Describe the difference between a dual-servo and a leading–trailing drum brake system.
The correct answer and explanation is :
A dual-servo brake system and a leading-trailing drum brake system are both types of drum brake systems, but they operate differently and have distinct designs to achieve braking efficiency.
Dual-Servo Brake System:
In a dual-servo brake system, the brake shoes are positioned inside the drum, and there are two sets of shoes: a leading shoe and a trailing shoe. The system uses a self-energizing mechanism where the rotation of the drum helps apply force to the shoes, enhancing braking efficiency. In this design, when the brakes are applied, the leading shoe presses against the drum, causing the rotation to help pull the trailing shoe into contact with the drum as well. This results in both shoes being involved in braking, hence the term “dual-servo.”
The key feature of a dual-servo system is that it provides more braking force due to the dual action, where both shoes work together to maximize braking power. This system is more effective at higher speeds, as the force is distributed between the shoes, reducing wear and improving braking stability.
Leading-Trailing Drum Brake System:
In a leading-trailing drum brake system, there are two brake shoes as well, but only one shoe is self-energizing. The design of the system relies on the arrangement where one shoe is a leading shoe and the other is a trailing shoe. The leading shoe faces the rotation of the drum and receives more force during braking, while the trailing shoe follows the rotation.
This system is less efficient than the dual-servo design because it relies on a single leading shoe for the majority of the braking force. The trailing shoe doesn’t benefit from self-energizing forces, which means the braking power is limited and more effort is needed to stop the vehicle.
Comparison and Explanation:
- Efficiency: The dual-servo system is more efficient because both shoes contribute to braking, increasing overall braking power. The leading-trailing system relies more on the leading shoe and is less efficient in comparison.
- Design: Dual-servo systems are typically used in heavier vehicles due to their enhanced braking capabilities. Leading-trailing systems are simpler and are more commonly found in smaller vehicles or as an older design.
- Braking Force: Dual-servo provides more effective stopping power at higher speeds due to the increased friction from both shoes. In contrast, the leading-trailing system is less powerful under similar conditions.
In summary, while both systems are used for braking in drum brakes, the dual-servo system is superior in terms of efficiency and braking performance, especially for heavier loads and high-speed scenarios. The leading-trailing system, though simpler, is less effective in comparison.