is assumed to be in direct proportion to the stress condition of the brake shoe, the abrasion degree of the friction plate of the leading shoe is about 2.6 times of that of the leading shoe, and because the adjusting mechanisms (the wedge expanders) of the wedge brake are controlled by single sides at the leading shoe end and the trailing shoe end, the self-adjusting mechanism at the leading shoe end is always in effect due to the abrasion of the leading shoe end. Due to the reasons, the wedge brake is easy to have eccentric wear during use. Because the push rod of the wedge type expander is not limited, when braking occurs, the push rod is easy to deflect and interfere with parts, so that the phenomenon of blocking is generated.

Therefore, how to provide a wedge assembly of a brake is a problem that needs to be solved by those skilled in the art.

SUMMERY OF THE UTILITY MODEL

Therefore, the utility model aims to provide a wedge block assembly of a brake, which solves the problem that the traditional wedge block expander is easy to have eccentric wear and locking phenomena.

The present invention provides a wedge assembly for a brake, comprising:

the device comprises a shell, a first pipeline and a second pipeline, wherein a vertical channel and a horizontal channel which are communicated with each other are vertically arranged in the shell; a first channel is formed at the top of the vertical channel, and a spiral piston sleeve is fixed in the first channel;

the rotary piston mechanism comprises a spiral piston, a rectangular spring and a rectangular spline shaft; the outer wall of the spiral piston is in threaded connection with the spiral piston sleeve, and the inner top of the spiral piston is limited with a pushing space; the rectangular spring is positioned in a space formed by the bottom of the spiral piston and the top of the rectangular spline shaft, the rectangular spring and the spiral piston rotate reversely or clockwise, and the synchronous rotation of the spiral piston and the rectangular spline shaft is realized in a reverse state; the bottom of the rectangular spline shaft is connected with a driving bevel gear;

the top end of the bottom push rod is connected with the top push rod and can move in a second channel formed by the spiral piston, the rectangular spring and the middle part of the rectangular spline shaft, and the bottom of the top push rod and the pushing space have a free stroke S; a wedge block is formed at the bottom of the bottom push rod, a support of a roller is sleeved at the wedge block, and the support moves in the through area of the horizontal channel and the vertical channel along with the bottom push rod;

the two auxiliary bevel gears are symmetrically arranged on two sides of the driving bevel gear, are meshed with the driving bevel gear and rotate in the horizontal channel;

two groups of adjusting pairs are arranged below the auxiliary bevel gear and are in gear transmission with the auxiliary bevel gear; the two groups of adjusting pairs are positioned on two sides of the bracket and are in contact with one group of rollers in a one-to-one correspondence manner;

and the limiting screw is inserted into the shell and then connected to the adjusting pair to limit the rotation of the adjusting pair.

According to the technical scheme, compared with the prior art, the utility model discloses the wedge block assembly of the brake, the free stroke is integrated into the spiral piston at the top of the shell, the method that the free stroke of the traditional wedge block type expander is controlled through the gap between the piston and the piston sleeve is avoided, the self-adjusting functions at the two ends are integrated at the upper end of the shell, when the brake and the brake drum have excessive gaps, the automatic adjusting mechanism at the upper end detects the excessive gaps, then the two end adjusting pairs are driven to be adjusted simultaneously through the transmission of the rectangular spline and the bevel gear, so that the adjusting quantity generated by the leading shoe and the trailing shoe is consistent, and the eccentric wear phenomenon is avoided. The mode of controlling the free stroke by adopting the vertical axial displacement is adopted to control the gap between the brake drum and the brake shoe to be more stable, the eccentric wear is effectively reduced, and the occurrence of locking phenomenon caused by the eccentric wear is also reduced.

Furthermore, the top of the top push rod is a columnar rod, the bottom of the top push rod is a push block with the diameter larger than that of the columnar rod, and the middle of the push block is provided with a thread groove connected with the bottom push rod.

Further, a top spring is sleeved on the top push rod, the top of the top push rod is connected with a butterfly-shaped gasket through a shaft by a snap spring, one end of the top spring is abutted against the butterfly-shaped gasket, and the other end of the top spring enters the first channel and is abutted against the top of the spiral piston sleeve T.

Furthermore, a stepped groove with a downward opening is formed at the bottom of the spiral piston, the first stepped groove is used for mounting the rectangular spring, and a first clamping groove is formed in the inner side wall of the second stepped groove; the rectangular spline shaft is characterized in that an upward matching groove is formed in the top of the rectangular spline shaft, the matching groove and the first step groove are installed in a matched mode to form the rectangular spring, a second clamping groove buckled with the first clamping groove is formed in the outer portion of the groove wall of the matching groove, and a square check ring is installed between the first clamping groove and the second clamping groove.

Furthermore, the rectangular spline shaft is sleeved with a bottom spring, one end of the bottom spring is abutted to the bottom of the matching ring groove, and the other end of the bottom spring is abutted to the top of the driving bevel gear.

Further, each secondary bevel gear comprises a wheel shaft, a secondary bevel gear body and a first straight gear; the wheel shaft is horizontally arranged in the horizontal channel, one end of the wheel shaft, which is close to the driving bevel gear, is provided with the auxiliary bevel gear body, one end of the wheel shaft, which is far away from the driving bevel gear, is provided with a hexagonal adjusting rod, and the hexagonal adjusting rod extends out of the horizontal channel and then plugs the horizontal channel through a screw cap; the first straight gear is arranged in the middle of the wheel shaft and is in transmission with the adjusting pinion.

Furthermore, each adjusting pair comprises an adjusting screw, a piston, a sliding block, a square clamp spring and a fixing clamping piece; a second spur gear meshed with the first spur gear is arranged on the outer wall of the piston, and the tooth width of the second spur gear is larger than that of the first spur gear; a horizontal thread groove in threaded connection with the adjusting screw is formed in the piston, one end of the adjusting screw extends out of the horizontal channel and is fixed through a fixing clamping piece, and the end part of the horizontal channel is blocked through a dust cover; the piston is connected with the sliding block through a square snap spring in the direction corresponding to the other end of the adjusting screw; the slider with the gyro wheel butt, just stop screw bottom with the slider is connected.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a schematic structural view of a wedge assembly of a brake provided by the present invention (in a state where a free stroke S exists);

FIG. 2 is a schematic view of a wedge assembly of the brake according to the present invention (with the free stroke S eliminated);

FIG. 3 is a perspective view of a wedge assembly of the brake provided by the present invention;

FIG. 4 is a perspective partial cross-sectional view of a wedge assembly of a brake provided in accordance with the present invention;

FIG. 5 is a schematic view showing a connection state of the bottom push rod, the bracket and the roller;

FIG. 6 is an exploded view of the rotary piston mechanism;

FIG. 7 is a cross-sectional view of the rotary piston mechanism;

FIG. 8 is a schematic view showing the connection state of the sub bevel gear, the adjusting pair and the driving bevel gear;

in the figure: 100-shell, 200-bottom push rod, 201-wedge, 202-roller, 203-bracket, 300-top push rod, 301-top spring, 302-shaft snap spring, 303-butterfly washer, 400-rotary piston mechanism, 401-spiral piston, 402-rectangular spring, 403-rectangular spline shaft, 404-driving bevel gear, 405-square retainer ring, 406-bottom spring, 500-auxiliary bevel gear, 501-wheel shaft, 502-auxiliary bevel gear body, 503-first straight gear, 504-hexagonal adjusting rod, 600-adjusting pair, 601-adjusting screw, 602-piston, 603-slider, 604-square snap spring, 605-fixing card, 606-second straight gear, 700-dust cover, 800-screw cover, 900-limit screw, T-spiral piston sleeve, S-free stroke.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the utility model and are not to be construed as limiting the utility model.

In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

Referring to fig. 1-8, an embodiment of the present invention discloses a wedge assembly for a brake, including: a housing 100, wherein a vertical channel and a horizontal channel which are communicated with each other are vertically arranged in the housing 100; a first channel is formed at the top of the vertical channel, and a spiral piston sleeve T is fixed in the first channel; a rotary piston mechanism 400, the rotary piston mechanism 400 including a spiral piston 401, a rectangular spring 402, and a rectangular spline shaft 403; the outer wall of the spiral piston 401 is in threaded connection with a spiral piston sleeve T, and the inner top of the spiral piston is limited with a pushing space; the rectangular spring 402 is positioned in a space formed by the bottom of the spiral piston 401 and the top of the rectangular spline shaft 403, the rectangular spring 402 and the spiral piston 401 reversely rotate or clockwise rotate, and the reverse rotation state realizes synchronous rotation of the spiral piston 401 and the rectangular spline shaft 403; the bottom of the rectangular spline shaft 403 is connected with a driving bevel gear 404; the push rod comprises a bottom push rod 200 and a top push rod 300, the top end of the bottom push rod 200 is connected with the top push rod 300 and can move in a second channel formed in the middle of a spiral piston 401, a rectangular spring 402 and a rectangular spline shaft 403, and the bottom of the top push rod 300 and a pushing space have a free stroke S; a wedge 201 is formed at the bottom of the bottom push rod 200, a bracket 203 of a roller 202 is sleeved at the wedge 201, and the bracket 203 moves in a through area of a horizontal channel and a vertical channel along with the bottom push rod 200; two auxiliary bevel gears 500 are symmetrically arranged at two sides of the driving bevel gear 404, are both meshed with the driving bevel gear 404 and rotate in the horizontal channel; two groups of adjusting pairs 600 are arranged below the auxiliary bevel gear 500 and are in gear transmission with the auxiliary bevel gear 500; the two groups of adjusting pairs 600 are positioned at two sides of the bracket 203 and are in contact with the group of rollers 202 in a one-to-one correspondence manner; and a limit screw 900, wherein the limit screw 900 is inserted into the housing 100 and then connected to the adjusting pair 600 to limit the rotation thereof.

The utility model discloses a wedge block assembly of a brake, wherein a free stroke is integrated in a spiral piston at the top of a shell, a method that the free stroke of a traditional wedge block type expander is controlled through a gap between the piston and a piston sleeve is avoided, self-adjusting functions at two ends are integrated at the upper end of the shell, when an excessive gap exists between the brake and a brake drum, an automatic adjusting mechanism at the upper end detects the excessive gap, then through transmission of a rectangular spline and a bevel gear, adjusting pairs at two ends are driven to be adjusted simultaneously, so that the adjusting amount of a leading shoe and a trailing shoe is consistent, and the eccentric wear phenomenon is avoided. The mode of controlling the free stroke by adopting the vertical axial displacement is adopted to control the gap between the brake drum and the brake shoe to be more stable, the eccentric wear is effectively reduced, and the occurrence of locking phenomenon caused by the eccentric wear is also reduced.

Advantageously, referring to fig. 1, the top push rod 300 has a cylindrical rod at the top, a smooth transition at the top, a push block with a diameter larger than that of the cylindrical rod at the bottom, and a threaded groove in the middle for connecting the bottom push rod 200. The thickness of the pushing block is smaller than the height value of the pushing space.

In the above embodiment, the top push rod 300 is sleeved with a top spring 301, the top of the top push rod 300 is connected to a butterfly gasket 303 through a shaft by a snap spring 302, one end of the top spring 301 abuts against the butterfly gasket 303, and the other end enters into the first channel and abuts against the top of the spiral piston sleeve T.

Advantageously, referring to fig. 4, 6 and 7, a stepped groove with a downward opening is formed at the bottom of the spiral piston 401, the first stepped groove is used for installing the rectangular spring 402, and a first clamping groove is formed on the inner side wall of the second stepped groove; the top of the rectangular spline shaft 403 is provided with an upward matching groove, a matching groove and a first step groove which are matched with each other to install a rectangular spring 402, the outer part of the groove wall of the matching groove is provided with a second clamping groove buckled with the first clamping groove, a square retainer ring 405 is installed between the first clamping groove and the second clamping groove, the rectangular spline shaft 403 is sleeved with a bottom spring 406, one end of the bottom spring 406 abuts against the bottom of the matching groove, and the other end of the bottom spring 406 abuts against the top of the active umbrella teeth 404.

The assembly grooves of the square check rings are designed in the spiral piston and the rectangular spline shaft, the square check rings are plugged into the first clamping grooves of the spiral piston during assembly, then the rectangular spline shaft with the rectangular spring is screwed into the spiral piston, the rear check rings can be clamped into the second clamping grooves of the rectangular spline shaft after assembly, and the spiral piston and the rectangular spline shaft can be prevented from being dragged away.

Referring to fig. 8, each secondary bevel gear 500 includes a hub 501, a secondary bevel body 502, a first straight gear 503; the wheel shaft 501 is horizontally arranged in the horizontal channel, an auxiliary bevel gear body 502 is arranged at one end of the wheel shaft, which is close to the driving bevel gear 404, a hexagonal adjusting rod 504 is formed at one end of the wheel shaft, which is far away from the driving bevel gear 404, and the horizontal channel is sealed by the screw cap 800 after the hexagonal adjusting rod 504 extends out of the horizontal channel; the first straight gear 503 is located in the middle of the wheel shaft 501 and is in gear transmission with the adjusting pair 600.

The hexagonal head adjusting rod is designed at the head of the auxiliary bevel gear, when the brake is clamped, the hexagonal head adjusting rod can be adjusted to withdraw the adjusted excessive clearance, and therefore the problem that the brake cannot be detached when clamped is solved.

Referring to fig. 1-4 and 8, each adjusting pair 600 includes an adjusting screw 601, a piston 602, a slider 603, a square clamp spring 604 and a fixing clip 605; the outer wall of the piston 602 is provided with a second spur gear 606 which is meshed with the first straight gear 503, and the tooth width of the second spur gear 606 is larger than that of the first straight gear 503; the piston 602 is internally provided with a horizontal thread groove in threaded connection with the adjusting screw 601, one end of the adjusting screw 601 extends out of the horizontal channel and is fixed by a fixing clamp plate 605, and the end part of the horizontal channel is blocked by a dust cover 700; the piston 602 is connected with a sliding block 603 through a square clamp spring 604 corresponding to the other end direction of the adjusting screw 601; the sliding block 603 is abutted against the roller 202, the bracket is sleeved on the bottom push rod, the roller is arranged on the bracket, the bottom push rod moves downwards, and the roller is opened towards two sides; and the bottom of the limit screw 900 is connected with the sliding block 603 to limit the rotation of the sliding block.

Bevel gear transmission angle is 90, and when there is excessive clearance, the screw piston takes place to rotate under the effect of piston sleeve, and screw piston mechanism is in contrary tooth relation, so the screw piston drives the rectangle spline and takes place to rotate, and then drives the main bevel gear of transferring and rotate, and then drives vice bevel gear and takes place to rotate, and vice bevel gear drives the piston and takes place to rotate, because adjusting bolt does not take place to rotate at the effect of card, L increase under this kind of condition, and then eliminates excessive clearance. The adjusting bolt afterbody has the fixed disk, is provided with a plurality of archs on the fixed disk, has a plurality ofly on the fixed card with the protruding complex notch of fixed disk.

Referring to fig. 1, the set free stroke S is eliminated: there is a certain gap (i.e. free stroke S) between the top push rod and the interior of the spiral piston, and when the driver steps on the pedal, the brake chamber is inflated to push the top push rod to move downward to push the gap, see fig. 2.

Eliminating excessive gaps: when excessive clearance exists between the brake drum and the brake, the brake air chamber pushes the top push rod to continuously move downwards, the top push rod and the spiral piston are eliminated, so that the spiral piston is driven to continuously move downwards, in the downward movement process, the spiral piston rotates under the action of the spiral piston sleeve, at the moment, the spiral piston and the rectangular spline belong to the contra-tooth direction (the consequent-tooth relation is that when the rotation directions of the spiral piston and the rectangular spring are the same, the rectangular spring begins to contract, and when the rotation directions of the spiral piston and the rectangular spring are opposite, the rectangular spring begins to expand and contacts with the inner wall of the spiral piston, at the moment, the rotation of the spiral piston is blocked and cannot rotate, so that the spiral piston is in the contra-tooth direction), the spiral piston drives the rectangular spline to rotate, and then the main bevel gear is driven to rotate, the auxiliary bevel gear is driven to rotate, and the bottom piston is driven to rotate through the auxiliary bevel gear, so that excessive gaps are eliminated.

Resetting the push rod: after braking is relieved, the brake air chamber is deflated, the top push rod returns under the action of the spring, and the spiral piston and the piston sleeve are in the tooth following direction, so that the gears do not rotate in the returning process.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the utility model. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples described in this specification can be combined and combined by those skilled in the art.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (7)

1. A wedge assembly for a brake, comprising:

the device comprises a shell (100), wherein a vertical channel and a horizontal channel which are communicated with each other are vertically arranged in the shell (100); a first channel is formed at the top of the vertical channel, and a spiral piston sleeve (T) is fixed in the first channel;

a rotary piston mechanism (400), the rotary piston mechanism (400) comprising a helical piston (401), a rectangular spring (402) and a rectangular spline shaft (403); the outer wall of the spiral piston (401) is in threaded connection with the spiral piston sleeve (T), and the inner top of the spiral piston is limited with a pushing space; the rectangular spring (402) is positioned in a space formed by the bottom of the spiral piston (401) and the top of the rectangular spline shaft (403), the rectangular spring (402) and the spiral piston (401) rotate reversely or clockwise, and the reverse rotation state realizes synchronous rotation of the spiral piston (401) and the rectangular spline shaft (403); the bottom of the rectangular spline shaft (403) is connected with a driving bevel gear (404);

the push rod comprises a bottom push rod (200) and a top push rod (300), the top end of the bottom push rod (200) is connected with the top push rod (300) and can move in a second channel formed in the middle of the spiral piston (401), the rectangular spring (402) and the rectangular spline shaft (403), and the bottom of the top push rod (300) and the pushing space have a free stroke S; a wedge block (201) is formed at the bottom of the bottom push rod (200), a bracket (203) of a roller (202) is sleeved at the wedge block (201), and the bracket (203) moves in the through area of the horizontal channel and the vertical channel along with the bottom push rod (200);

the two auxiliary bevel gears (500) are symmetrically arranged at two sides of the driving bevel gear (404), are meshed with the driving bevel gear (404) and rotate in the horizontal channel;

the two adjusting pairs (600) are positioned below the auxiliary bevel gear (500) and are in gear transmission with the auxiliary bevel gear (500); two groups of adjusting pairs (600) are positioned at two sides of the bracket (203) and are in contact with one group of rollers (202) in a one-to-one correspondence manner;

and the limiting screw (900), after being inserted into the shell (100), the limiting screw (900) is connected to the adjusting pair (600) to limit the rotation of the adjusting pair.

2. A wedge assembly of a brake as claimed in claim 1, wherein said top push rod (300) has a cylindrical rod at the top and a push block with a larger diameter than the cylindrical rod at the bottom, and said push block has a threaded groove at the middle for connecting said bottom push rod (200).

3. The wedge assembly of a kind of stopper according to claim 1, characterized by, the top push rod (300) is fitted with the top spring (301), the top of the top push rod (300) connects the butterfly shim (303) through the shaft with the snap spring (302), one end of the top spring (301) is abutted with the butterfly shim (303), the other end enters the first channel and is abutted against the top of the spiral piston sleeve (T).

4. The wedge block assembly of a kind of stopper according to claim 1, characterized by, the bottom of the said spiral piston (401) forms the downward open stepped groove, the first stepped groove is used for installing the said rectangular spring (402), the second stepped groove has first neck that offers on the inside wall; the top of the rectangular spline shaft (403) is provided with an upward matching groove, the matching groove is matched with the first step groove to install the rectangular spring (402), the outer part of the groove wall of the matching groove is provided with a second clamping groove buckled with the first clamping groove, and a square retainer ring (405) is installed between the first clamping groove and the second clamping groove.

5. A wedge assembly of a brake according to claim 4, characterized in that the rectangular spline shaft (403) is sleeved with a bottom spring (406), one end of the bottom spring (406) abuts against the bottom of the mating ring groove, and the other end abuts against the top of the active bevel gear (404).

6. A wedge assembly for a brake according to claim 1, wherein each of said secondary bevel gears (500) comprises an axle (501), a secondary bevel gear body (502), a first straight gear (503); the wheel shaft (501) is horizontally arranged in the horizontal channel, one end, close to the driving bevel gear (404), of the wheel shaft is provided with the auxiliary bevel gear body (502), one end, far away from the driving bevel gear (404), of the wheel shaft is provided with a hexagonal adjusting rod (504), and the hexagonal adjusting rod (504) extends out of the horizontal channel and then plugs the horizontal channel through a screw cap (800); the first straight gear (503) is arranged in the middle of the wheel shaft (501) and is in gear transmission with the adjusting pair (600).

7. A wedge assembly of a brake according to claim 6, wherein each of said adjustment pairs (600) comprises an adjustment screw (601), a piston (602), a slider (603), a square circlip (604) and a fixing clip (605); a second spur gear (606) meshed with the first spur gear (503) is arranged on the outer wall of the piston (602), and the tooth width of the second spur gear (606) is larger than that of the first spur gear (503); the piston (602) is internally provided with a horizontal thread groove in threaded connection with the adjusting screw (601), one end of the adjusting screw (601) extends out of the horizontal channel and is fixed by a fixing clamping sheet (605), and the end part of the horizontal channel is blocked by a dust cover (700); the piston (602) is connected with the sliding block (603) through a square clamp spring (604) in the direction corresponding to the other end of the adjusting screw (601); the sliding block (603) is abutted to the roller (202), and the bottom of the limiting screw (900) is connected with the sliding block (603).

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