Types of Drum Brakes

The different types of Drum Brake Systems are enumerated below:

Mechanical Drum Brake

The mechanical drum brake system encompasses applications in two-wheelers and auto rickshaws. Within this setup, a cam is affixed to the brake linkage and pedal, serving as the actuator for the brake shoes. Upon pressing the brake pedal, the cam initiates a rotational motion, prompting the brake shoes to expand outward and make contact with the drum. 

This contact generates friction between the brake linings and the drum, resulting in the cessation of drum rotation and subsequently stopping the wheel's movement. Upon releasing the brake pedal, retracting springs restore the brake shoes to their original position, creating a gap between them and the drum allowing free rotation once again.

Hydraulic Drum Brake

A step ahead of the mechanical system is the hydraulic drum brake, commonly found in cars. In this design, the cam is replaced by a hydraulic wheel cylinder. Within this hydraulic setup, the pistons of the wheel cylinder exert force to push the brake shoes outward. The brake shoes are positioned on the anchor plate or braking plate, which consolidates the various components of the brake system and secures them to the vehicle's axle. Pressing the brake pedal prompts the hydraulic force multiplication in the brake master cylinder, amplifying the pressure transmitted to the wheel cylinders. This, in turn, urges the pistons to push the brake shoes outward, generating friction between the linings and the drum. The resulting friction halts the drum's rotation, leading to the cessation of the wheel's movement.

Pneumatic-Assisted Drum Brake:

The third variant, the pneumatic-assisted drum brake system, is actuated by air pressure and follows the principles of the mechanical drum brake system. It relies on a larger cam or an 'S-shaped cam, commonly referred to as the "S-Cam" brake system. However, the distinctive feature here is the utilization of high-pressure compressed air to activate a pneumatic piston, setting the cam into motion. 

This configuration is predominantly employed in medium to heavy commercial vehicles, where the pneumatic piston's action on the cam initiates the braking process. The friction between the brake linings and the drum, caused by the outward expansion of the brake shoes, leads to the halt of drum rotation and subsequent wheel immobilization.

Brake Drum

Types of Drum Brakes Based on the Principle

The various types of Drum Brakes are discussed below:

Leading/Trailing Shoe Type Drum Brake:

• In the Drum brake mechanisms, the "leading shoe" and the "trailing shoe" have an important role to play. The term "leading shoe" denotes the shoe that moves in the same direction as the drum's rotation when pressed against it. Conversely, the other shoe is referred to as the "trailing shoe." 
• The application of pressure on the leading shoe aligns with the drum's rotational direction, harnessing the drum's rotation to enhance the pressure on the shoes and consequently elevate the braking force. This phenomenon is known as the servo effect or self-boosting effect, which contributes to the potent braking capabilities of drum brakes.
• Structurally, a wheel cylinder encases a piston responsible for generating hydraulic pressure that urges the two shoes against the inner surface of the drum.
• These shoes exhibit adaptability, transforming into either the leading or trailing shoe depending on the vehicle's forward or backward motion. Regardless of the vehicle's direction, drum brakes consistently generate equivalent braking force. This design is predominantly employed for the rear brakes in passenger cars.

Twin Leading Shoe Type Drum Brake:

• The twin leading shoe drum brake configuration entails the presence of two-wheel cylinders and two leading shoes. Each wheel cylinder exerts pressure on a shoe, enabling both shoes to function as leading shoes when the vehicle moves forward, resulting in heightened braking effectiveness.
• The pistons housed within the wheel cylinders exhibit unidirectional displacement, causing both shoes to function as trailing shoes when the vehicle is in reverse. This type is commonly adopted for the front brakes of small-to-mid-sized trucks.
• In the dual twin leading shoe variant, pistons displace in both directions, allowing both shoes to act as leading ones, irrespective of the vehicle's travel direction. This arrangement is mainly employed for the rear brakes in small-to-mid-sized trucks.

Duo-Servo Type Drum Brake:

• The duo-servo drum brake design introduces a configuration where two brake shoes, designated as the primary shoe and the secondary shoe, are interlinked through an adjuster. The formidable pressure arising from the primary shoe's servo effect gets transmitted to the linked secondary shoe, generating a substantial braking force.
• This particular type finds its primary application as parking brakes in passenger cars, center brakes in trucks, and brakes in forklifts.

Brake Drum material

The Brake drum material can be Aluminium, Cast Iron, or Steel. An elaboration of the same is given below:

Aluminium:

• Aluminium brake drums are significantly lighter compared to cast iron, which can contribute to reduced overall vehicle weight.
• Aluminum's high thermal conductivity allows for better heat dissipation, reducing the risk of brake fade and maintaining consistent braking performance.
• Aluminium has natural corrosion resistance, making it suitable for environments with high humidity or road salt exposure.
• While aluminium drums offer good heat management, their cost can be higher due to the more intricate manufacturing process and material expense.
• Aluminium brake drums are commonly found in lightweight vehicles or certain high-performance applications.

Cast Iron:

• Cast iron is known for its durability and ability to withstand high levels of heat and friction generated during braking.
• Cast iron brake drums are commonly used across a wide range of vehicles, from passenger cars to heavy-duty trucks, due to their robust nature.
• Cast iron has a relatively high heat capacity, allowing it to absorb and dissipate heat effectively, reducing the risk of brake fade.
• Cast iron is generally more cost-effective to produce compared to aluminium, making it a practical choice for mass-produced vehicles.
• Cast iron is heavier than aluminium, which might slightly impact overall vehicle weight and fuel efficiency.

Steel Brake:

• Steel brake drums are often used in heavy-duty and commercial vehicles due to their strength and ability to handle substantial loads.
• Steel's toughness and resistance to wear make it suitable for vehicles subjected to harsh operating conditions and frequent heavy braking.
• While steel is not as effective at heat dissipation as aluminium or cast iron, it still maintains reasonable heat management capabilities.
• Steel drums can be manufactured in various shapes and sizes to accommodate the specific braking requirements of different vehicles.
• Steel brake drums are heavier than both aluminium and cast iron, potentially affecting fuel efficiency in smaller vehicles.

Drum Brakes vs Disc Brakes

The difference between drum brakes and disc brakes is discussed below.

Advantage of Drum Brakes

The various advantages include:

• Drum brakes have simplicity in design and components
• It has cost-effective manufacturing
• The maintenance demands for drum brakes are minimal
• These brakes have extended longevity
• Smooth braking engagement
• Drum brakes have a consistent performance
• These brakes have compartmentalised protection
• Drum brakes can be integrated into older vehicle models
• Compared to disc brakes, drum brakes are less susceptible to contamination from brake fluid leaks due to their internal design.

Disadvantages of Drum Brakes

Some of the noteworthy disadvantages are:

• Drum brakes don't stop as quickly as disc brakes.
• They can become less effective after being used for a while.
• The brake lining in some drum brakes contains harmful asbestos fibres.
• Drum brakes might not work well in wet conditions.
• Without asbestos linings, they can suddenly grab due to moisture.