Drum Brake Arms

FIELD OF THE INVENTION

The present invention relates to drum brake arms and more particularly to arms of a brake drum in a wheel for use in a two wheeled or a four wheeled vehicle.

BACKGROUND OF THE INVENTION

In some vehicles such as a scooter type motorcycle, the centre of either wheel is generally provided with a drum brake system comprising mainly of a brake drum, brake panel with retractable brake shoes and brake liner along with other components, to bring the moving vehicle to rest or to slow down the speed of vehicle on operation of the drum brake system. The brake panel (with brake shoes) is nested inside the brake drum to develop into a wheel hub in such a way that when the vehicle wheel rotates, the brake drum rotates along with the vehicle wheel and the brake panel remains static. Further the outer surface of the brake drum is connected to a rim of the said wheel through radial elongated projections referred hereto as brake drum arms.

Generally braking in such a drum brake system is achieved by manually operating a brake control lever on the vehicle handle bar resulting in pressing of brake shoes of the brake panel against the inner surface of the rotating brake drum. The friction thus produced between the brake shoes and the brake drum causes the wheel to decelerate and finally stop. This process is associated with generation of significant amount of thermal energy inside the wheel hub causing the rise in overall temperature of the brake drum. Therefore it is critical to keep the ambient temperature within the operable limit inside the brake drum.

Further, at high temperatures, other components of the drum brake system undergo thermal expansion. Since the construction and geometry of a drum brake system is more complicated than a disc brake system, maintaining the component dimensions' at high temperature within the desirable limit is critical. Thermal expansion of a component beyond the desirable limit may cause it to interfere with other neighbouring components. This may result in the thermal seizure or locking of the drum brake system leading to further rise in temperature of the system and consequently, it can trigger the failure of other components.

Hence any excess temperature or heat build-up within the brake drum will cause significant decrease in braking efficiency leading to ineffective braking while consequently resulting in other known effects like brake fade. It also causes reduction in life of brake shoe, brake liner and the brake drum. Therefore the braking efficiency of drum brake system depends on how quickly the generated heat is dissipated from the brake drum.

The prior art as shown in Figure 1 (a) and 1 (b) shows a drum brake system made of steel alloy where a part of heat generated in the inner surface 206 of the brake drum 203, nesting in the brake panel (not shown) with retractable brake shoes, is dissipated towards its outer surface 205 on which brake drum arm(s) referred by numeral 202, rest. A part of heat is also conducted to the brake drum arms 202 from the outer surface 205 of the brake drum 203. The said arms 202 are spaced in between to allow air cooling of the heated brake drum 203.

It can be seen from the figure that the width of the brake drum arms 202 is aligned more toward the vehicle longitudinal axis and less toward the vehicle lateral axis. This construction of arms in the prior art drum brake system does not provide lateral stiffness to the wheel 110 due to which the strength of the rim 201 remains weak in lateral direction. Failures such as bending have been observed in such designs.
Furthermore, welding of brake drum arms 202 on the outer surface of the brake drum 203 near to the heat generation area is difficult due to which the said arms are welded at some distance "A" from this area as is evident from the Figure 1(c). As the arms are located away from heat generation area the heat dissipation is inefficient. Therefore this design of brake drum arms 202 does not contribute much to the heat dissipation from the brake drum 203 resulting in high brake drum temperature. The present problem becomes more severe when drum brake system is fabricated from a less conducting material like steel. However for manufacturing purposes, using a sheet metal brake drum is advantageous on account of comparative cost reduction and easier welding but leads to substantial reduction in heat dissipation from the brake drum surface. Therefore the challenge is to design a brake drum with brake drum arms fabricated of steel leading to better heat dissipation than the prior art.

The present invention is directed to overcoming one or more problems as set forth above.

SUMMARY OF THE INVENTION

It is hence an object of the present invention to disclose a brake drum for a motorcycle comprising a plurality of brake drum arms for better heat dissipation to keep the temperature inside the brake drum within the operable limit, and also leading to enhanced structural stiffness of the wheel in the lateral direction. To this end, the subject matter described herein, in accordance with an embodiment of the present subject matter thereof, relates to a wheel for a motorcycle comprising a brake drum, a wheel rim and atleast one brake drum arm radially extending from the said brake drum to the said rim such that the width of said brake drum arm is substantial in the lateral direction. According to an embodiment of the present invention, the present subject matter is suited, preferably to a wheel wherein the said brake drum is fabricated from a less conductive material including steel.

Another aspect of the present invention is to disclose an improved brake drum comprising brake drum arms wherein the brake drum arms impart better stiffness to the wheel rim. To this end, the drum brake arm according to the present subject matter is a continuous arm, with atleast two arms connected at one of their surfaces, connecting the brake drum and the wheel rim.

The foregoing objectives and summary provide only a brief introduction to the present subject matter. To fully appreciate these and other objects of the present subject matter as well as the subject matter itself, all of which will become apparent to those skilled in the art, the ensuing detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. However, it should be understood that the detailed description while indicating preferred embodiment(s) of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features, aspects, and advantages of the subject matter will be better understood with regard to the following description, appended claims and accompanying drawings where:

Figure 1 depicts various views of a wheel of a vehicle with a brake drum showing the construction of brake drum arms according to the prior art.

Figure 2 shows a side view of an embodied vehicle in the form of a scooter type motorcycle capable to accommodate the present invention.

Figure 3(a) shows an isometric view of a brake drum with brake drum arms connected to a wheel rim according to an embodiment of the present invention. Figure 3 (b) shows an isometric view of the said brake drum without wheel rim.

Figure 4(a) and 4(b) respectively show an isometric view and a front view of a brake drum arm according to an aspect of the present invention.

Figure 5(a) and 5(b) show an isometric view and a front view respectively of another embodiment of the brake drum arms according to the present invention wherein a smaller brake drum arm is placed insider a bigger brake drum arm connected to the outer surface of the brake drum.

Figure 6 illustrates yet another embodiment of the present invention comprising of brake drum arms resting on the brake drum.

DETAILED DESCRIPTION OF THE INVENTION

The subject matter described herein relates to a brake drum comprising of brake drum arms connecting the brake drum to a wheel rim for better heat dissipation and structural stiffness of the wheel. Various other features of the brake drum arms according to the present invention here will be discernible from the following further description thereof set out hereunder.

In the ensuing exemplary embodiments, the vehicle is a scooter type motorcycle. However it is contemplated that the disclosure in the present invention may be applied to any automobile capable of accommodating the present subject matter without defeating the spirit of the invention. Further "front" and "rear", and "left" and "right" referred to in the ensuing description for the illustrated embodiment 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.

The present invention is now described in detail in connection with the rendered drawings. It should be noted that like elements are denoted by the same reference numerals throughout the description. The detailed explanation of the constitution of parts other than the invention which constitutes an essential part has been omitted at opportune places.

Figure 2 shows a side view of a typical scooter type motorcycle (vehicle) capable to accommodate the present invention. Typically such a vehicle includes a body frame assembly made up of several tubes welded together which usually supports the body of the said vehicle. The frame assembly 101 of the scooter type motorcycle is an elongated structure, which typically extends from a forward end to a rearward end of the vehicle. It is generally convex in shape, as viewed from a side elevational view. The said frame assembly 101 includes a main frame and may also have a sub-frame. The sub-frame is attached to the main frame using appropriate joining mechanism. The frame assembly 101 includes a head tube and a down tube that extends downward from head tube. The frame assembly is covered by a plurality of vehicle body covers including a front panel 115, a leg shield 116, an under seat cover 117 and a side panel 112.

A handlebar assembly 105 and a seat assembly 106 are supported at opposing ends of the frame assembly and a generally open area is defined there between known as floorboard 107 which functions as a step through space. A fuel tank that stores fuel that is supplied to the engine is disposed at the rear end of the vehicle above the rear wheel. It is present on the upper side of the power unjt along with a fuel tank cap. The seat for a driver and a pillion is placed forward to the fuel tank (not shown) and rearwardly of the floorboard 107.

The vehicle has a steerable anterior wheel 110 and a driven rear wheel 111 driven by driving force generated by a power unit. A muffler (not shown) is provided to the right side of the rear wheel 111, and connects to the engine. A side stand fixed to the left side of the body frame supports the vehicle such that vehicle inclines to the left side.

Typically, front 103 and rear 114 suspension assemblies are operatively positioned between the front 110 and rear 111 wheels and the frame assembly. The front suspension assembly 103 commonly is a telescopic fork arrangement while the rear suspension assembly 114 is a hydraulic damped arrangement.
In the said vehicle, the rear suspension swing arm typically supports the power unit which is configured to drive the rear wheel 111 of the vehicle. The power unit is structured such that an engine 102 and a swing case 108, which are well known for this form of the vehicle, are integrally constructed. In an embodiment of the present invention, the engine is a four stroke single cylinder engine and the swing case 108 is connected to a left side surface of a crankcase of the engine 102 so as to extend forward.

It is disposed on the vehicle frame with one end of the swing case 108 attached to the rear wheel hub in such a way that the power unit is substantially angularly disposed to the ground. The engine 102 is arranged horizontally, that is, its crankshaft is placed at right angles to the longitudinal direction of the vehicle body. Since the basic construction of an engine is known to those versed in the art, the details have been omitted. The said power unit is surrounded by a shroud or a covering with a fan to enhance forced cooling of the power unit. This covering present over the power unit is known as cooling cowl (not shown) and may be made of plastic resin or the likes.

The said vehicle is capable of accommodating the present invention is either or both of its wheels. Figure 3(a) shows an isometric view of a brake drum in the wheel according to the present invention. The anterior wheel 110 capable of rotating along the wheel axle 204 comprises of a wheel rim 201 present at the circumference of the wheel 110. Further a drum brake system is positioned at the centre of the wheel for effective braking. The anterior wheel 110 consists of a brake drum 203 at its centre. The said brake drum has two surfaces, namely an outer surface 205 facing towards the wheel rim 201 and an inner surface 206 facing towards a brake panel (not shown) with retractable brake shoes.

The brake drum 203 comprises of at least one brake drum arm 202 on its outer surface 205. The said arm 202 connects the brake drum 203 to the wheel rim 201 and helps in load distribution around the anterior wheel 110. According to an embodiment of the present invention, the brake drum 203 comprises of multiple brake drum arms together referred to by the numeral 202. The brake drum arms 202 are connected to the brake drum 203 in such a way that the arm width of each of the arms 202 is along the vehicle lateral axis unlike the prior art. Thus the arms connect the brake drum 203 and the rim 201 mainly in lateral direction. This construction increases the structural stiffness of the wheel rim in the lateral direction due to increase in the contact area. The detailed construction of the brake drum arms without the wheel rim is shown in Figure 3(b).

Figure 4(a) shows an isometric view of a brake drum arm 202 according to an aspect of the present invention. The entire structure of a brake drum arm 202 approximately resembles a "U" shape structure. The brake drum arm 202 loosely comprises of two projections facing each other joined by a base between them. This base completely covers the outer surface 205 of the brake drum 203 over which it is rested. Thus the area of the said base is identical to the area of the outer surface of the brake drum it covers. The said base is curved and acts as a drum-arm interface 208. The head of both projections face toward each other and form rim-arm interface 207. Thus each brake drum arm 202 as shown in Figure 4(a) has at least one drum-arm interface 208 and at least two rim-arm interfaces 207. Both the projections of each brake drum arm are in contact with other projections proximate to them.

Adjacent brake drum arms are in contact with each other through one of their projections. The entire construction of brake drum arms is such that when located, they are connected to the outer surface 205 of the brake drum 203 on one side and to the wheel rim 201 on the other side. At any point of time thus, each brake drum arm 202 is in contact with the wheel rim 201, brake drum 203 and to adjacent brake drum arm(s) close to it. In a preferred embodiment the said brake drum arms 202 are connected with the outer surface 205 of the brake drum 203 by welding or casting near the heat generation area. The covering of outer surface of brake drum by the base of the brake drum arm leads to faster heat dissipation during braking unlike the prior art.

Further the base of the brake drum arm is continuous and helps in faster heat conduction from the brake drum to the brake drum arm(s). Many different combinations of such construction are possible, one of which is shown in Figure 5(a) and 5(b) in isometric and front views respectively. A smaller arm 209 is placed over the larger brake drum arm 202 thus providing four contact points with wheel rim 201. This embodiment provides high strength to the wheel rim and efficiently conducts heat from the brake drum to the brake drum arms through the said base.

Figure 6 shows another embodiment of the brake drum arms wherein the base of the brake drum arm is not continuous. Adjacent brake drum arms 202a and 202b are placed side by side. However the base or the drum-arm interface 208 is not continuous leaving the surface exposed to air cooling.

The operation of the brake drum during braking operation is now explained. During the braking of the vehicle, heat generated inside the brake drum on account of friction between the rotating brake drum and static brake shoes is conducted by the brake drum material from the brake drum inner surface to the brake drum outer surface from where it travels to the drum-arm interface. A part of this heat is then conducted along the length of the brake drum arm from where it is dissipated to the environment with the help of air. All the brake drum arms work simultaneously thus ensuring better heat dissipation.

It will be appreciated that the present subject matter and its equivalent thereof offers many advantages, including those which are described henceforth. The above construction facilitates placing of more number of brake drum arms together on the outer surface of the brake drum than the prior art. More brake drum arms lead to more surface area leading to faster and better heat dissipation during braking than the prior art.

Further the present invention also imparts structural strength to the wheel rim in the lateral direction.

Furthermore, the present invention is preferably suited for brake drums fabricated from a sheet metal wherein the said brake drum arms, also preferably made of sheet metal, can be welded easily. During testing, it was found that the present invention leads to 50 degrees Celsius reduction In temperature of the brake drum when compared with the prior art. This reduction in the temperature is substantial and may lead to increase in life of the brake drum and other components inside the wheel hub and may reduce failures.

The present invention is thus described. The above description explains the present invention with respect to the anterior wheel of the vehicle. However the said invention can also be applied to rear wheel or both wheels of the vehicle. Further, the terms and expressions in this specification are of description and not of limitation and do not exclude any equivalents of the features illustrated and described, but it is understood that various other embodiments, modifications, substitutions, changes and equivalents are also possible without departing from the scope and ambit of the present invention which will now become apparent to those skilled in the art from this detailed description. Accordingly, the description is to be understood as an exemplary embodiment and reading of the invention is not intended to be taken restrictively.

We claim:

1. A brake drum at the centre of a vehicle wheel with a wheel rim for better heat dissipation during braking operation and better structural stiffness of the wheel, the said brake drum having an inner surface
and an outer surface, the said brake drum comprising of at least one brake drum arm on its outer surface extending from the brake drum to the wheel rim in radial direction, the said brake drum arm
having more width along the lateral axis of the vehicle wherein,

one end of the said brake drum arm is connected to the wheel rim through a rim-arm interface; another end of the brake drum is connected to the outer surface of the brake drum through a drum-arm interface and the brake drum arm approximately having a U shape structure.

2. The brake drum as claimed in claim 1, wherein the said drum brake arm is a continuous arm with atleast two brake drum arms welded together between the said brake drum and the said wheel rim.

3. The brake drum as claimed in claim 1, wherein the said drum brake and the said drum brake arm may be fabricated of any material including steel, the said drum brake arm connected to the brake drum preferably by welding or casting.

4. The brake drum as claimed in claim 1, wherein the said vehicle may be any automobile including a scooter type motorcycle.

5. A brake drum substantially as claimed in any of the preceding claims and illustrated with reference to the accompanying drawings.