Automobile brake gap rack type limit self-adjusting arm and adjusting method thereof

Abstract

The present application relates to the technical field of automobile braking, and provides a kind of automobile brake gap rack type limit self-adjusting arm and its adjusting method, including shell and the big worm, big worm gear, control disc, gear, rack and control sleeve arranged in shell, shell is provided with straight slot, rack is located in straight slot, big worm gear is engaged with big worm, control disc is fixedly connected with axle, upper half of rack is engaged with gear, the outer edge of control disc is provided with notch, control sleeve is elastically connected with rack, and the upstroke value of rack is limited by the upper stop of straight slot during braking, i.e. limited to the displacement value corresponding to Ce', instead of the current prevailing value of the displacement value corresponding to Ce of rack upstroke each time, the original extreme value adjustment method is replaced by the limit adjustment method of the case. To reduce or even avoid the problem of "dragging" or "locking" caused by "over-adjustment", to prevent traffic accidents.

Description

Technical Field

[0001] This invention relates to the field of automotive braking technology, specifically to a rack-and-pinion self-adjusting arm for automotive brake clearance and its adjustment method. Background Technology

[0002] A car's drum brake works by pressing and releasing the brake shoes (including friction blocks) against the brake drum on the wheel. When the brakes are released, there is a pre-existing gap ζ between the brake drum and the brake shoes to allow the car to move normally. This gap can increase due to wear of the brake shoe friction blocks and thermal expansion of other components, leading to a longer stroke of the brake chamber pushrod, reduced thrust, and consequently, brake lag and reduced braking force.

[0003] The self-adjusting arm is a device installed on a car to record the excess clearance angle (Ce) caused by friction block wear, and can adjust the brake clearance to the normal allowable clearance (ζ).

[0004] There is a pre-set gap ζ between the hoof and drum, and a corresponding pre-set gap angle C for the self-adjusting arm. Existing self-adjusting arms can gradually reduce the excess gap β. β is very large when hot, and after multiple reductions, the hoof-drum gap approaches ζ. The actual gap angle Q of the self-adjusting arm approaches the pre-set gap angle C. When the vehicle is parked or has cooled down, the hoof-drum gap may become smaller than the pre-set gap ζ, a phenomenon known in the industry as "over-adjustment." Over-adjustment is caused by physical factors such as thermal expansion and is unavoidable. Severe over-adjustment can lead to "driving" or even "locking up," causing traffic accidents.

[0005] Currently, all types of self-adjusting brake arms worldwide operate on the same principle: as the brake drum clearance increases, the self-adjusting arm angle also increases, with Ce serving as the adjustment basis during the return stroke. The adjustment amount Y increases with Ce, i.e., Y = fCe, where f is a fixed proportionality coefficient, and Y is a function of the excess clearance angle Ce. The industry aims to reduce the amount of adjustment per cycle, but due to structural limitations, the proportionality coefficient f cannot be made very small, and Ce is a random variable that cannot be controlled. Higher brake drum temperatures result in a larger Ce, leading to a greater adjustment amount Y and a higher likelihood of over-adjustment after cooling. Recognizing this reality, a consensus was reached over thirty years ago internationally that over-adjustment is caused by physical factors. Since it cannot be avoided, drivers must rely on experience to manually increase the clearance to the pre-set value. This self-adjusting arm adjustment method based on Y = fCe is called the extreme value method. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to reduce the occurrence of "over-adjustment" of the self-adjusting arm, so as to avoid the possibility of "dragging" or even "locking up" of the car, which could lead to traffic accidents.

[0007] To address the aforementioned technical problems, this invention provides a rack-and-pinion self-adjusting arm for automotive brake clearance, comprising a housing and a large worm gear, a large worm wheel, a control disc, a gear, a rack, and a control sleeve disposed within the housing. The housing has a straight groove, within which the rack is located. The large worm wheel meshes with the large worm gear. The control disc is fixedly connected to the axle. The upper half of the rack meshes with the gear. A notch is provided on the outer edge of the control disc. The control sleeve is elastically connected to the rack. A protrusion is provided on the circumferential surface of the control sleeve, located within the notch. The angle A corresponding to the notch is equal to the sum of the angle B corresponding to the protrusion and the reserved clearance angle C. The length of the straight groove is greater than the length of the rack, and the difference between the length of the straight groove and the length of the rack is greater than the sum of the clearances of all transmission components, but much smaller than the displacement value corresponding to the excess clearance angle Ce.

[0008] This invention provides a method for adjusting a rack-and-pinion self-adjusting arm for limiting automotive brake clearance, comprising the following aspects:

[0009] Gap adjustment strategy

[0010] The excess clearance angle Ce is decomposed into Ce′+D, i.e., Ce=Ce′+D, where Ce′ is a "limited angle". Under the premise of the same type of vehicle and the same type of adjusting arm, the value of Ce′ is fixed. However, it will vary depending on the type and specification of the vehicle or the adjusting arm. The range of Ce′ is: it must be much smaller than Ce, but larger than the "minimum adjustment starting amount". The "minimum adjustment amount" is the sum of the clearances between all transmission components. Only when the rotation angle of the self-adjusting arm is slightly greater than the minimum adjustment starting amount can the mechanism complete the adjustment action.

[0011] Ce′ is used to replace Ce as the stroke value for each upward movement of the rack and the adjustment basis for each return stroke, while D is not involved in the adjustment, so as to obtain the ideal smaller adjustment amount: Y′=fCe′, so Y′ is much smaller than Y; at the same time, after the self-adjusting arm rotates past Ce′ during braking, it can still rotate past D even if the rack cannot move upward, so that the drum can both make contact and complete braking during braking, and limit the stroke value of the rack during each braking to the displacement value corresponding to Ce′.

[0012] After the self-adjusting arm is installed, its initial state is that it is deviated to the right by an angle C from the vertical line of the S-camshaft, and the centerline of the self-adjusting arm coincides with the 0° reference line.

[0013] When the car needs to brake, the driver presses the brake pedal. The brake chamber push rod pushes the self-adjusting arm to rotate counterclockwise around the center of the control disc. The control disc is fixed to the car body and remains stationary, becoming the center of rotation of the self-adjusting arm. At this time, there are two situations:

[0014] 1. If the actual gap of the hoof drum is less than or equal to the reserved gap ζ, then the actual rotation angle of the self-adjusting arm is less than or equal to the reserved gap angle C. When the self-adjusting arm, along with the rack and control sleeve, rotates counterclockwise by an angle less than or equal to the reserved gap C, after completing the rotation action as described above, the bottom of the protrusion on the control sleeve will not touch the lower edge of the notch on the control plate, so the rack will not move up and the hoof drum gap will not be adjusted during the return stroke.

[0015] 2. If the actual gap between the drum and the hoof is greater than the reserved gap ζ, and correspondingly, the actual rotation angle of the self-adjusting arm is greater than the reserved gap angle C, the adjustment mechanism of the self-adjusting arm will reduce the gap between the drum and the hoof. The process is as follows:

[0016] ① Record the basis for adjustment during braking:

[0017] Step 1: When the driver presses the brake pedal, the self-adjusting arm rotates counterclockwise. When it rotates past the reserved clearance angle C, the central axis of the self-adjusting arm coincides with the last edge of angle C, and the brake shoes open. Since the actual clearance between the brake shoes and drum is greater than the reserved clearance ζ, the brake shoes and brake drum do not make complete contact. While the self-adjusting arm rotates counterclockwise, it drives the rack and control sleeve to rotate counterclockwise by a reserved clearance angle C. After completing the rotation action as described above, the top of the protrusion on the control sleeve leaves the upper edge of the notch, and the bottom touches the lower edge of the notch.

[0018] Step 2: The self-adjusting arm continues to rotate counterclockwise. When it passes angle Ce′, the central axis of the self-adjusting arm coincides with the last edge of angle Ce′. The lower edge of the control disc notch pushes the control sleeve and rack upward together. During the upward movement, the rack drives the gear to rotate freely in the clockwise direction on the one-way clutch. Then, the rack is blocked by the upper stop of the straight groove, and the rack cannot continue to move upward. During this process, the upward stroke of the rack is equal to the displacement value corresponding to Ce′. Thus, the gear rotates freely through the angle corresponding to Ce′. At this time, the brake shoe and brake drum are not yet in complete contact. During the return stroke, the gear and the one-way clutch are wedged together and reverse in the opposite direction. The reverse rotation value is the same as the free rotation value. Therefore, Ce′ is the basis for adjusting the clearance during the return stroke.

[0019] Step 3: The self-adjusting arm continues to rotate counterclockwise. When it rotates past the difference D between Ce and Ce′, the central axis of the self-adjusting arm coincides with the last edge of angle D. Since the rack is blocked by the upper stop of the straight groove, it cannot continue to move upward. Because the control sleeve and the rack are connected by a spring, the control plate can still compress the return spring and push the control sleeve to continue moving on its own. Since the large worm gear is separated from the one-way clutch, the torque of the S-camshaft increases rapidly, and the friction block of the brake shoe presses against the brake drum. The total rotation angle of the self-adjusting arm reaches the value of the excess clearance angle Ce. At this time, the brake shoe and the brake drum are in complete contact.

[0020] ② During the braking process, adjust the shoe-drum clearance to be smaller according to the rack movement value recorded during braking.

[0021] Step 4: When the driver releases the brake pedal, the self-adjusting arm rotates clockwise. When it rotates through angle D, the control sleeve resets under the action of the return spring, and the protrusion returns to the lower edge of the control disc notch, with the protrusion and the middle protrusion flush.

[0022] Step 5: The self-adjusting arm continues to rotate clockwise. When it passes C, the protrusion and the middle protrusion contact the upper edge of the notch.

[0023] Step 6: The self-adjusting arm continues to rotate clockwise. When it passes Ce′, the rack and control sleeve are pressed down to their original positions by the upper edge of the notch. During the process of the rack moving down to reset, the gear and clutch spring reverse and rotate together, driving the large worm to rotate, which in turn drives the large worm wheel to rotate, and then drives the S-camshaft connected to the spline center of the large worm wheel to rotate counterclockwise, so that the brake clearance is adjusted by a small amount, Y′=fCe′. We call this adjustment method the limit method.

[0024] The technical solution of the present invention has the following beneficial effects:

[0025] This invention provides a rack-and-pinion self-adjusting arm for limiting brake clearance in automobiles and its adjustment method. The method replaces the original extreme value adjustment method with a limit adjustment method, decomposing the excess clearance angle Ce into Ce′+D, i.e., Ce=Ce′+D. During braking, the upper stop of the straight groove limits the upward travel value of the rack each time, i.e., it is limited to the displacement value corresponding to Ce′. This replaces the current common method where the upward movement of the rack during each braking is the displacement value corresponding to Ce. Therefore, upon each brake release, the brake shoe clearance is automatically adjusted, Y′=fCe′, making Y′ much smaller than Y. Thus, when the brake drum is hot, the clearance will not be adjusted to be less than the reserved clearance ζ. Since the rack and control sleeve are elastically connected by a spring, the compression of the spring can compensate for the rotation angle D, allowing the self-adjusting arm to rotate past Ce′ and then past D without pushing the rack upward, achieving complete contact between the brake drum and brake shoe to complete the braking action. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a first-view exploded view of a rack-and-pinion self-adjusting arm for limiting the braking clearance of an automobile according to the present invention.

[0028] Figure 2This is a second-view exploded view of a rack-and-pinion self-adjusting arm for limiting the braking clearance of an automobile, according to the present invention.

[0029] Figure 3 This is a schematic diagram of the self-adjusting arm of the present invention without its housing;

[0030] Figure 4 This is a perspective sectional view of the self-adjusting arm of the present invention after the housing has been removed;

[0031] Figure 5 This is a planar perspective view of the self-adjusting arm of the present invention;

[0032] Figure 6 This is a perspective view of the connection between the control sleeve and the rack of the present invention;

[0033] Figure 7 This is a cross-sectional view of the connection between the control sleeve and the rack of the present invention;

[0034] Figure 8 This is a cross-sectional view of the control sleeve of the present invention installed inside the housing;

[0035] Figure 9 This is a schematic diagram showing the initial state of the self-adjusting arm and the corresponding state of the drum.

[0036] Figure 10 This is a schematic diagram of the self-adjusting arm rotating through the reserved clearance angle C during vehicle braking.

[0037] Figure 11 This is a schematic diagram of the self-adjusting arm rotating through angle C+Ce′ during vehicle braking according to the present invention;

[0038] Figure 12 This is a schematic diagram of the self-adjusting arm rotating through angle C+Ce′+D during vehicle braking according to the present invention;

[0039] Figure 13 This is a schematic diagram of the present invention when the vehicle rotates through point D during the return stroke after the brake is released;

[0040] Figure 14 This is a schematic diagram of the present invention when the car rotates through C+D during the return stroke after the brake is released;

[0041] Figure 15 This is a schematic diagram of the present invention when the car rotates through C+D+Ce′ during the return stroke after the brake is released.

[0042] 1. Housing; 2. Large worm gear; 3. Large worm wheel; 4. Control panel; 41. Notch; 5. Gear; 6. Rack; 61. Upper boss; 62. Lower boss; 63. Middle boss; 7. Straight groove; 8. Control sleeve; 81. Protrusion; 9. Positioning rod; 10. Return spring; 11. Clutch spring; 12. Coil spring; 13. One-way clutch; 14. S-camshaft; 15. Brake shoe; 16. Brake drum; 17. Positioning spring; 18. Partition wall. Detailed Implementation

[0043] The technical solution of the present invention will now be described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of, and not all of, the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0044] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0045] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0046] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0047] like Figure 1-5As shown, this invention provides a rack-and-pinion self-adjusting arm for limiting automotive brake clearance, comprising a housing 1 and a large worm gear 2, a large worm wheel 3, a control disc 4, a gear 5, a rack 6, and a control sleeve 8 disposed within the housing 1. The housing 1 has a straight groove 7, and the rack 6 is located within the straight groove 7. The large worm wheel 3 meshes with the large worm gear 2. The control disc 4 is fixedly connected to the axle. The upper half of the rack 6 meshes with the gear 5. The outer edge of the control disc 4 has a notch 41. The control sleeve 8 is elastically connected to the rack 6. The circumferential surface of the control sleeve 8 has a protrusion 81 located within the notch 41. The angle value of the central angle A corresponding to the notch 41 is equal to the sum of the angle value of the central angle B corresponding to the protrusion 81 and the angle value of the reserved clearance angle C. The length value of the straight groove 7 is greater than the length value of the rack 6. The difference between the length of the straight groove 7 and the length of the rack 6 is greater than the displacement value corresponding to the sum of the clearances of all transmission components, and much smaller than the displacement value corresponding to the excess clearance angle Ce, i.e., equal to the displacement value corresponding to Ce′. All transmission components refer to the aforementioned large worm gear 2, large worm wheel 3, control panel 4, gear 5, rack 6, and control sleeve 8.

[0048] The length of the straight groove 7 is greater than the length of the rack 6 by a length corresponding to Ce′.

[0049] like Figure 6-8 As shown, the rack 6 and the control sleeve 8 are elastically connected in the following way: the control sleeve 8, the return spring 10, the positioning spring 17, and the positioning rod 9 are together engaged between the upper boss 61 and the lower boss 62 of the rack 6. The head of the positioning rod 9 rests in the corresponding recess in the housing 1, and the positioning spring 17 stabilizes the rack 6 at the bottom of the straight groove 7 of the housing 1.

[0050] When an external force is applied to the bottom of the control sleeve 8, the control sleeve 8 will move axially upward along with the rack 6. When the rack 6 is restricted, it can compress the return spring 10 and continue to move upward to the working position on its own. When the external force on the control sleeve 8 is removed, the return spring 10 returns to its original position, causing the control sleeve 8 to reset and move downward.

[0051] This invention provides a method for adjusting a rack-and-pinion self-adjusting arm for limiting automotive brake clearance, comprising the following aspects:

[0052] Gap adjustment strategy

[0053] The excess clearance angle Ce is decomposed into Ce′+D, i.e., Ce=Ce′+D, where Ce′ is a "limited angle." Under the premise of the same type of vehicle and the same type of adjusting arm, the value of Ce′ is fixed. However, it will vary depending on the type and specification of the vehicle or the adjusting arm. The range of Ce′ values ​​is: much smaller than Ce, but larger than the "minimum adjustment starting amount," where the "minimum adjustment amount" is the sum of the clearances between all transmission components. The mechanism can only complete the adjustment action when the rotation angle is slightly greater than the minimum adjustment starting amount. Therefore, the smaller the value of Ce′, the better, but it needs to be greater than the "minimum adjustment starting amount" because if Ce′ is less than the minimum adjustment starting amount, the adjusting mechanism will not operate.

[0054] For example, if the excess clearance angle is 10°, decompose 10° into 1.5° + 8.5°, adjust only 1.5° each time, and do not adjust the remaining 8.5°.

[0055] Ce′ is used instead of Ce as the stroke value for each upward movement of rack 6 and the adjustment basis for each return stroke, while D is not involved in the adjustment, so as to obtain the ideal smaller adjustment amount: Y′=fCe′, so Y′ is much smaller than Y; at the same time, after the self-adjusting arm rotates past Ce′ during braking, it can still rotate past D even if rack 6 no longer moves upward, so that the drum can both make contact and complete braking during braking, and limit the stroke value of rack 6 to the displacement value corresponding to Ce′ during each braking.

[0056] like Figure 9 As shown, after the self-adjusting arm is installed, its initial state is that it is deviated to the right by an angle C from the vertical line of the S-camshaft 14, and the centerline of the self-adjusting arm coincides with the 0° reference line.

[0057] When the car needs to brake, the driver presses the brake pedal. The brake chamber push rod pushes the self-adjusting arm to rotate counterclockwise around the center of control disc 4. Control disc 4 is fixed to the car body and becomes the rotation center of the self-adjusting arm. At this time, there are two situations:

[0058] 1. If the actual gap of the hoof drum is less than or equal to the reserved gap ζ, then the actual rotation angle of the self-adjusting arm is less than or equal to the reserved gap angle C. When the self-adjusting arm rotates counterclockwise, it will rotate the rack 6 and the control sleeve 8 together counterclockwise by an angle less than or equal to the reserved gap C. After the rotation action is completed according to the above situation, the bottom of the protrusion 81 on the control sleeve 8 will not touch the lower edge of the notch 41 of the control disk 4, so the rack 6 will not move up and will not adjust the gap of the hoof drum during the return stroke.

[0059] 2. If the actual gap between the drum and the hoof is greater than the reserved gap ζ, and correspondingly, the actual rotation angle of the self-adjusting arm is greater than the reserved gap angle C, the adjustment mechanism of the self-adjusting arm will reduce the gap between the drum and the hoof. The reduction process is as follows:

[0060] ① Record the basis for adjustment during braking:

[0061] Step 1: As Figure 10 As shown, when the driver presses the brake pedal, the self-adjusting arm rotates counterclockwise. When it rotates past the reserved clearance angle C, the central axis of the self-adjusting arm coincides with the last edge of angle C, and the brake shoe 15 opens accordingly. Since the actual clearance of the shoe drum is greater than the reserved clearance ζ, the brake shoe 15 and the brake drum 16 do not make complete contact. While the self-adjusting arm rotates counterclockwise, it drives the rack 6 and the control sleeve 8 to rotate counterclockwise by a reserved clearance angle C. After completing the rotation action as described above, the top of the protrusion 81 on the control sleeve 8 leaves the upper edge of the notch 41, and the bottom abuts against the lower edge of the notch 41.

[0062] Step 2: As Figure 11 As shown, the self-adjusting arm continues to rotate counterclockwise. When it rotates through angle Ce′, the central axis of the self-adjusting arm coincides with the last edge of angle Ce′. The lower edge of the notch 41 of the control disc 4 pushes the control sleeve 8 and rack 6 upward together. During the upward movement, rack 6 drives gear 5 to rotate freely in the forward direction. Then rack 6 is blocked by the upper stop of the straight groove 7, and rack 6 cannot continue to move upward. During this process, the stroke value of rack 6 is equal to the displacement value corresponding to Ce′. Thus, gear 5 rotates freely through the angle corresponding to Ce′. At this time, brake shoe 15 and brake drum 16 have not yet fully contacted. During the return stroke, gear 5 is wedged into one-way clutch 13 and then rotates in reverse. The reverse rotation value is the same as the free rotation value. Therefore, Ce′ is the basis for adjusting the clearance during the return stroke.

[0063] Step 3: As Figure 12 As shown, the self-adjusting arm continues to rotate counterclockwise. When it rotates past the difference D between Ce and Ce′, the central axis of the self-adjusting arm coincides with the last edge of angle D. Because the rack 6 is blocked by the upper stop of the straight groove 7, it cannot move upwards further. Since the control sleeve 8 and the rack 6 are elastically connected by the return spring 10, the control disc 4 can still compress the return spring 10 and push the control sleeve 8 to continue moving independently. As the large worm gear 2 separates from the one-way clutch 13, the torque of the S-camshaft 14 increases rapidly, and the friction block of the brake shoe 15 presses against the brake drum 16. The total rotation angle of the self-adjusting arm reaches the value of the excess clearance angle Ce. At this time, the brake shoe 15 and the brake drum 16 are in complete contact. The subsequent elastic deformation of the brake drum is not analyzed in this invention.

[0064] The above steps limit the upward stroke of rack 6 during braking by using the upper stop of straight groove 7, i.e., limiting it to the displacement value corresponding to Ce′. This replaces the current practice where the upward stroke of rack 6 during each braking stroke is the displacement value corresponding to Ce. This makes Y′ much smaller than Y, so the clearance will not be adjusted to be very small when hot, thus reducing the occurrence of "over-adjustment". The compression energy of return spring 10 compensates for the rotation angle of D, allowing the self-adjusting arm to rotate past Ce′ and then rotate past D without pushing rack 6 upward, so as to achieve complete contact between brake drum 16 and brake shoe 15 and complete the braking action.

[0065] ② During the braking process, adjust the drum-hoof gap to a smaller value according to the upward movement of rack 6 recorded during braking (assuming that the elastic deformation has been released, return to the end of step 3 above).

[0066] Step 4: As Figure 13 As shown, after the driver releases the brake pedal, the self-adjusting arm rotates clockwise. When it rotates through angle D, the control sleeve 8 is reset under the action of the return spring 10, and the protrusion 81 returns to the lower edge of the notch 41 of the control disc 4. The protrusion 81 and the middle protrusion 63 are flush.

[0067] Step 5: As Figure 14 As shown, the self-adjusting arm continues to rotate clockwise. When it passes C, the protrusion 81 and the intermediate protrusion 63 contact the upper edge of the notch 41.

[0068] Step 6: As Figure 15 As shown, the self-adjusting arm continues to rotate clockwise. When it passes Ce′, the rack 6 and the control sleeve 8 are pressed down to their original positions by the upper edge of the notch 41. During the process of the rack 6 moving down to reset, the gear 5 and the clutch spring 11 reverse and rotate together, driving the large worm 2 to rotate, thereby driving the large worm wheel 3 to rotate, and then driving the S-camshaft 14, which is splined to the center of the large worm wheel 3, to rotate counterclockwise, so that the brake clearance is adjusted by a small amount, Y′=fCe′. We call this adjustment method the limit method.

[0069] After each braking operation, the shoe drum clearance is reduced during the return stroke by an adjustment amount of Y′. This process is repeated multiple times until the excess shoe drum clearance is gradually reduced, making the rotation angle of the adjusting arm close to C+Ce′.

[0070] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A rack-and-pinion self-adjusting arm for limiting the braking clearance of an automobile, comprising a housing (1) and a large worm gear (2), a large worm wheel (3), a control disc (4), a gear (5), and a rack (6) disposed within the housing (1), wherein the housing (1) has a straight groove (7), the rack (6) is located within the straight groove (7), the large worm wheel (3) meshes with the large worm gear (2), the control disc (4) is fixedly connected to the axle, the upper half of the rack (6) meshes with the gear (5), the outer edge of the control disc (4) has a notch (41), and the length of the straight groove (7) is greater than the length of the rack (6), characterized in that, It also includes a control sleeve (8), which is elastically connected to the rack (6). The control sleeve (8) has a protrusion (81) on its circumferential surface. The protrusion (81) is located in the notch (41). The angle value of the central angle A corresponding to the notch (41) is equal to the sum of the angle value of the central angle B corresponding to the protrusion (81) and the angle value of the reserved gap angle C. The difference between the length of the straight groove (7) and the length of the rack (6) is greater than the sum of the gaps of all transmission components and much smaller than the displacement value corresponding to the excess gap angle Ce. The control sleeve (8), return spring (10), positioning spring (17) and positioning rod (9) are together locked between the upper boss (61) and the lower boss (62) of the rack (6).

2. The method for adjusting a rack-and-pinion self-adjusting arm for limiting automotive brake clearance as described in claim 1, characterized in that, The process includes the following: After the self-adjusting arm is installed, its initial state is that it is deviated to the right by an angle C from the vertical line of the S-camshaft (14), and the centerline of the self-adjusting arm coincides with the 0° reference line. I. Basis for recording and adjusting during braking: Step 1: When the driver presses the brake pedal, the self-adjusting arm rotates counterclockwise. When it rotates past the reserved gap angle C, the central axis of the self-adjusting arm coincides with the last edge of angle C. While the self-adjusting arm rotates counterclockwise, it drives the rack (6) and the control sleeve (8) to rotate counterclockwise together by a reserved gap angle C. After the control sleeve (8) completes the rotation action as described above, the top of the protrusion (81) on the control sleeve (8) leaves the upper edge of the notch (41), and the bottom touches the lower edge of the notch (41). Step 2: The self-adjusting arm continues to rotate counterclockwise. When it rotates through the angle Ce', the central axis of the self-adjusting arm coincides with the last edge of the angle Ce'. The lower edge of the notch (41) of the control disk (4) pushes the control sleeve (8) and the rack (6) to move upward together. Then the rack (6) is blocked by the upper stop of the straight groove (7), and the rack (6) cannot continue to move upward. During this process, the stroke value of the rack (6) is equal to the displacement value corresponding to Ce'. Thus, the gear (5) rotates through the angle corresponding to Ce'. At this time, the brake shoe (15) and the brake drum (16) have not yet fully contacted. Step 3: The self-adjusting arm continues to rotate counterclockwise. When it rotates past the difference D between Ce and Ce', the central axis of the self-adjusting arm coincides with the last edge of angle D. Since the rack (6) has been blocked by the upper stop of the straight groove (7), it cannot continue to move upward. The control plate (4) compresses the return spring (10) and pushes the control sleeve (8) to continue moving. The friction block of the brake shoe (15) presses against the brake drum (16). The total rotation angle of the self-adjusting arm reaches the value of the excess clearance angle Ce. At this time, the brake shoe (15) and the brake drum (16) are in complete contact.

2. During the braking process, adjust the shoe drum clearance to be smaller according to the upward displacement value of rack (6) recorded during the braking process: Step 4: After the driver releases the brake pedal, the self-adjusting arm rotates clockwise. When it rotates through angle D, the return spring (10) resets, and the protrusion (81) of the control sleeve (8) returns to the lower edge of the notch (41) of the control plate (4), and the middle boss (63) of the protrusion (81) and the rack (6) are also reset. Level; Step 5: The self-adjusting arm continues to rotate clockwise. When it passes C, the protrusion (81) and the intermediate protrusion (63) contact the upper edge of the notch (41); Step 6: The self-adjusting arm continues to rotate clockwise. When it passes Ce', the rack (6) and control sleeve (8) are pressed down to their original positions by the upper edge of the notch (41). During the process of the rack (6) moving down to reset, it drives the gear (5) to rotate in reverse. The gear (5) and clutch spring (11) are wedged in the opposite direction, and then the large worm gear (2) rotates, thereby driving the large worm wheel (3) to rotate, which in turn drives the S-camshaft (14) connected to the spline of the large worm wheel (3) to rotate counterclockwise, and the clearance is adjusted once.

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