Essential Components of Vehicle Braking Systems

Variable Brake Limiters for Cargo Vehicles

For certain types of cargo vehicles, the effectiveness of rear axle braking is a dominant factor. These vehicles often bear very little weight when empty, yet carry more than 50% of their total weight when loaded. In such cases, it is essential to use a variable brake limiter capable of adjusting the braking pressure to the rear wheels based on the weight resting on them.

The antagonistic spring force within the limiter varies according to the load. This mechanism, where an antagonistic tension spring applies a cut-off to the valve, adjusts the braking pressure based on the weight supported by the rear axle. For greater loads, higher tension is exerted on the spring, leading to a higher braking pressure applied to the rear wheels. The cut-off pressure to the rear wheels, regulated by a valve cap, restricts the pressure when it exceeds a predetermined limit, ensuring balanced braking performance.

Brake Lines and Hydraulic Fluid Properties

The master cylinder (pump) connects to each wheel cylinder through brake lines, forming the hydraulic circuit. This circuit delivers brake fluid to the wheel cylinders under the pressure generated by the pump. These lines feature a rigid structure in some sections and flexible hoses in others, allowing for relative movement between different components of the braking system.

Brake fluid, a critical component, must meet the following requirements:

• It must have a high boiling point, typically between 230°C and 244°C, to prevent vapor lock under high temperatures.
• Brake fluid is hygroscopic, meaning it can absorb moisture. This property helps prevent water from freezing or boiling within the system, but also necessitates periodic replacement.
• It must possess anti-corrosive properties to prevent chemical interaction and damage to the metallic and rubber components of the brake system.
• Manufacturers generally recommend periodically changing the brake fluid every two years or every 80,000 km, whichever comes first, to maintain optimal performance and safety.

Understanding the Mastervac Brake Booster

When vehicle characteristics permit, a Mastervac brake booster system is installed. In this system, the master cylinder is integrated directly onto the brake booster unit. It consists of its own cylinder, which houses the piston that forms the vacuum chambers, as well as a control valve incorporated into the piston and simultaneously attached to the brake pedal push rod.

This braking assistance is activated or deactivated based on the effort exerted on the brake pedal. The system includes a reaction piston disc with a vacuum hole that can connect the vacuum chambers to each other or to the atmosphere. The master cylinder is securely fixed to the casing of the vacuum chamber and is actuated by a push rod.

A crucial part of the plunger is mounted on a rubber diaphragm, forming two independent chambers. In the rest position, these chambers are interconnected and subject to the engine's vacuum. When the engine runs, the depression (vacuum) in the intake manifold creates a progressive vacuum in the chamber connected to the engine. Since this chamber is in communication, the same vacuum is established on both sides of the piston, preparing the system for brake assistance.