TECHNICAL FIELD
[0001] The present subject matter relates to a vehicle. More particularly, the
present subject matter relates to a hydraulic braking system for a three-wheeled vehicle.
BACKGROUND
[0002] In many of the developing & under developed countries, a motor
vehicle particularly a three-wheeled automotive vehicle is a significant mode of public transportation. It is vastly used as a point to point mode of transport in rural and urban areas. While negotiating heavy traffic, it is imperative that these vehicles stop quickly within a short distance, even when the response time available for a driver is minuscule. Thus, there has been a growing need for the safer and more reliable braking systems. To meet this need, most of the vehicles now in use are utilizing a hydraulic braking system. The hydraulic braking system in communication with a hydraulic brake sub-assembly provides the most important safety system being able to slow down or stop the vehicle when required.
[0003] Typically, the hydraulic brake sub-assembly for the hydraulic braking
system of the vehicle comprises of a cylindrical structure having a bore therethrough and supporting two pistons, an anchor plate for receiving an anchor reaction force acting on said two pistons, seal cups for each of the piston and a sealing member for preventing foreign matter from entering the cylindrical structure and closes the gap between the two piston and the cylindrical structure of the hydraulic brake sub-assembly.
[0004] In a known hydraulic braking system, the sealing member is usually
designed in a way that it is mounted on the outer periphery of the cylindrical structure such that it is outward in onto both ends of the cylindrical structure of the hydraulic brake sub-assembly. The sealing member is designed to endure cyclic load, but not resist sudden impact load. Therefore, during assembling or servicing, any impact force tends to puncture a hole into the sealing member and

necessitates its immediate replacement. Further, the conventional sealing member of the hydraulic brake sub-assembly is designed to protect the cylindrical structure of the hydraulic brake sub-assembly from entry of dust, mud and water entry. However, during the continuous cyclic load, the sealing member expands and contracts under the continuous back and forth axial displacement of the piston. Thus, normal wear of said sealing member causes corrosion and pitting of at least a portion until the seal cups of the cylindrical structure of said hydraulic brake sub-assembly. However, over time, the bore of the cylindrical structure may become rough and cause the seal cups for each of the piston to wear out and hence get damaged. Such damage can result in leakage of brake fluid from the cylindrical structure or the pistons. Thus, the leaking of brake fluid results in corrosion and pitting to occur inside the cylindrical structure beyond said seal cups as moisture builds up in the brake fluid and the corrosion inhibitors in the fluid break down. The leaky hydraulic brake sub-assembly is dangerous because it may allow a complete loss of hydraulic pressure in the affected brake circuit. This, in turn, can cause the braking system of the vehicle to fail.
[0005] In another known conventional hydraulic braking system, the
cylindrical structure of the hydraulic brake sub-assembly is made up of cast iron. The cast iron cylindrical structure of the hydraulic brake sub-assembly is prone to rust as it gets corroded when the brake fluid gets contaminated with water or moisture. Hence, in order to increase the life of the hydraulic brake sub-assembly, the cast iron cylindrical structure is converted into aluminum cylindrical structure. However, the overall cost of hydraulic brake sub-assembly with aluminium made cylindrical structure increases 2 to 3 times. Thus, using aluminium made cylindrical structure instead of the cast iron is not cost effective and hence not feasible. Thus, in the existing hydraulic brake sub-assembly for the hydraulic braking system of the three-wheeled vehicle, the conventional positioning of the sealing member to the outer periphery of the cylindrical structure and the cast iron cylindrical structure of the hydraulic brake sub-assembly reduces the overall efficiency of the braking system and hence involves high replacement costs of the hydraulic brake sub-assembly.

[0006] Hence, there persists a need for manufacturing an improved hydraulic
brake sub-assembly which is cost effective. Further, it is desirable to provide an improved hydraulic brake system with a modified hydraulic brake sub-assembly structure with an improved designing and positioning of the sealing member to each end of the cylindrical structure of the hydraulic brake sub-assembly in the manner such that it doesnot worn or tear out easily and hence increases the shelf and operational life of the hydraulic brake sub-assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The detailed description is described with reference to the
accompanying figures. The same numbers are used throughout the drawings to reference like features and components.
[0008] Fig. 1. shows a side view of a three-wheeled vehicle according to one
embodiment of the present invention.
[0009] Fig. 2. illustrates an enlarged plane view of a pair of rear wheel of the
three-wheeled vehicle with a hydraulic brake sub-assembly disposed therein, according to one embodiment of the present invention.
[00010] Fig. 3. illustrates the hydraulic brake sub-assembly being mounted on
a backing plate between the brake shoes of a brake drum as per one embodiment of the present invention.
[00011] Fig. 4. & Fig. 5 illustrates a hydraulic brake sub-assembly being
disposed between the brake shoes of the brake drum as per one embodiment of the present invention.
[00012] Fig. 6. shows illustrates a perspective view of the hydraulic brake
sub-assembly as per one embodiment of the present invention.
[00013] Fig. 7. shows a perspective exploded view illustrating one end of the
hydraulic brake sub-assembly as per one embodiment of the present invention.
[00014] Fig. 8. illustrates an exploded sectional view of the hydraulic brake
sub-assembly in Fig.7.

[00015] Fig. 9. shows a perspective exploded view illustrating both end of the
hydraulic brake sub-assembly.
[00016] Fig.10 shows a front view of the hydraulic brake sub-assembly of
Fig.6, as per one embodiment of the present invention.
[00017] Fig.11. shows a sectional view of the hydraulic brake sub-assembly
of Fig 10, as per one embodiment of the present invention.
[00018] Fig.12 shows a side view of the hydraulic brake sub-assembly of
Fig.6 along a longitudinal plane as per one embodiment of the present invention.
[00019] Fig.13. illustrates a sectional view of the hydraulic brake
sub-assembly of Fig.12 along a transverse plane as per one embodiment of the present invention.
DETAILED DESCRIPTION
[00020] Most vehicles are equipped with a brake system for slowing or
stopping movement of the vehicle in a controlled manner. The brake system can be actuated by hydraulic, pneumatic, or mechanical pressure generated by an operator of the vehicle depressing a foot pedal, pulling a hand lever, and the like.
[00021] A typical hydraulic braking system for the three-wheeled vehicle
includes a brake drum for a front wheel as well as a pair of rear wheels of the vehicle. The brake drum consists of two cooperatively engaging brake shoes. The ends of these two brake shoes operatively engage each other through an adjusting strut between two of the cooperating ends. Between the other two cooperating ends of the brake shoes, a hydraulic brake sub-assembly is positioned.
[00022] Generally, the hydraulic brake sub-assembly consists of a cylindrical
structure having a bore therethrough and two pistons, one on each side. Each piston has a sealing member made up of a rubber and a shaft that connects the piston with the brake shoe. The hydraulic brake sub-assembly works on the principle that when a driver of the vehicle steps on a brake pedal, hydraulic pressure from the master cylinder pushes the two pistons inside the cylindrical structure outwardly to force the brake shoes against the drums and apply the

brakes. When the brake pedal is released, return springs pull the shoes back away from the drums and push the pistons back into the bore.
[00023] In a conventional hydraulic braking system, the cylindrical structure
of the hydraulic brake sub-assembly is made up of cast iron or aluminium alloy, and they operate under extreme pressures and temperatures. All cast iron type cylindrical structure are prone to rust and corrosion during the application of brakes. Thus, the cylindrical structure of the hydraulic brake sub-assembly gets corroded when brake fluid gets contaminated with water or moisture. Thus, affecting shelf life as well as operational life of the hydraulic brake sub-assembly. The brake fluid is generally glycol based fluids and is highly hygroscopic in nature. So, the cast iron body of the cylindrical structure gets corroded when the brake fluid gets contaminated with water or moisture.
[00024] In a known hydraulic braking system, the cast iron made cylindrical
structure of the hydraulic brake sub-assembly has been replaced by aluminium in order to increase the life hydraulic brake sub-assembly. However, using aluminium made cylindrical structure instead of the cast iron results in an increased cost of manufacturing for hydraulic brake sub-assembly.
[00025] In another known conventional hydraulic braking system for the
three-wheeled vehicle, a rotating brake drum is attached to a front wheel, a pair of rear wheels and two expanding brake shoes. When brake pressure is applied, the brake fluid flows through a hydraulic line towards the cylindrical structure of the hydraulic brake sub-assembly located between the brake shoes. The sealing member present on each end of the cylindrical structure of the hydraulic brake sub-assembly prevents dirt and dust from entering and fouling the hydraulic brake sub-assembly and in addition provides protection against immediate leakage of the brake fluid out from the hydraulic brake sub-assembly. Generally, the hydraulic brake sub-assembly is subject to continuous cyclic load and the sealing member is usually designed in such a way that they are fitted to the outer periphery of the cylindrical structure. Therefore, during assembling or servicing,

any impact force tends to puncture and cause a hole into the sealing member and thus necessitates its immediate replacement.
[00026] With the above objectives in view, the present invention discloses the
improved hydraulic brake sub-assembly for the hydraulic braking system with the modified cylindrical structure having inner lining aluminum and outer periphery with cast iron or plastic, hence preventing the contamination of the brake fluid and the corrosion of the cylindrical structure of the hydraulic brake sub-assembly. The object of the present invention relates to the hydraulic brake sub-assembly disposed on the brake drum associated with the front wheel and said pair of rear wheels of the three-wheeled vehicle. The brake drum includes said two engaging brake shoes and the hydraulic brake sub-assembly being disposed between the opposed ends of the brake shoes.
[00027] According to one embodiment of the present invention, the
three-wheeled vehicle comprises of the front wheel and said pair of rear wheels. The hydraulic braking system of the vehicle comprises of a front brake unit being associated with said front wheel and a rear brake unit associated with said pair of rear wheels. In one embodiment a brake drum is fixably attached to an inner surface of said front wheel and said pair of rear wheels, respectively. The hydraulic brake sub-assembly is disposed in the brake drum comprising of the cylindrical structure having the bore formed therethrough. As per one embodiment of the present invention said cylindrical structure of the hydraulic brake sub-assembly comprises of a first hollow cylinder and a second hollow cylinder. The first hollow cylinder and said second hollow cylinder are firmly attached together through press-fitting such that the alignment of said first hollow cylinder with said second hollow cylinder prevents the rotation of said both cylinder in either direction. As per one embodiment of the present invention, said hydraulic brake sub-assembly comprises of the sealing member provided at both the ends of said cylindrical structure and secured inwardly to an inner periphery of said cylindrical structure through an engaging member. According to one embodiment of the present invention, said engaging member is a circular retainer

plate made up of metal. In another embodiment, said circular retainer plate is made up of a resin material such as plastic. The engaging member comprises of a plurality of retaining slots being adapted into a plurality of grooves provided on said inner periphery of said cylindrical structure. In one embodiment of the present invention, said sealing member is secured to said both ends of the cylindrical structure of said hydraulic brake sub-assembly in an inward out manner thereby preventing damage, such as corrosion damage to the cylindrical structure inner surface and further preventing said the seal cups from getting worn out and damaged. Thus, preventing immediate and high replacement cost for the hydraulic brake sub-assembly for the vehicle braking system. Referring to one embodiment of the present invention, the first hollow cylinder is made up of a cast iron and said second hollow cylinder of an aluminium alloy. In another embodiment, the first hollow cylinder is made up of a resin material such as plastic and said second hollow cylinder of said aluminium alloy. The second hollow cylinder is having a diameter smaller than that of the first hollow cylinder and hence, as per one embodiment, said second hollow cylinder is press-fitted into the first hollow cylinder.
[00028] Referring to one embodiment, the hydraulic brake sub-assembly
comprises cylindrical structure having said bore, two oppositely acting pistons sliding inside the bore. According to one embodiment of the present invention, the cylindrical structure includes the first hollow cylinder and the second hollow cylinder with the second hollow cylinder being press fitted into the first hollow cylinder in the manner that the bore that is the inner periphery of the cylinder structure is made up of the made up of said aluminum alloy and whereas the outer periphery of the cylindrical structure is made up of cast iron or plastic. As per another embodiment, the first hollow cylinder is made up of a resin material such as plastic and said second hollow cylinder of said aluminium alloy. Thus, increasing the durability of the hydraulic brake sub-assembly. The inner periphery of the cylindrical structure that is the bore with aluminum lining improves corrosion resistance. As per one embodiment of the present invention, the inclusion of the aluminum alloy lining to the cylindrical structure by press-fitting

the second hollow cylinder into the first hollow cylinder prevents the corrosion, rusting to the hydraulic brake sub-assembly structure also preventing the leakage of the brake fluid and hence increasing the shelf life of the hydraulic brake sub-assembly According to one embodiment of the present invention, the sealing member provided at both ends of said cylindrical structure is made up of resilient material. In one embodiment, said resilient material includes synthetic rubber. Consequently, in one embodiment, an inward out mounted sealing member of the hydraulic brake sub sub-assembly is presented. According to one embodiment of the present invention, the sealing member at each end of the cylindrical structure is secured inwardly of the cylindrical structure in the manner such that it is secured to the inner periphery of the cylindrical bore and engaged by the engaging member into said plurality of the grooves provided at the inner periphery of the bore. As per one embodiment of the present invention, the inclusion of the sealing member in the inward out direction at each end of the cylindrical structure of the hydraulic brake sub-assembly helps in preventing damage to the sealing member during the servicing or assembling of the hydraulic brake sub-assembly on the brake drum.
[00029] Although the present invention has been exemplified for the
three-wheeled vehicle, it is not restricted only for the three-wheeled vehicle. Application of the present invention may be extended to other vehicles, including two-wheeled vehicles and four –wheeled vehicles.
[00030] Exemplary embodiment detailing features of the three-wheeled
vehicle, in accordance with the present invention will be described hereunder. The embodiments described herein apply to the three-wheeled vehicle powered by an internal combustion engine. However, the present invention is not restricted in its application and is also applicable to vehicles employing the drive motor or either by the internal combustion engine or the drive motor selectively or by the internal combustion engine alone.
[00031] The three wheeled automotive vehicle is mainly, but not solely, used
as a passenger carrier. It is to be noted that “front” and “rear”, and “left” and

“right” wherever referred to in the ensuing description, refer to front and rear, and left and right directions as seen in a state of being seated on a seat of the vehicle and looking forward. Furthermore, a longitudinal axis refers to a front to rear axis relative to the vehicle, while a lateral axis refers generally to a side to side, or left to right axis relative to the vehicle. Various other features of the three-wheeled vehicle according to the present subject matter here will be discernible from the following further description thereof, set out hereunder.
[00032] Fig. 1. illustrates a side perspective view of an exemplary
three-wheeled vehicle (10) (hereinafter “the vehicle”), in accordance with an embodiment of the present subject matter. In one embodiment, the vehicle (10) has the frame (not shown), which includes a head tube, a main tube extending rearward from the head tube. The vehicle (10) has a front cowl (13) positioned in the anterior portion of the head tube. A wind shield (12) is mounted to the front cowl (13). A floorboard (18) is extending from the bottom portion of the front cowl (13) to the rearward direction of the vehicle (10), supported by the main tube. A handle bar assembly (14) is rotatably supported by the head tube, positioned behind the front cowl (13). A front fender (15) is above the front wheel (16), covering at least a portion of the front wheel (16).A bottom portion of a body panel (21) is connected to the posterior portion of the floorboard (18). As per one embodiment, said pair of rear wheels (20) are connected to a swing arm through one or more suspension(s), the swing arm is in turn connected to the frame. The rear suspension includes a shock absorber and a suspension spring mounted to the frame. A hydraulic braking system of the three-wheeled vehicle (10) associated with a drum brake system includes a brake drum (24) attached to the front wheel (16) and said pair of rear wheel (20). A hood (11) connects a top portion of the front cowl (13) and a top portion of the body panel (21). The vehicle (10) is longitudinally divided into two portions along the line X-X’; a front portion has a driver’s seat (17) while a rear portion has at least one passenger seat (19) with a seating capacity of one or more passengers. The driver seat (17) is positioned in a posterior portion to a handle bar assembly (14). A seat base and a backrest form the driver seat. The driver operates the vehicle (10) in a

sitting position by sitting on the seat base. A partition wall is positioned along the line X-X’ extending in the lateral direction of the vehicle (10). The driver’s seat (17) comprises a seat base (17a) and a fixed backrest (17b).
[00033] Fig. 2. illustrates an enlarged plane view of the pair of rear wheels
(20) (only one shown) of the vehicle (10) with said hydraulic brake sub-assembly (100) disposed therein. According to the one embodiment of the present invention, the hydraulic braking system for the three-wheeled vehicle (10) comprises of said front brake unit being associated with said front wheel (16) and said rear brake unit associated with said pair of rear wheels (20). The brake drum
(24) of the drum brake system is fixedly attached to an inner surface of said front
wheel (16) and said pair of rear wheels (20). The hydraulic brake sub-assembly
(100) is disposed in the brake drum (24) and comprises of said cylindrical
structure (101) (shown in Fig.6) having the bore (111) formed therethrough.
[00034] Fig.3 illustrates the hydraulic brake sub-assembly (100) being
mounted on the backing plate (23) between the two brake shoes (22), (25) including a primary brake shoe (22) and a secondary brake shoe (25) as per one embodiment of the present invention. The drum brake system for the vehicle (10) includes the backing plate (23), the brake drum (24), two brake shoes (22), (25), the hydraulic brake sub-assembly (100) and various springs and pins. The hydraulic brake sub-assembly (100) is located in said front wheel (16) and said pair of rear wheels (20) and is usually positioned at the top of the wheel, above said two shoes (22),(25). In one embodiment, said hydraulic brake sub-assembly (100) exerts force onto the shoes (22), (25) so as to bring them into contact with the brake drum (24) and stop the vehicle with friction The brake drum (24) (shown in Fig.1 &2) includes said backing plate (23), said two brake shoes (22),
(25) slidably mounted on the backing plate (23), and the hydraulic brake
sub-assembly (100) supported on the backing plate (23) between contiguous ends
of said two brake shoes (22),(25). The hydraulic brake sub-assembly (100) is
located inside the brake drum (24) and is either bolted or firmly clipped to the
backing plate (23). A retaining clip attaches the hydraulic brake sub-assembly

(100) to the backing plate (23). The clip and the hydraulic brake sub-assembly (100) are attached to the backing plate (23) from the same side of the backing plate (23). The hydraulic brake sub-assembly (100) converts hydraulic pressure from a master cylinder assembly into mechanical force that pushes the brake linings against the inside of the brake drum (24). The brake drum (24) works when hydraulic brake fluid is forced the master cylinder to the hydraulic brake sub-assembly (100) that force said primary brake shoe (22) and said secondary brake shoe (25) out and against the surface of the brake drum (24). The hydraulic brake sub-assembly (100) expands the two brake shoes (22), (25) outward towards the inside of the brake drum (24). Further in Fig.3, as per one embodiment of the present invention, the hydraulic braking system for the three-wheeled vehicle (10) include the hydraulic brake sub-assembly (100) having two hydraulically actuated pistons (105) connected to corresponding said brake shoes (22),(25) which face the interior circumferential surface of the brake drum (24). The two pistons (105) respond to increase in hydraulic pressure caused by the actuation of the brake pedal and expand outwardly from the cylindrical structure (101) of the hydraulic brake sub-assembly (100) in opposite directions to displace the two brake shoes (22), (25) outwardly into frictional contact with the brake drum (24). An arrangement of springs (27), or the like, is utilized to return the two brake shoes (22), (25) and therefore the pistons (105), to their original positions once the hydraulic pressure is reduced. The master cylinder transmits hydraulic pressure to the hydraulic brake sub-assembly (100) when the pedal is pressed.
[00035] Fig.4 & Fig.5 illustrates said hydraulic brake sub-assembly (100)
being disposed between the primary brake shoe (22) and the secondary brake shoe (25) of the drum brake system. The hydraulic braking system in the three-wheeled vehicle (10) functions in decelerating and stopping said vehicle (10). In the hydraulic braking system for the three-wheeled vehicle (10), the front wheel 16 and said pair of rear wheels 20 are provided with the brake drum (24). As per one embodiment of the present invention, the hydraulic brake sub-assembly (100) is disposed between the two brake shoes (22), (25). The brake drum (24) associated with the front wheel (16) and said pair of rear wheels (20) of the three-wheeled

vehicle (10) has typically two brake shoes (22), (25) pivotally mounted to the backing plate (23) (shown in Fig.3). In the hydraulic brake sub-assembly (100), said sealing member (106) is provided which is urged against the inwardly facing end surface of the two pistons (105) by said spring (107).
[00036] Fig.6 illustrates a perspective view of the hydraulic brake
sub-assembly (100). According to the invention, said cylindrical structure (101) of the hydraulic brake sub-assembly (100) comprises of the first hollow cylinder (101a) (shown in Fig.8) and the second hollow cylinder (101b) (shown in Fig.8) and said first hollow cylinder (101a) and said second hollow cylinder (101b) firmly attached together through press-fitting to form one complete said cylindrical structure (101).As per one embodiment of the present invention, the hydraulic brake sub-assembly (100) is fitted with a bleeder screw (108) and a inlet port (112) for the entry of the brake fluid (112). The bleeder screw (108) allows for bleeding of air and old brake fluid from the hydraulic brake system. The cylindrical structure (101) of the hydraulic brake sub-assembly (100) response to an increase in hydraulic pressure and expands axially outwardly in opposite directions to displace the two brake shoes (22) and (25) outwardly.
[00037] Fig.7 shows a perspective exploded view illustrating one end (102) of
the hydraulic brake sub-assembly (100). As per one embodiment of the present invention, the hydraulic brake sub-assembly 100 usually contain the cylindrical structure (101) , said two pistons (105), the seal cups (104) for each piston (105), the spring (107) and expander set, the sealing member (106) for each open end (102) of the cylinder, a pushrod for each piston (105), and the bleeder screw (108). Further in Fig.7, as per one embodiment, the hydraulic brake sub-assembly (100) with seal cups (104) and said sealing member (106) is secured inwardly into said plurality of grooves (109) (shown in Fig.8) provided on inner periphery of the cylindrical structure (101). As per one embodiment of the present invention, the cylindrical structure (101) includes the first hollow cylinder (101a) and the second hollow cylinder (101b) in the manner that the first hollow cylinder (101a) of the cylindrical structure (101) is made up of cast iron or plastic and the second hollow

cylinder (101b) made up of aluminium material.The bleeder screw (108) fitted to the hydraulic brake sub-assembly (100) to allows for bleeding of air and old brake fluid from the hydraulic brake system. The bleeder screw (108) is a hollow screw. It has a taper on the end that mates with a matching tapered seat in the cylindrical structure (101). The bleeder screw (108) has been cross-drilled into the center hole just above the taper. This way, when the bleeder screw (108) is loosened slightly, the tapered seat opens and brake fluid enters the cross-drilled passage into the center hole and flows out the end of the bleeder screw (108).
[00038] Fig.8 illustrates an exploded sectional view of the hydraulic brake
sub-assembly in Fig.7. As per one embodiment of the present invention, the hydraulic brake sub-assembly (100) comprises of said cylindrical structure (101) comprising of said first hollow cylinder (101a) and said second hollow cylinder (101b), said spring (107) extends between the two pistons (105) to normally force them axially inwardly, said two pistons (105) are disposed in the bore (111) of the cylindrical structure (101) of the hydraulic brake sub-assembly (100) and are adapted to slide in the bore (111). As per one embodiment of the present invention the sealing member (106) extends over the respective ends (102) of the cylindrical structure (101) of hydraulic brake sub-assembly (100) along with the seal cups (104). Further in Fig.8, said sealing member (106) is secured inwardly into said plurality of grooves (109) provided on inner periphery of the cylindrical structure (101).
[00039] Fig. 9 shows a perspective exploded view illustrating both end of the
hydraulic brake sub-assembly (100). As per one embodiment of the present invention the cylindrical structure (101) of the hydraulic brake sub-assembly (100) comprises of the first hollow cylinder (101a) and the hollow second cylinder (101b). The first hollow cylinder (101a) and the second hollow cylinder (101b) are firmly attached together through press-fitting to form a single cylindrical structure (101). The hydraulic brake sub-assembly (100) comprises of said sealing member (106) provided at both the ends (102) of said cylindrical structure (101) and said sealing member (106) is secured inwardly to an inner

periphery of said cylindrical structure (101) through said engaging member (103). In one embodiment of the present invention, the engaging member (103) that is the circular retainer plate comprises of a plurality of retaining slots (103a) (shown in Fig.8) being adapted into plurality of grooves (109) provided on said inner periphery of said cylindrical structure (101). The spring (107) extends between the two pistons (105) to normally force them axially outward. The bleeder screw (108) and the inlet port (112) for the entry of brake fluid are fitted with the hydraulic brake sub-assembly (100). The bleeder screw (108) has a small rubber dust cap (110) that fits over the exposed end of the bleeder screw (108) to keep water, dirt, and debris from entering the center hole and plugging it up or rusting it in place. Further in Fig.9, as per one embodiment of the present invention the sealing member (106) is secured inwardly into plurality of grooves (109) (shown in Fig.8) provided into the inner periphery of the cylindrical structure (101) by said engaging member (103) that is the circular retainer plate. The sealing member (106) provided at each end (102) of the cylindrical structure (101) of the hydraulic brake sub-assembly (100) and being secured inwardly into the plurality of grooves (109) through the engaging member (103). The engaging member (103) that is the circular retainer plate secures the sealing member (106) in the manner as to prevent the axial displacement of the sealing member (106) on impact from any cyclic load. As per one embodiment of the present invention, the hydraulic brake sub-assembly (100) includes said seal cup (104) provided on each piston (105) to prevent the leakage of fluid, the engaging member (103) and the sealing member (106) are provided at both the ends (102) of the cylindrical structure (101). The cylindrical structure (101) of the hydraulic brake sub-assembly (100) comprises of the said first hollow cylinder (101a) and said second cylinder as (101b). The second hollow cylinder (101b) is press-fitted into the first hollow cylinder (101a) to make one complete cylindrical structure (101) in the manner that the outer periphery of the cylindrical structure (101) will be made of cast iron or plastic and inner periphery will be with aluminium lining.
[00040] Fig.10 shows a front view the hydraulic brake sub-assembly (100).
As per one embodiment of the present invention, the hydraulic brake

sub-assembly (100) is disposed on the brake drum (24) and comprises of said cylindrical structure (101) and the bleeder screw (108) having said small rubber dust cap (110).
[00041] Fig.11 shows a sectional view of the hydraulic brake sub-assembly
(100) along a longitudinal plane. According to one embodiment of the present invention, the engaging member (106) that is the circular retainer plate made up of metal or plastic. The sealing member (106) is designed to protect the hydraulic brake sub-assembly (100) from entry of dust, mud and water entry, and as a secondary protection against immediate leakage of brake fluid out from the hydraulic brake sub-assembly (100). These are components that are subject to continuous cyclic load. The sealing member (106) of the hydraulic brake sub-assembly (100) expands and contracts under the continuous back and forth axial displacement of the two pistons (105).
[00042] Fig.12 shows a side view of the hydraulic brake sub-assembly (100).
In one embodiment of the present invention, the cylindrical structure (101) comprises of the first hollow cylinder (101a) made up of cast iron or plastic and the second hollow cylinder (101b) of aluminium material in the manner that the outer surface or the periphery of the cylindrical structure (101). As per one embodiment of the present invention, the second hollow cylinder (101b) is having a diameter smaller than that of the first hollow cylinder (101a) and is press-fitted into the first hollow cylinder (101b).
[00043] Fig.13 illustrates a sectional view of said hydraulic brake
sub-assembly (100) along a transverse plane. As per one embodiment of the present invention, said first hollow cylinder (101a) and said second hollow cylinder (101b) of the cylindrical structure (101) of said hydraulic brake sub-assembly (100) are firmly attached together through press-fitting. The sealing member (106) provided at both ends (102) of said cylindrical structure (101) is secured inwardly to the inner periphery of said cylindrical structure (101) through said engaging member (103). According to one embodiment of the present invention, the sealing member (106) is secured inwardly to said cylindrical

structure (101) in a manner that said sealing member (106) is mounted in the inward-out manner onto both ends (102) of the cylindrical structure (101). As per one embodiment of the present invention, the adapting of said sealing member (106) on the inner surface of the cylindrical structure (101) is to endure cyclic load resist sudden impact load and hence improving the durability of the hydraulic brake sub-assembly (100).
[00044] It is advantageous to have the modified hydraulic brake sub-assembly
for the hydraulic braking system which comprises of said improved sealing member being secured inwardly to the cylindrical structure. Such design of the sealing member being provided at each end of the cylindrical structure of the hydraulic brake sub-assembly improves the durability of the hydraulic brake sub-assembly by protecting the brake fluid from being contaminated by the dust or moisture. Further, it is advantageous to have a modified cylindrical structure for the hydraulic brake sub-assembly which includes the first hollow cylinder and the second hollow cylinder such that the second hollow cylinder is press-fitted into the first hollow cylinder. Thus, preventing the cylindrical structure of the hydraulic brake sub-assembly from corrosion and rusting.
[00045] Improvements and modifications may be incorporated herein without
deviating from the scope of the invention.

We claim:
1. A vehicle (10) comprising:
a front wheel (16) and a pair of rear wheels (20);
a brake drum (24) fixedly attached to an inner surface of said front wheel (16) and said pair of rear wheels (20); and
a hydraulic brake sub-assembly (100) disposed in said brake drum (24), said hydraulic brake sub-assembly (100) comprising a cylindrical structure (101) having a bore (111) formed therethrough;
characterized in that said cylindrical structure (101) comprises of a first hollow cylinder (101a) and a second hollow cylinder (101b).
2. The vehicle (10) as claimed in claim 1, wherein said first hollow cylinder (101a) and said second hollow cylinder (101b) are firmly attached together through press-fitting.
3. The vehicle (10) as claimed in claim 1, wherein said hydraulic brake sub-assembly (100) comprises of a sealing member (106) provided at both ends (102) of said cylindrical structure (101).
4. The vehicle (10), as claimed in claim 3, wherein said sealing member (106) provided at both ends (102) of said cylindrical structure (101) is made up of a resilient material.
5. The vehicle (10) as claimed in claim 4, wherein said sealing member (106) is secured inwardly to an inner periphery of said cylindrical structure (101) through an engaging member (103).
6. The vehicle (10) as claimed in claim 5, wherein said engaging member (103) is a circular retainer plate made up of metal and plastic.
7. The vehicle (10) as claimed in claim 6, wherein said engaging member (103) comprises of a plurality of retaining slots (103a), (103b) being adapted into a plurality of grooves (109) provided on said inner periphery of said cylindrical structure (101).

8. The vehicle (10) as claimed in claim 1, wherein said first hollow cylinder (101a) is made up of a cast iron and said second hollow cylinder (101b) is made up of an aluminium alloy.
9. The vehicle (10) as claimed in claim 1, wherein said first hollow cylinder (101a) is made up of a resin material and said second hollow cylinder (101b) is made up of an aluminium alloy.
10. The vehicle (10), as claimed in claim1, wherein said second hollow cylinder (101b) having a diameter smaller than that of the first hollow cylinder (101a) is press-fitted into the first hollow cylinder (101a).