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

A disc brake is a kind of braking device as a vehicle component whereby frictional heat is generated by forcing brake pads against both sides of disc (hereinafter called the disc rotor) rotating together with a wheel so that kinetic energy is converted into thermal energy to produce a braking affect. The engagement between the brake pads and the rotor is a frictional relationship that converts the kinetic energy of the moving vehicle to thermal energy. As a result of this energy conversion, the friction generates a significant amount of heat each time the brake pads are applied to the rotor. The temperature of the rotor can rise significantly following frequent frictional contact between the brake pads and the rotor. Under high temperature condition, rotor gets damaged. Also brake failure can happen if the rotor is not able to dissipate heat quickly. To provide a cooling effect to brake rotors, vents are placed within the rotor. The prior art includes several examples of these vented disc brake rotors. These rotors dissipate heat generated by the friction between the brake pads and the rotor by tunneling air through the vents and allowing the air to absorb a portion of the generated heat. This absorption takes away from the total heat absorbed by the brake rotor, thereby reducing the temperature of the rotor. The cooling capacity of the vents mainly depends on two factors: (a) quantity of air flowing through them and (b) surface temperature of the vents through which air passes. Prior art contains numerous examples of vent designs to increase the quantity of air and to increase heat transfer from vents to air.
In the past, disc rotors were mainly made of cast iron but in recent years, efforts to develop disc rotors of different materials have been tried. For example, the use of aluminum metal matrix composite (AL-MMC) in disc brakes has been reported, but it has been limited to its inability to withstand excessive temperatures. Furthermore, disc rotors made of carbon ceramics (carbon fiber reinforced silicon carbide or C/Sic) have also been developed because carbon ceramic is advantageous in terms of weight, heat resistance, and abrasion resistance. However, C/Sic disc rotors have a problem that the mechanical stress applied to them during braking may cause cracking. This mechanical stress is combination of two types of stress: pad pressure stress and stress generated by the torque applied to the disc rotor through disc rotor surface. The second stress is basically due to surface contact between the disc rotor and pad. Due to these and other defects of the prior art, there is a need for a vented disc rotor that enables high heat transfer for effective braking. The present invention provides a vented disc brake rotor that has vents with different material with higher thermal conductivity from the rotor steel materials. The ambient cold air passes through the vents, absorbs higher amount of heat generated by the frictional contact between the rotor and brake pad in the disc braking system. Furthermore, the design of vents is such that the pad does not come into contact with vent hole directly thus reducing the surface stresses. In this invention, a novel way of dissipating the heat quickly from the rotor to the ambient is proposed. A high conducting material for vents along with the combination of steel rotor is used for efficient removal of heat from the brake drum directly to the ambient air. There are many higher conducting materials than aluminium like Gold, Copper, Silver, Diamond, Graphene and Graphite. Following table lists the values of thermal conductivity of materials that have • higher thermal conductivity than aluminium.
Material name Thermal conductivity (k), W/(m-K)
Aluminium alloy 120-180
Gold 318
Copper 401
Silver 429
Diamond 900-2320
Graphene 4840-5300

Graphene is a one-atom-thick planar sheet of bonded carbon atoms that are densely packed in a honeycomb crystal lattice. As of the year 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=270 W/m-K) is another higher thermal conductivity material than aluminium. Results (table 1) show that when a high conducting material is used along with the standard aluminium 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 disc temperature. Results are shown in table 1, which shows temperature reduction of the disc rotor due to use of graphite. The maximum temperature is located at the interface between the rotor and pad. The reduction in temperature was possible due to higher temperature of vent holes compared to the prior art vents. Note that this value of temperature reduction would vary depending upon the shape, size and vent materials.

Table 1. Temperature gradient comparison with AISI 410 and graphite insert.

Disc
temperature (max)
AISI 410 355
AISI 410 +graphite insert 335

This invention will now be described with reference to the accompanying drawings, which illustrate in

Figure 1: Prior art representation of disc brake cooling system. Heat is generated between the interface of pad 1 and rotor surface 2. A part of this heat generated is dissipated to the ambient air though vents 3.

Figure 2: One embodiment of this invention (by way of example and not by way of limitation) showing the disc brake system with vents 4 inserted with higher thermal conductivity materials. The number of vents embedded with higher thermal conductivity materials can vary depending upon the cooling requirement.

Figure 3: Details of the cross section AA in Fig. 2 The width of the vent is smaller than the width of rotor 2 to prevent rubbing of pads with the rotor surface. A step 6 is provided in the insert for structural stability.

Figure 1 shows the prior art of the disc brake cooling system. Vents 3 are provided in the region of higher temperature (rotor 2 and pad 1 rubbing zone) to dissipate heat from rotor 2. The vent surface area and the rotor 2 are made of the same materials.

Figure 2 shows one aspect of the invention with vents 4 made of higher thermal conductivity materials (HCM). The location of the new vents 4 is in the same zone as in the prior art, The shape, size and number can vary to suit the cooling requirements. Further, the prior art vents 3 can be totally replaced by the HCM depending upon cooling requirements. Heat generated due to friction between pad 1 and rotor 2 is quickly conducted to the HCM raising its surface temperature. Ambient air sees higher surface temperature and hence, increases the heat transfer from the surface.

Figure 3 shows the cross section AA marked in figure 2. Width of HCM 5 is made less than the width of rotor 2. This ensures that during the braking application, the pad 1 does not directly rub the HCM 5 and thus reduces the stresses induced due to pads. A step 6 is provided in the HCM 5 so that it firmly grips the rotor 2 and provides structural stability during operation.

During hardening process for getting desirable hardness in the disc, the hole provided in the rotor 2 also gets expanded due to the temperature rise. During such stage graphite inserts 5 that have been manufactured with the dimensions (obtained from thermally expanded value) will be inserted in to disc. During cooling phase contraction will force the excess material to go into the groove of the graphite inserts 5 gradually. Eventually when disc reaches the room temperature excess material will be embedded into the groove, thereby preventing the removal of graphite inserts during dynamic condition of vehicle. 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 disc brake system with provision for enhanced cooling comprising a plurality of vents made of high thermal conductivity materials, the heat generated due to braking friction between pad and rotor being quickly conducted to the said materials raising its surface temperature, the ambient air increasing the heat transfer from the surface; the width of the said material being less than the width of the rotor such that the pad does not directly rub against the said material; a step provided in the said material to firmly grip the said rotor for providing structural stability during braking operation; a plurality of graphite inserts irremovably introduced into the disc.

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