This invention relates to an automotive drum brake system with provision for enhanced cooling.

Brakes are important safety components. Both disc and drum brake work on the same principle: friction and heat. When resistance or friction is applied to a turning wheel, the vehicle's brake system causes the wheels to decelerate and finally stop. During this process heat is generated causing the brake temperature to rise. The factors, which determine the vehicle deceleration, are vehicle weight, braking force, coefficient of friction, and pressure distribution over the braking surface area. Apart from these, another important factor is how efficiently the brake system converts the wheel motion into heat and subsequently, how quickly this heat is dissipated from the brake components. Disc brake components are fully exposed to the atmosphere and hence heat removal is efficient. On the other hand, drum brake components are fully enclosed inside the brake assembly. This may result in comparatively higher temperature vis-a-vis disc brake system under same braking conditions. High temperature of the drum brake shoe may cause brake fade and eventually lose effectiveness. Fading is the result of too much heat build-up within the drum. Hence, the drum brakes can only operate as long they can absorb heat generated by kinetic energy lost due to decelerating the wheels. Once the brake components are themselves become saturated with heat, they lose the ability to stop a vehicle.

At high temperatures, other components of the brake system undergo higher thermal expansion. Since the geometry of the drum brake is more complicated than the disc brake, maintaining the component dimensions at high temperature within the desirable limit is very critical. Thermal expansion of a component beyond a certain limit may interfere with the other neighboring components. This may result in the thermal seizure or locking of the drum brake. This, in turn, can result in further rise in temperature of the system and consequently, it can trigger the failure of other components.

In steady state, there is a balance between heat conduction from the drum to the convection to the ambient air. Following equation expresses heat energy balance.

-KA1 dt/dx=Ha2Dt (1)

where K is the material conductivity, Ai is the brake drum area, A2 is the hub area. It is clear from the above formula that a higher conducting material is needed for efficient heat conduction from the drum brake area. Presently aluminum casting is used as a medium for heat dissipation from the brake drum to the air. However, owing to its low thermal conductivity, heat dissipation happens at slower rates. Hence, a high conducting material in combination with aluminum is desirable to improve the drum brakes thermal performance.

In summary, a high rate of heat generation inside the drum brakes and low dissipation of heat to the ambient air leads to the following failures:

• Brake fading
• Squeal noise

• Ineffective braking

• Reduced life of liner and drum

The challenge for brake designers is to design a brake system that would dissipate heat generated inside the drum as quickly as possible to the ambient.

The automotive drum brake system with provision for enhanced cooling, according to this invention, comprises at least one high conducting material inserted in the aluminum alloy wheel such that a portion of the material touches the cast iron drum liner, the other part of the high conducting material being exposed to atmosphere for dissipation of heat, to cause reduction in heat of the drum liner.

As discussed above, effective and quick removal of heat dissipation from the brake drum is desirable. In this invention, a novel way of dissipating the heat quickly from the brake drum liner to the ambient is presented. A high conducting material along with the combination of aluminium and/or magnesium casting is used for efficient removal of heat from the brake drum directly to the ambient air. There are many materials of higher conductivity than that of aluminium like Gold,

Copper, Silver, Diamond, Graphene and Graphite. Following table lists the values of thermal conductivity of materials of higher thermal conductivity than aluminium.

Material name Thermal conductivity (/c), W/(m-K)

Aluminium alloy 120-180

Gold 3T8

Copper 401

Silver 429

Diamond 900-2320

Graphene 4840-5300

Graphene is a one-atom-thick planar sheet of sp-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. As of 2009, graphene appears to be one of the strongest materials ever tested. Measurements have shown that graphene has a breaking strength 200 times greater than steel However, the process of separating it from graphite, where it occurs naturally, will require some technological development before it is economical enough to be used in industrial processes

Graphite {k=27Q W/m-K) is another higher thermal conductivity material than aluminum. Results (table 1) show that when a high conducting material is used along with the standard aluminum alloy, temperature of the drum liner reduces and this is desirable. This also results in the reduction of temperature gradient. A higher conducting material like Graphene would further result in reduction of the drum liner temperature.

Table 1. Temperature gradient comparison with Aluminium alloy and graphite insert.

Drum liner temperature(max) Temperature gradient (drum liner to ambient air)

Aluminium alloy 276 246

Aluminium alloy + Graphite
260 230

insert

The high conducting material has to be designed and placed in such a way that heat removal from the heat generating zone i.e. drum liner is maximum. This aspect of invention is described in the following section.

Figure 1. Prior art representation of drum brake cooling system. Heat is generated between the interface of asbestos liner 2 and cast iron liner 3. A part of this heat generated is dissipated thought the aluminium alloy wheel 4.

Figure 2. One aspect of invention showing the cross section of the drum brake system. A high conducting material 5 is embedded into aluminium wheel hub area. The number of conducting material embedded into the system can vary depending upon the cooling requirement.

Figure 3. Another aspect of invention showing different design of the high conducting material embedded into the wheel hub

Figure 1 shows the line diagram of a cut section of the prior art in drum brake. Asbestos liner 2 forms a part of the Aluminum brake shoe 1. On brake application the asbestos liner 2 rubs the cast iron drum 3, which generates heat due to friction. The heat generated is conducted through the Aluminum alloy wheel 4 and dissipated to the ambient through the air and Aluminum alloy wheel arm 4A. Slower the heat dissipation, larger will be the temperature rise of the asbestos and drum liner.

Figure 2 shows one aspect of the invention for faster removal heat from the drum liner to the ambient. A high conducting material 5 e.g. graphite is inserted in the aluminum alloy wheel 4 in radial direction in such a way that it touches the cast iron drum liner 3. The shape and sizes of the insert can vary depending on the structural and thermal requirements of the drum brake. Since the high conducting material is in direct contact with the drum liner where temperature is high, conduction heat transfer is higher. Other part of the high conducting material 5 is exposed to the atmosphere where heat is dissipated by convection to air. This results in decrease in temperature of the drum liner as indicated in the table 1. The number of inserts in the aluminum alloy wheel 4 would depend on the temperature uniformity and temperature reduction required inside the drum brake liner.

Figure 3 shows another aspect of the invention for drum liner temperature reduction. The high conducting material is inserted in the aluminum alloy wheel in the form of a ring 6 touching the drum liner. The insert 5 described in figure 2 forms an integral part of the ring. The mechanism of heat transfer is similar as described in figure 2. The advantage of this design of high conducting material is that uniform temperature distribution would be achieved in the drum liner, which would increase the thermal performance of the brake.

It will be appreciated that various other embodiments of this invention are possible without departing from the scope and ambit thereof.

We Claim:

1. An automotive drum brake system with provision for enhanced cooling comprising at least one high conducting material inserted in the aluminum alloy wheel such that a portion of the material touches the cast iron drum liner, the other part of the high conducting material being exposed to atmosphere for dissipation of heat, to cause reduction in heat of the drum liner.

2. An automotive drum brake system as claimed in Claim 1 wherein the high conducting material includes graphite.

3. An automotive drum brake system as claimed in Claim 1 or Claim 2 wherein the high conducting material is inserted in the said wheel in a radial direction.

4. An automotive drum brake system as claimed in Claim 1 wherein the said material in the form of a ring is inserted in the said wheel touching the drum liner.

5. An automotive drum brake system with provision for enhanced cooling substantially as herein described with reference to, and as illustrated in, the accompanying drawings.