DESC:FIELD OF INVENTION
[0001] The present invention relates to a braking system of an automobile, and more particularly to a disc braking system for the automobile.
BACKGROUND OF THE INVENTION
[0002] Vehicles, especially two and three-wheeled vehicles are known to possess different types of braking mechanisms, such as a drum brake, disc brake etc. Disc brakes known in the art have many associated advantages. For example, disc brakes can be inspected without removing wheels, thus making the maintenance of such brakes, less cumbersome. Because of its lower disc inertia, the braking torque can be less in case of disc brake, thus achieving shorter braking distance for the same force. Brake actuation feel and modulation are improved in case of disc brakes as compared to a drum brake.
[0003] Further, in case of drum brakes, loss of braking forces due to wear of brake shoes is higher. Furthermore, efficiency of braking system is low in case of vehicles using drum brake as compared to a vehicle using disc brakes, in spite of the fact that the overall cost of the vehicle using drum brake is relatively low as compared to the vehicle using disc brakes.
[0004] . Typically, a drum brake operated by a brake actuating member, includes a brake panel mounted on axle in close proximity to the wheel hub. The brake panel includes one or more brake shoes. Each of the brake shoes is provided with a brake lining. The brake shoes contact the inner surface of the wheel hub when the rider operates the brake actuating member in order to decelerate the vehicle and eventually resulting in bringing the vehicle to halt. Once the rider releases the brake actuating member, the brake shoes go out of contact from the wheel hub allowing the vehicle to move.
[0005] During the course of operation, the brake lining on the brake shoes tends to wear out. The wearing of the brake lining may be due to one or more reasons such as irregular braking patterns, rough braking, quality of brake lining, life of lining material, and so on.. Wear of the brake lining in turn reduces the braking ability of the vehicle. It also reduces the rider comfort as the brake actuating member free play increases beyond a threshold limit, which may force the rider to apply more braking force to bring the vehicle to halt.
[0006] On the other hand, disc brakes include a pair of brake pads, which on actuation come closer to the disc and causes retardation of the rotating disc(s). Typically, the brake pads are movably mounted to caliper housing. The brake pads are pressed against a disc that is fixed to the wheel to halt the rotation of the disc and thus the wheel. The brake pads are moved toward the disc hydraulically or mechanically such as by a cam mechanism. The hydraulic disc brake systems are typically complicated in construction and expensive to manufacture. Moreover, hydraulic disc brake systems are often quite heavy in construction.
[0007] In both hydraulic and mechanical disc brake systems, the brake pads need to be spaced apart by a predetermined distance to receive the disc between the brake pads. The brake pads should be slightly spaced apart from the disc when the brake system is in the non-braking position. It is desirable to control the spacing between the brake pads and the disc to ensure good braking. Wear of the brake pads in turn reduces the braking ability of the vehicle. It also reduces the rider comfort as the free play of brake actuating member increases beyond a threshold limit and causes rider to apply more braking force to bring the vehicle to halt. Thus, when the brake pads and/or the disc become worn, the spacing between the brake pads and the disc becomes larger. Thus, the brake pads must be moved farther to engage and stop the disc.
[0008] Hence there is a requirement for an optimized braking system for a vehicle, which achieves the necessary trade-off between a disc braking system and a drum braking system, and which provides the above advantages associated with the disc brake. Disc brakes with recuperating seal for wear adjustment are known. Hence, there is also a requirement for a suitable brake pad wearing adjustment mechanism for such a braking system.
SUMMARY OF THE INVENTION
[0009] To obviate the above-stated problems of the existing disc and drum brake systems, the proposed invention describes a cylindrical cam based disc braking system. The proposed invention further describes a freewheel mechanism for applying and releasing brakes, and a cylindrical cam mechanism for actuating the brakes. The present invention, also describes a wear adjustment feature for the braking system. By usage of a wear adjustment feature, the initial position of the brake pads from the disc is kept within a predetermined tolerance range by using a ratchet and a pawl mechanism. The proposed invention on disc brake mechanism has better efficiency than a drum brake. By using the described disc brake herein, cost can be reduced, performance can be enhanced and periodical manual adjustments can be avoided.
[00010] In one embodiment of the present invention, a brake actuating member is connected to a brake lever using a cable. The brake lever is further connected to freewheel and capable of rotating freewheel in one direction. The described freewheel has a bearing mechanism with an inner and an outer race. The brake lever is rigidly joined to the outer race of freewheel and a cylindrical cam is mechanically coupled with an interference fit to the inner race of freewheel. The cylindrical cam is housed inside a caliper body with a portion of the cylindrical cam protruded outside the caliper body. The inner race of freewheel is mechanically coupled on to the protruded portion of the cylindrical cam. When the brake actuating member is operated, a cable rotates a brake lever. The brake lever, being rigidly joined to the outer race of freewheel transfers the rotation to the inner race of freewheel, to which the cylindrical cam is mechanically coupled with an interference fit. The cylindrical cam is rotated due to the rotation of the inner race of the freewheel. This is to be noted that, the outer race of freewheel is able to drive the inner race of freewheel in only one direction. The outer race of freewheel is capable to drive the inner race of freewheel, but the inner race cannot drive the outer race of freewheel. The cylindrical cam has a pair of converging grooves. One pushblock is provided in each groove. A pair of brake pads are located in-between the pushblocks and a disc is located in between the brake pads. The described elements which are the pushblocks, brake pads and the disc are held on a plurality of supporting studs and are capable of sliding on the studs with the studs themselves supported on two caliper bodies from both ends. When the cylindrical cam rotates, the pushblocks follow the converging grooves and push the brake pads closer to each other while sliding on the supporting studs. When the brake pads come closer enough to come in contact with the disc, the rotation of disc slows down and eventually brings the disc and the vehicle to halt. The groove on the cylindrical cam, which converges towards each other, determines the profile for movement of the pushblocks and eventually the linear movement of brake pads along the cylindrical cam.
[00011] In yet another embodiment of the current invention, a wear adjustment mechanism is described. The wear adjustment mechanism comprises of a wear adjuster ratchet, a wear adjuster pawl and an adjuster spring. There is enough clearance between the wear adjuster pawl and the cylindrical cam for relative motion between the two. The wear adjuster ratchet is rigidly fastened to the cylindrical cam using suitable fasteners. The wear adjuster ratchet and the wear adjuster pawl are further equipped with set of zig-zag teeth so that the teeth of wear adjuster ratchet is capable of engaging and sliding on the teeth of the wear adjuster pawl. The wear adjuster pawl has a set of teeth on one face at a first end portion, a pin on other face at the first end portion and a slot on a second end portion. The cylindrical cam passes through the above slot in the wear adjuster pawl. The adjuster spring is supported on the pin with one end butted against the wear adjuster pawl and other end on a first caliper -body on freewheel side. The wear adjuster ratchet and wear adjuster pawl are held under compression of the adjuster spring. The adjuster spring is kept under compression to apply force on the wear adjuster pawl so that the teeth portion on wear adjuster pawl is in continuous contact with the teeth portion on wear adjuster ratchet. The pin on the first caliper body is located inside a slot which is concentric to the axis of rotation of the cylindrical cam. This slot helps in retreating back of the pushblocks and brake pads after teeth are engaged for the first time.

BRIEF DESCRIPTION OF DIAGRAMS
[00012] Figure 1 illustrates a typical two-wheeler.
[00013] Figure 2 illustrates a typical wheel with a braking mechanism.
[00014] Figure 3 illustrates mechanical coupling of brake actuating member with brake lever.
[00015] Figure 4 illustrates free wheel and its inner race and outer race.
[00016] Figure 5 illustrates a perspective view of the braking system showing the wear adjustment.
[00017] Figure 6 illustrates a perspective view of the braking system showing the push blocks as per the present invention.
[00018] Figure 7 illustrates an exploded view of the braking mechanism according to the invention.
[00019] Figure 8 illustrates teeth engagement of wear adjuster ratchet and wear adjuster pawl in wear adjustment mechanism.
[00020] Figure 9 illustrates wear adjustment mechanism.
[00021] Figure 10 illustrates sliding mechanism of teeth of wear adjuster ratchet and wear adjuster pawl.
[00022] Figure 11 illustrates wear indicator for the braking system as per the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[00023] The working of the disc brake of a vehicle, according to present invention is described herein. A brake actuating member is connected to a brake lever using a cable. The actuation of the brake actuating member by a rider of the vehicle actuates the brake lever by means of transmission of actuating force through the cable. The brake lever has a first end coupled to the cable and a second end coupled to a freewheel. The actuation of the brake lever causes rotation of the freewheel. In an embodiment, the freewheel is capable of rotating in one direction. The freewheel described herein, comprises of an inner and an outer race. The inner race of the freewheel is mechanically coupled to a cylindrical cam. For instance, the cylindrical cam is rigidly attached to the inner race of the freewheel. The cylindrical cam is housed inside at least a first caliper body of a plurality of caliper bodies, with a portion of the cylindrical cam protruding outside the first caliper body. The inner race of the freewheel is mechanically coupled to the protruded portion of the cylindrical cam. When the brake actuating member is operated, a cable, which connects the brake actuating member and the brake lever, rotates the brake lever. In one embodiment, the brake lever is attached to the outer race of the freewheel and enable transferring the actuating forces to the inner race of the freewheel. In another embodiment, the brake lever is capable of being detachably attached to the outer race of the freewheel. The cylindrical cam is rotated due to the rotation of the inner race of the freewheel. The outer race of the freewheel is capable of unidirectionally driving the inner race of the freewheel. However, the inner race of the freewheel is not capable of driving the outer race of the freewheel. The cylindrical cam has a pair of converging grooves, each of which is provided with a push block. A pair of brake pads is disposed in between the push blocks, and a disc is located in between the brake pads. The push blocks and the brake pad are held on a plurality of supporting studs and are capable of sliding on the studs with the studs themselves supported on two caliper bodies from both ends. When the cylindrical cam rotates, the push blocks follow the converging grooves and push the brake pads closer to each other while sliding on the supporting studs. When the brake pads come in contact with the disc, the rotation of disc slows down and eventually brings the disc and the vehicle to halt. The groove on the cylindrical cam, which converges towards each other, determines the profile for movement of the push blocks and eventually the movement of brake pads along the cylindrical cam.
[00024] A torsional spring, at one end is fixed in a hole inside the first caliper body, which houses the freewheel. The other end of the torsional spring is mechanically coupled to the cylindrical cam. Thus, rotation of the cam causes the torsional spring to store torsional energy. When the brake actuating member is released, this torsional spring releases the torsional energy and ensures that the cam is rotated back to its original position. During this rotation of the cam, the inner race of the freewheel rotates. However, the outer race of the freewheel doesn’t rotate. The release of the brake actuating member also causes rotation of the brake lever to its original position with the help of the cable and a separate spring.
[00025] In yet another embodiment of the current invention, a wear adjustment mechanism is described. The wear adjustment mechanism comprises of a wear adjuster ratchet, a wear adjuster pawl and an adjuster spring. The wear adjuster ratchet is rigidly attached to the cylindrical cam. The wear adjuster ratchet and the wear adjuster pawl are further equipped with set of zig-zag teeth so that the teeth of wear adjuster ratchet are capable of engaging and sliding on the teeth of the wear adjuster pawl. The wear adjuster pawl has a set of teeth disposed on a first surface of a first end portion, and a pin disposed on a second surface of the first end portion, and a slot on a second end portion. The cylindrical cam passes through the slot in the wear adjuster pawl. The adjuster spring is disposed on the pin on the wear adjuster pawl and enables the spring to be held on the pin of the wear adjuster pawl in-between the first caliper body on the freewheel side and the wear adjuster pawl. The pin on the first caliper body is located inside a slot which is concentric to the axis of rotation of the cylindrical cam. This slot helps in retreating back of the pushblocks and brake pads after any teeth are engaged for the first time. The adjuster spring is kept under compression to transmit force to the wear adjuster pawl so that the teeth portion on wear adjuster pawl is in continuous contact with the teeth portion on the wear adjuster ratchet.
[00026] In brake system described herein, at the time of assembly of the braking system, the push blocks are separated apart by a maximum possible distance on the cam grooves. To ensure minimum clearance between brake pad and disc in the present invention, the mechanical advantage depends on the rotation of lever which is attached to the cam. Cam rotation along with the stud results in linear movement of push blocks which is equal to the amount of linear movement of brake pads. The required amount of linear movement of the brake pads to come in contact with the disc increases; once the brake pads wear off, hence to keep the mechanical advantage within required limits; in yet another embodiment of the current invention,, a wear adjuster ratchet and a wear adjuster pawl arrangement is used. As described earlier, the wear adjuster ratchet is attached to the cylindrical cam. When the cylindrical cam rotates, the push blocks moves towards each other causing the brake pads to move towards the disc disposed in-between. The typical wear off of the brake pads is continuous and gradual.
[00027] A brake system without a brake wear off adjustment will allow the full length of travel of push blocks in the cam grooves towards the converged end of the cam grooves and back to the diverged end of the cam groove. The present invention proposes wearing adjustment mechanism which in case of brake pad wear off, will inhibit the rotation of cam by a predetermined angle and hence the travel of push blocks back to the diverged end of the cam groove by a predetermined distance, which is determined by the amount of brake pad wear and is implemented by teeth engagement of wear adjuster ratchet and wear adjuster pawl.
[00028] The brake pads include plurality of brake liners, whose thickness from start to end of life of the brake pad is divided into a predetermined number of divisions. The wear adjuster ratchet and the wear adjuster pawl are provided with a predetermined number of teeth corresponding to the width of the brake liners, width which decides the life span of the brake liners. When the brake liners wear off beyond a first division of the brake pad life, the first teeth of the wear adjuster ratchet and the wear adjuster pawl get engaged. Thus, the rotation of the cam is inhibited by a predetermined angle due to the engagement of the wear adjuster ratchet teeth and the wear adjuster pawl teeth. A similar pattern is followed for the subsequent wear off of the brake pads and the retreating back of the cam is further inhibited to keep the mechanical advantage within a prescribed limit.
[00029] Furthermore, the described brake pads are located at a predetermined distance on both sides of the disc. The brake pads and the push blocks are slidably supported on a plurality of supporting studs. The push blocks and the brake pads are guided on at least two supporting studs and the supporting studs are supported on both the first and the second caliper bodies. In another embodiment, any other equivalent of studs can be implemented. The brake pads and the push blocks are made to freely slide on the supporting studs and the movement of the brake pads is governed by the movement of the push blocks. The push blocks in the middle portion have rollers rolling on cam grooves, which form a rotating pair of the push blocks. The push blocks are guided by plurality of studs and equipped with rollers which aid the push block to move inside the groove on the cam as cam rotates.
[00030] The cylindrical cam is equipped with sliding slots for the rollers which in turn guides the sliding of the push blocks on the cam. The wear adjuster ratchet is attached to the cam by using suitable fasteners, for example, a ratchet screw. This wear adjuster ratchet as described herein, has a predetermined number of zig zag steps also called as teeth and also has a small seating hole for inserting the fastener..
[00031] A mounting clamp couples the disc brake to vehicle’s wheel by using spacers
[00032] The above described braking system has reduced braking distance compared to a disc brake and an optimized wear adjustment arrangement to maintain a constant braking feel throughout the life of the brake pads. The different embodiments of the current invention would be understood in more detail further when described in a more detail with the description of the drawings.
[00033] Figure 1 shows a typical two-wheeled vehicle (10) with a fuel tank (1), rider seat (2), rear wheel (3), center stand (4), engine (5), front wheel (6), and front suspension (7), head lamp (8), front brake (9) and a brake actuating member (11). The hand lever (11) is brake actuating member which is further connected to a brake lever (25) through a cable (91). Furthermore, a brake pedal and a hand lever are synonymous to a brake actuating member for the purpose of understanding the described invention herein. The braking system as shown in Figure 1 and described herein is not limited to only front wheel, but could also be disposed on the rear wheel (3).
[00034] Figure 2 shows front wheel (6), front suspension (7), freewheel (21), brake disc (22), and holder plate (23), an adjuster spring (24) and braking system (20). The freewheel (21) is a part of the braking system which brings back a brake lever (25) (shown in Figure 4) to its original position after the brake actuating member (11), has been released. The brake lever (25), when rotated in one direction, rotates a cam (28) (shown in Figure 5). The brake lever (25) retreats back to its original position when the brake actuating member (11) is released.
[00035] Figure 3 shows the mechanical coupling of brake actuating member, cable and brake lever. The hand lever (11) is the brake actuating member which is further connected to a brake lever (25) through a cable (91). The brake actuating member (11) is operated to actuate brake and upon release of the brake actuating member (11), the brake lever (25) retracts back to its original position due to the combined effect of the cable (91) shown in Figure 4 and the separate spring (93) shown in Figure 3.
[00036] Figure 4 illustrates the free wheel construction with inner race (101) and outer race (102). The inner race (101) and the outer race (102) are mechanically coupled through a one way bearing mechanism. This one way bearing mechanism allows the transmission of force from the outer race (102) to the inner race (101) only and inhibits any transmission of force from inner race to outer race.
[00037] Figure 5 shows the perspective view of the internal construction of the braking system as per the present invention. Figure 5 shows first stud S1, braking system (20), freewheel (21), brake lever (25), torsional spring (41), cam (28), cam grooves (29), wear adjuster pawl (30), a wear adjuster ratchet (32), first push block (34), middle portion of first push block (35), first brake pad (36), middle portion of second push block (38), a second brake pad (39) and a gap “G” between the brake pads.
[00038] The stud S1 supports the first push block (34), second push block (37), first brake pad (36), second brake pad (39) through atleast one pass through slot in the first push block (34), second push block (37), first brake pad (36) and second brake pad (39). A second stud S2 shown in Figure 6 supports the first push block (34), second push block (37), first brake pad (36), second brake pad (39) through atleast one pass through slot in the first push block (34), second push block (37), first brake pad (36). Both the ends of the studs S1 and S2 are further supported on two caliper bodies.
[00039] The torsional spring (41) is supported in a hole in the caliper body at one end and to a hole in the wear adjuster ratchet (32) at the other end. The wear adjuster ratchet (32) is attached to the cylindrical cam (28). An actuation of brake lever (25) through activation of the brake actuating member (11) rotates the cam (28) and brings the torsional spring (41) under torsion. Hence, upon operating brake actuating member (11), the brake lever (25) rotates the outer race (102) which drives the inner race and simultaneously rotates a cam (28) shown in Figure 6. When brake actuating member (11) is released, the brake lever (25) rotates freely, retracts to original position by help of an additional spring (93) shown in Figure 3. Furthermore, the operation of brake actuating member (11) results in rotation of brake lever (25) which rotates the cam (28) and simultaneously loads the torsional spring (41), and due to concurrent rotation of the cam, the pushblocks (34) and (37) slide inside a converging groove to follow a converging path. The pushblocks move the brake pads (36), (39) towards the disc (22) which eventually results in application of brakes when the brake pad (36), (39) touches the disc (22). Upon release of the brake actuating member (11), the torsional spring (41) shown in Figure 5 retracts back the cam (28) due to released torsional energy which eventually results in retracting back the brake pads (36), (39) away from said disc (22) and the disc (22) is relieved from the brake application. In addition, upon release of the brake actuating member (11), the brake lever (25) retracts back to its original position due to the combined effect of the cable (91) shown in Figure 3 and the separate spring (93).
[00040] Figure 6 shows another perspective view of the internal construction of the braking system (20) as per the present invention. Figure 6 shows first Stud S1, second stud S2, braking system (20), brake lever design (25), cam (28), second push block (37), middle portion second push block (38) and a second brake pad (39). As illustrated, the push blocks (34) and (37) accommodates the brake pad (36) and brake pad (39) with the middle portion second push block (38) and middle portion first push block (35) inside the respective cam grooves (29). On actuation of the brake lever (25), the attached cam (28) rotates, due to which the middle portion second push block (38) and middle portion first push block (35) starts following the path as per the profile of cam grooves (29). The cam groove (29) is equipped with a converging profile which guides the middle portion second push block (38) and middle portion first push block (35) and brings them towards each other due to the restricted converging profile. The brake pads (36) and brake pads (39), which are disposed between the middle portions second push block (38) and middle portion first push block (35) are free to slide on the studs S1 and S2, are also brought closer. This movement of the brake pads (36) and brake pads (39) towards each other results in the application of brakes when the brake pads (36) and brake pads (39) touch the disc (22).
[00041] Figure 7 shows exploded view of the braking system (20). Figure 7 shows brake lever (25), freewheel (21), a first caliper body (27), second caliper body (42), cam (28), cam grooves (29), wear adjuster pawl (30), teeth (31) of wear adjuster pawl, wear adjuster ratchet (32), teeth (33) of wear adjuster ratchet, first push block (34), middle portion first push block (35), pushblocks, second push block (37), middle portion second push block (38), pushblocks, clamp holder (40) and torsional spring (41). The first caliper body (27), torsional spring (41), wear adjuster pawl (30), wear adjuster ratchet (32), first brake pad (36), second brake pad (39), first push block (34) and second lever (37) are held between said first caliper body (27) and second caliper body (42) by help of thorough stud S1 and stud S2. In the present context, by two thorough studs S1 and stud S2, it is meant that the studs S1 and S2 are supported in a slot in the first caliper body (27) at one end and passes through first push block (34), first brake pad (36), second brake pad (39) and second push block (37) and again supported in a slot in the caliper body (42) at other end. The first pushblock (34) and second pushblock (37) are held in the cylindrical cam by set of screws (34R, 37R), and the cylindrical cam passes through the first caliper body (27) through an opening (43). The inner surfaces of first brake pad (36) and second brake pad (39), facing the disc come towards disc (22) to apply the brakes. For proper functioning of the brakes, the gap ‘G’ between the brake pads must be maintained within a predetermined range throughout the life of the brake pad so that the brake actuating member (11) has to be operated with same force and for same span to apply the brakes. When we discuss the gap between the brake pads, it implies the gap between the inner surfaces of the brake pads that is the brake liner which comes in contact with the disc to apply the brake.
[00042] The brake lever (25) is attached to the outer periphery of the freewheel (21). Freewheel (21) has a bearing mechanism such that the inner race (101) (shown in Figure 4) of the freewheel (21) accommodates said cam (28). The outer race (102) (shown in Figure 10) of the freewheel (21) is rigidly joined to the brake lever (25). The brake lever (25) is made capable to rotate relative to the freewheel (21) in only one direction. On operating the brake actuating member (11) which is further connected to the brake lever (25) through an inextensible cable (91), the torsional spring (41) that covers the outer periphery of the cam (28) undergoes torsional stress. After releasing the brake actuating member (11), the brake lever (25) comes to its original position due to release of torsional stress from the torsional spring (41).
[00043] Figure 8 shows the detailed construction of wearing adjustment mechanism. Figure 8 further illustrates the first caliper body (27), cam (28), and cam grooves (29); wear adjuster pawl (30), wear adjuster ratchet (32) and torsional spring (41). Due to wearing off of the brake pads, the gap “G” shown in Figure 5 between the two brake pads will keep on increasing. Due to this increased brake pad gap “G”, the lever stroke (for the brake actuating member (11)) will increase & mechanical advantage will decrease and hence brake application becomes incomprehensible.
[00044] The wear adjustment mechanism comprises of a wear adjuster ratchet (32), a wear adjuster pawl (30) and an adjuster spring (74). Enough clearance is provided between the wear adjuster pawl (30) and the cylindrical cam (28) for relative motion between the two. The wear adjuster ratchet (32) is attached to the cylindrical cam (28) using suitable fasteners (72). The wear adjuster ratchet (32) and the wear adjuster pawl (30) are further equipped with set of zig-zag teeth (33), (31) so that the teeth (33) of wear adjuster ratchet is capable of engaging and sliding on the teeth (31) of the wear adjuster pawl. The wear adjuster pawl (30) on one end portion has a set of teeth (31) on one face and a pin (73) on other face and a slot on the other end portion. The cylindrical cam (28) passes through the slot in the wear adjuster pawl (30). An adjuster spring (74) is supported on the pin (73) on the wear adjuster pawl (30) and held in-between the first caliper body (27) on freewheel side and the wear adjuster pawl (30). The adjuster spring (74) is held under compression to apply force on wear adjuster pawl (30) to butt against the wear adjuster ratchet (32). Furthermore, the adjuster spring (74) transmits force to the wear adjuster pawl (30) so that the teeth portion (31) on wear adjuster pawl (30) is in continuous contact with the teeth portion (33) on wear adjuster ratchet (32).
[00045] A brake system without a brake wear off adjustment will allow the full length of travel of push blocks (34), (37) in the cam grooves (29) towards the converged end of the cam grooves and back to the diverged end of the cam groove. In general, mechanical advantage of a system is a measure of the force amplification achieved by using a tool, mechanical device or machine system. The mechanical device in the present invention is the braking system. The mechanical advantage of the current invention is determined by combination of the required amount of movement of pushblocks (34),(37) in the cam grooves (29) and the required amount of linear movement of brake pads (36),(39) on the supporting studs S1,S2, to touch the disc (22). In case of wear off, the gap “G” between the brake pads (36), (39) increases, which results in a longer travel of brake pads required for coming in contact with the disc (22). Hence, an increase in the amount of linear movement of brake pads (36),(39) required to bring the brake pads (36),(39) in contact with the disc (22) can be adjusted by reducing the required amount of movement of the pushblocks (34), (37). This forms the fundamental basis of the described wear adjustment mechanism.
[00046] Hence, in brake system described herein when there is no wear on the brake pads (36), (39) initially, the pushblocks (34), (37) are separated apart by a maximum possible distance on the cam grooves (29). The required amount of linear movement of brake pads (36), (39) to touch the disc (22) increases once the brake pads (36), (39) wear off, hence to keep the mechanical advantage within required limits; it is an objective of the current invention to provide a means to reduce the retreating distance travelled by the pushblocks (34), (37) so that during operation of brake actuating member, the pushblock(34), (37) have to travel a lesser distance. The distance travelled by the pushblock (34), (37) is inhibited by inhibiting the rotation of cam (28) while the cam retreats back to its original position during release of the brake actuating member (11). The present invention will inhibit the rotation of cam (28) by a predetermined angle and hence the travel back of pushblocks (34), (37) towards the diverged end (53) of the cam grooves (29) by a predetermined distance. This predetermined distance by which the travel back of pushblock (34), (37) to the diverged end (53) is inhibited, is determined by the amount of brake pad wear and is implemented by teeth (33) engagement of wear adjuster ratchet (32) and wear adjuster pawl (30).
[00047] To calculate number of teeth (31), (33) in the wear adjuster ratchet (32) and wear adjuster pawl (30), the thickness of the brake liner of the brake pads (36), (39) from start to end of life of the brake pad is divided into a predetermined number of divisions. The wear adjuster ratchet (32) and the wear adjuster pawl (30) are provided with predetermined number of teeth (33), (31) corresponding to brake liner width which decides life span of the brake liner. When the wear off of the brake liner crosses the first division of the brake pad life, the first teeth (33) of the wear adjuster ratchet (32) and the wear adjuster pawl (30) get engaged. Thus rotation of the cam (29) is inhibited by a predetermined angle due to engagement of the teeth (33) of wear adjuster ratchet and teeth (31) of wear adjuster pawl. In a similar fashion, with continuous wear off of the brake pad (36), (39), more number of teeth (31), (33) gets engaged and the retreating back rotation of the cam (28) is further inhibited to keep the mechanical advantage in prescribed limit.
[00048] Furthermore, the described brake pads (36), (39) are located at a predetermined distance on both sides of the disc (22). The brake pads (36), (39) and the pushblocks (34), (37) are slidably supported on a plurality of supporting studs S1, S2. The pushblocks (34), (37) and the brake pads (36),(39) are supported and guided on atleast two supporting studs S1, S2 and the supporting studs S1, S2 are supported on two caliper bodies (27), (42). The described guiding means can take any other equivalent form apart from studs S1, S2. The brake pads (36), (39) and the pushblocks (34), (37) are made capable to freely slide on the supporting studs S1, S2 and the movement of the brake pads (36), (39) is governed by the movement of the pushblocks (34), (37). The pushblocks (34), (37) in the middle portion have rollers (35), (38) rolling on cam grooves (29) which form a rotating pair of the pushblocks (34), (37). The pushblocks (34), (37) are equipped with rollers (35), (38) which aid the pushblock (34), (37) to rotate on the groove (29) on cam (29) thereby forming a sliding pair within the grooves (29) of the cam (28).
[00049] The cam (28) is equipped with grooves (29) for the rollers; the walls of the groove (29) further guide the sliding and rolling of the pushblocks (34), (37) on the cam (28). The wear adjuster ratchet (32) is rigidly attached to cam (28) by using suitable fasteners (72) here named as ratchet screw. This wear adjuster ratchet (32) as described herein has predetermined number of zig zag steps also called as teeth and also has a small seating hole for the inserting the fastener (72). Further described is a wear adjustor pawl (30) which surrounds the periphery of cam and is also capable of freely rotating on outer periphery of cam (28). The pin (73) on wear adjuster pawl (30) sits in an oval slot in first caliper body (27) and is surrounded by the adjuster spring (74). The pin (73) is housed in a slot in first caliper body (27). The pin (73) is preferably concentric with the cylindrical cam axis of rotation and is further provided with a pre-determined amount of play, so that the pin (73) is held loosely inside the slot of caliper body (27). Pin (73) plays a vital role in releasing the brake pads from contact with disc (22) every time a new tooth of the wear adjuster ratchet and the wear adjuster pawl is engaged by rotating back the cam. The adjuster spring (74) is held under compression in assembled condition and is held between the wear adjuster pawl (30) and the first caliper body (27) accommodating the freewheel. The adjuster spring (74) functions to keep the teeth portions (33), (31) of the wear adjuster ratchet (32) and the wear adjuster pawl (30) in contact.
[00050] The present invention describes a brake wearing adjustment in which the increase in gap “G” between brake pads due to wearing off is maintained within a pre-determined range. For the wearing adjustment, illustrated in Figure 8, the teeth (31) of wear adjuster pawl and teeth (33) of wear adjuster ratchet try to have relative motion with respect to each other. The teeth are aligned in such a way that, if the teeth (31) of wear adjuster pawl crosses any corresponding teeth (33) on wear adjuster ratchet, it can’t retreat back. This distance between the two teeth (31), (33) of wear adjuster pawl or wear adjuster ratchet is related to the brake pad wearing. For every predetermined amount of brake wearing, i.e. increase in gap “G”, the teeth alignments shift at least by one tooth. Since the wear adjuster ratchet (32) is attached to the cam, this teeth engagement between the wear adjuster ratchet (32) and wear adjuster pawl (30) inhibits the retreating back rotation of the cam and thus maintaining the pushblock and brake pads to a new location in the cam groove (29). This helps in keeping the mechanical advantage of the brake system in a constant range even after wearing off of the brake pad till a certain limit.
[00051] Figure 9 shows the first caliper body (27), cam (28), cam grooves (29), teeth (31) of wear adjuster pawl and teeth (33) of wear adjuster ratchet. In the present illustration, the brake pads. The pin (73) is located inside a slot (75) inside the first caliper body (27). The profile is further concentric to the axis of rotation of the cylindrical cam. The slot (75) aids in bringing back the pushblock and brake pads away from disc during teeth engagements of wear adjuster ratchet and wear adjuster pawl.
[00052] Figure 10 shows another perspective view of the wearing mechanism with the cam (28), cam grooves (29), teeth (31) of wear adjuster pawl and teeth (33) of wear adjuster ratchet. To achieve the wearing off adjustment, the wear adjuster pawl (31) and wear adjuster ratchet (32) are clamped through an adjuster spring (74) which continuously pushes the two coinciding teeth (31), (33) of wear adjuster pawl and wear adjuster ratchet over one another. Due to zig-zag profile of the two coinciding teeth portions of the wear adjuster pawl (30) and wear adjuster ratchet (32), they cannot retreat back. Once one tooth has been passed, no retreating back on those teeth helps in maintaining gap between the two brake pads (36) and (39) within a pre-determined range. The wear adjuster pawl (30) and wear adjuster ratchet (32) rotate and slide over each other. The wear adjuster pawl (30) will rotate before the tooth (33) of wear adjuster ratchet slides over it. Wear adjuster pawl (30) rotates till the brake pads are displaced by a predetermined distance which is ensured by the slot in the first caliper body (27). Wear adjuster pawl (30) will get locked by one tooth in wear adjuster ratchet (32) when the brake pads wear reaches for a pre-determined distance.
[00053] In yet another embodiment of the current invention, a wear indicator for the braking system is described. Figure 11 shows the brake lever (25), cylindrical cam (28), a wear indicator needle (102) and an indicator screw (101). The wear indicator needle (102) is fastened at one end face of the cylindrical cam (28) by indicator screw (101). The wear indicator needle (102) shifts by one gradation over the wear gradation scale (103) every time a new set of teeth of the wear adjuster pawl and the wear adjuster ratchet is engaged. The wear indicator needle (102) points to a wear gradation scale (103) corresponding to a successive stage of wear of the braking system. The wear gradation scale (103) is marked on the first caliper body (27).
[00054] The present subject matter is thus described. The description is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above description. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore the foregoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the appended claims.
,CLAIMS:We claim:
1. A braking system (20) for an automobile (10), the braking system (20) comprising:
a brake actuating member (11) to enable operation of said braking system (20);
a disc (22) comprising a first side (22A) and a second side (22B), wherein said disc (22) being fixedly attached to a wheel (6) and rotatable about a central axis of said wheel (6);
a brake lever (25) operably connected to said brake actuating member (11), wherein said brake lever (25) is actuated by said brake actuating member (11) through a cable (91);
a cylindrical cam (28) comprising a first end (28 F) and a second end (28 S), wherein said first end (28 F) supported on a first caliper body (27) through an opening (43), and said second end (28 S) supported on a second caliper body (42);
a pair of converging grooves (29) embedded on a lateral surface of said cylindrical cam (28);
a pair of push block (34, 37) disposed in said cylindrical grooves (29) through a pair of screws (34R, 37R);
a pair of brake pads (36, 39) disposed on said pair of push block (34, 37) being juxtaposed on said two sides (22A, 22B) of said disc (22), and wherein said pair of brake pads (36, 39) comprising a gap G in between;
a pair of studs (S1, S2) fixable mounted between said fist caliper body (27) and said second caliper body (42); and
said cylindrical cam (28) rotates moving at least one pushing block (34, 37) along said pair of studs (S1, S2) towards each other, wherein movement of at least one of said push block (34, 37) causes corresponding movement of said brake pads (36, 39) towards each other, and wherein said movement of the brake pads (36, 39) transfers braking forces to said disc (22).
2. The braking system (20) as claimed in claim 1, wherein said brake lever (25) is attached to a freewheel (21) through a cable (91), wherein said freewheel (21) comprising of an inner race (101) and an outer race (102), such that said outer race (102) is attached to said brake lever (25) and said inner race (101) being formed within said outer race (102) to enable said outer race (102) to drive said inner race (101) on being rotated by said brake lever (25) upon pressing of said brake actuating member (11), and wherein said inner race (101) is capable of rotating said outer race (102) in only one direction, and said outer race (102) is capable of rotating said inner race (101) in only one direction.
3. The braking system (20) as claimed in claim 1, wherein said cylindrical cam includes a torsional spring (41) enveloped around it placed in a slot disposed on said first caliper body (27) such that said torsional spring (41) is stored the energy on application of said brake actuation member (11) with rotation of said cylindrical cam (28), and upon release of said brake actuating member (11) said torsional spring (41) retracts back to bring back said cylindrical cam (28) to original position through discharge of torsional energy stored in said torsional spring (41) thereby releasing application of said braking system
4. The braking system (20) as claimed in claim 1, wherein said cylindrical cam (28) passes through a wear adjuster pawl (28) being disposed in a slot (75) on said first caliper body (27) through a pin (73) and includes a set of teeth (31), and wherein said cylindrical cam (28) includes a wear adjuster ratchet (32) having a set of teeth (33) mounted on it through fasteners (72), such that said wear adjuster pawl (30) is in a continuous contact with said wear adjuster ratchet (32) through said set of teeth (33, 31), and allowing said wear adjuster ratchet (32) to rotate around said wear adjustment pawl (30) by engagement of said set of teeth (33, 31) resulting in a constant gap G to be maintained between said pair of brake pads (36 & 39) even in a case of wearing of said brake pads (36 & 39), and wherein said pin (73) on the first caliper body (27) is located inside said slot (75) concentric to the axis of rotation of the cylindrical cam (28), and said slot (75) enabling retreating back of the pair of push blocks (34,37) and brake pads (36, 39) after teeth (33) are engaged for the first time.
5. The braking system (20) as claimed in claim 4, wherein said pin (73) includes a spring (74) being mounted on it, and wherein said spring (74) is held under compression in between said wear adjuster pawl (30) and said first caliper body (27) to apply force on said wear adjuster pawl (30) to remain in contact with said wear adjuster ratchet (32) along said set of teeth (31, 33).
6. The braking system (20) as claimed in claim 4, wherein said wear adjuster ratchet (32) being mounted on said cylindrical cam (28), rotation of said cylindrical cam (28) causes the push blocks (34, 37) to move towards each other causing the brake pads (36, 39) to move towards the disc (22) disposed in-between.
7. The braking system (20) as claimed in claim 6, wherein the wearing off of the brake liners beyond a pre-determined thickness causes engagement of the first teeth (31) of the wear adjuster ratchet (32) and the wear adjuster pawl (30), and wherein the rotation of the cam (28) is inhibited by a predetermined angle due to the engagement of the wear adjuster ratchet teeth (31) and the wear adjuster pawl teeth (33).
8. The braking system (20) as claimed in claim 4, wherein said wear adjuster ratchet (32) rotates around said wear adjuster pawl (30) by engagement of said set of teeth (33, 31), such that said cylindrical cam (28) is rotated causing pushing of said push blocks (34, 37) in said pair of converging grooves (29) to maintain pre-determined value of said G without changing said pre-determined angle of said brake lever (25).
9. The braking system (20) as claimed in claim 4, wherein during engagement of a new teeth among said set of teeth (33 & 31) of said wear adjuster ratchet (30) and said wear adjuster pawl (32) an indicator screw (45) rotates resulting in rotation of a wear indicator needle (50) fastened through said indicator screw (45) at one end face of said cylindrical cam (28), wherein said indicator needle (50) moves by one gradation over a wear gradation scale (55) printed on said first caliper body (27) to show level of wearing of said pair of brake pads (36 & 39).