Types of brake systems: the principle of operation of drum and disc brakes
Content
The brake system is designed to control the speed of the car, stop it, and hold it in place for a long time by using the braking force between the wheel and the road. Braking force can be generated by a wheel brake, a vehicle engine (called engine braking), a hydraulic or electric retarder in the transmission.
To implement these functions, the following types of brake systems are installed on the car:
- Working brake system. Provides controlled deceleration and vehicle stopping.
- Spare brake system. Used in case of failure and malfunction of the working system. It performs similar functions as the working system. A spare brake system can be implemented as a special autonomous system or as part of a working brake system (one of the brake drive circuits).
- Parking brake system. Designed to hold the car in place for a long time.
The braking system is the most important means of ensuring the active safety of the car. On cars and a number of trucks, various devices and systems are used to increase the efficiency of the braking system and braking stability.
How the brake system works
When you press the brake pedal, the load is transferred to the amplifier, which creates additional force on the main brake cylinder. The brake master cylinder piston pumps fluid through pipes to the wheel cylinders. This increases the fluid pressure in the brake actuator. The pistons of the wheel cylinders move the brake pads to the discs (drums).
Further pressure on the pedal increases the fluid pressure and the brakes are activated, which slows the rotation of the wheels and the appearance of braking forces at the point of contact of the tires with the road. The more force is applied to the brake pedal, the faster and more efficiently the wheels are braked. The fluid pressure during braking can reach 10-15 MPa.
At the end of braking (releasing the brake pedal), the pedal under the influence of a return spring moves to its original position. The piston of the main brake cylinder moves to its original position. Spring elements move the pads away from the discs (drums). The brake fluid from the wheel cylinders is forced through pipelines into the master brake cylinder. The pressure in the system drops.
Types of brake systems
The brake system combines the brake mechanism and the brake drive. The brake mechanism is designed to create the braking torque necessary to slow down and stop the car. Friction brake mechanisms are installed on cars, the operation of which is based on the use of friction forces. The brake mechanisms of the working system are installed directly in the wheel. The parking brake may be located behind the gearbox or transfer case.
Depending on the design of the friction part, there are drum and disk braking mechanisms.
The brake mechanism consists of a rotating and a fixed part. As a rotating part drum mechanism a brake drum is used, a fixed part - brake pads or bands.
rotating part disk mechanism represented by a brake disc, fixed - by brake pads. On the front and rear axles of modern passenger cars, as a rule, disc brakes are installed.
How drum brakes work
The main internal parts of drum brakes are:
- Brake drum. An element made of high-strength cast iron alloys. It is mounted on a hub or a support shaft and serves not only as the main contact part that interacts directly with the pads, but also as a housing in which all other parts are mounted. The inner part of the brake drum is ground for maximum braking efficiency.
- Pads. Unlike disc brake pads, drum brake pads are semi-circular in shape. Their outer part has a special asbestos coating. If brake pads are installed on a pair of rear wheels, then one of them is also connected to the parking brake lever.
- Tension springs. These elements are attached to the upper and lower parts of the pads, preventing them from moving in different directions at idle.
- Brake cylinders. This is a special body made of cast iron, on both sides of which working pistons are mounted. They are activated by hydraulic pressure that occurs when the driver presses the brake pedal. Additional parts of the pistons are rubber seals and a valve to remove air trapped in the circuit.
- Protective disk. The part is a hub-mounted element to which brake cylinders and pads are attached. Their fastening is carried out by using special clamps.
- Self-advance mechanism. The basis of the mechanism is a special wedge, deepening as the brake pads are worn down. Its purpose is to ensure constant pressing of the pads to the surface of the drum, regardless of the wear of their working surfaces.
**The components listed by us are generally accepted. They are used by most major manufacturers. There are a number of parts that are privately installed by some companies. Such, for example, are the mechanism for bringing the pads, all kinds of spacers, etc.
Principle of operation: the driver, if necessary, presses the pedal, creating increased pressure in the brake circuit. The hydraulics press on the master cylinder pistons, which actuate the brake pads. They "diverge" to the sides, stretching the coupling springs, and reach the points of interaction with the working surface of the drum. Due to the friction that occurs in this case, the speed of rotation of the wheels decreases, and the car slows down. The general algorithm for the operation of drum brakes looks exactly like this. There are no significant differences between systems with one piston and two.
Advantages and Disadvantages of Drum Brakes
Among advantages The drum system can be distinguished by the simplicity of design, a large area of contact between the pads and the drum, low cost, relatively low heat generation, and the possibility of using inexpensive brake fluid with a low boiling point. Also, among the positive aspects is a closed design that protects the mechanism from water and dirt.
Disadvantages of drum brakes:
- slow response;
- performance instability;
- poor ventilation;
- the system works to break, which limits the permissible pressure force of the pads on the drum walls;
- with frequent braking and high loads, deformation of the drum due to strong heating is possible.
In modern cars, drum brakes are used less and less. Basically they are put on the rear wheels in budget models. In this case, they are also used to implement parking brakes.
At the same time, by increasing the size of the drum, it is possible to achieve an increase in the power of the brake system. This led to the widespread use of drum brakes in trucks and buses.
How disc brakes work
The disc brake mechanism consists of a rotating brake disc, two fixed pads mounted inside the caliper on both sides.
In this system, the pads mounted on the caliper are pressed on both sides to the planes of the brake disc, which is bolted to the wheel hub and rotates with it. Metal brake pads have friction linings.
The caliper is a body made of cast iron or aluminum in the form of a bracket. Inside it is a brake cylinder with a piston that presses the pads against the disc during braking.
The bracket (caliper) can be floating or fixed. The floating bracket can move along the guides. She has one piston. The fixed design caliper has two pistons, one on each side of the disc. Such a mechanism is able to press the pads against the brake disc more strongly and is used mainly in powerful models.
Brake discs are made from cast iron, steel, carbon and ceramic. Cast iron discs are inexpensive, have good frictional qualities and a fairly high wear resistance. Therefore, they are most often used.
Stainless steel tolerates temperature changes better, but its frictional properties are worse.
Lightweight carbon discs have a high coefficient of friction and excellent heat resistance. But they require preheating, and their cost is too high. The scope of carbon brake discs is sports cars.
Ceramics is inferior to carbon fiber in terms of friction coefficient, but it works well at high temperatures, has significant strength and wear resistance at low weight. The main disadvantage of such discs is the high cost.
Advantages and disadvantages of disc brakes
The advantages of disc brakes:
- less weight compared to the drum system;
- ease of diagnosis and maintenance;
- better cooling due to open design;
- stable operation in a wide temperature range.
Disadvantages of disc brakes:
- significant heat dissipation;
- the need for additional amplifiers due to the limited area of \uXNUMXb\uXNUMXbcontact between the pads and the disk;
- relatively fast pad wear;
- the cost is higher than that of the drum system.
