Fundamentals of Automotive and Engine Technology

——Car brake systems

Braking systems are indispensable for the roadworthiness and safe operation of a motor vehicle in road traffic conditions. They are therefore subject to strict legal requirements. The increasing effectiveness and sophistication demanded of braking systems over the course of time has meant that the mechanical systems have been continually improved. With the advent of microelectronics, the braking system has become a complex electronic system.

Overview

Car braking systems must perform the following fundamental tasks:

Reduce the speed of the vehicle

Bring the vehicle to a halt

Prevent unwanted acceleration during downhill driving

Keep the vehicle stationary when it is stopped

The first three of those tasks are performed by the service brakes. The driver controls the service brakes by operating the brake pedal. The parking brake (“hand brake”) keeps the vehicle stationary once it is at a standstill.

Conventional braking systems

On conventional braking systems, the braking sequence is initiated exclusively by means of force applied to the brake pedal. In the braking systemrsquo;s master cylinder, that force is converted into hydraulic pressure. Brake fluid acts as the transmission medium between the master cylinder and the brakes (Figure 1).

On power-assisted braking systems such as are most frequently used on cars and light commercial vehicles, the actuation pressure is amplified by a brake servo unit (brake booster).

Electronic braking systems

Antilock braking system (ABS)

An electronic braking system was first used on a volume-production vehicle in 1978. ABS (Antilock Braking System) prevents the wheels locking up and the vehicle becoming uncontrollable under heavy braking.

As with conventional systems, an ABS system has a mechanical link between the brake pedal and the brakes. But it also incorporates an additional component, the hydraulic modulator. Solenoid valves in the hydraulic modulator are controlled in such a way that if the degree of wheel slip exceeds a certain amount, the brake pressure in the individual wheel cylinders is selectively limited to prevent the wheels locking.
ABS has been continually improved and developed to the extent that it is now standard equipment on virtually all new vehicles sold in western Europe.

Electrohydraulic brakes (SBC)

SBC (Sensotronic Brake Control) represents a new generation of braking systems. Under normal operating conditions, it has no mechanical link between the brake pedal and the wheel cylinders. The SBC electrohydraulic system detects the brake pedal travel electronically using duplicated sensor systems and analyses the sensor signals in an ECU. This method of operation is sometimes referred to as “brake by wire”. The hydraulic modulator controls the pressure in the individual brakes by means of solenoid valves. Operation of the brakes is still effected hydraulically using brake fluid as the transmission medium.

Electromechanical brakes (EMB)

In the future there will be another electronic braking system, EMB (Electromechanical Brakes), which will operate electromechanically rather than employing hydraulics. Electric motors will force the brake pads against the discs in order to provide the braking action. The link between the brake pedal and the brakes will be purely electronic.

Electronic vehicle-dynamics systems

Continuing development of the ABS system led to the creation of TCS (Traction Control System). This system, which was first seen on volume-production cars in 1987, prevents wheel spin under acceleration and thus improves vehicle handling. Consequently, it is not a braking system in the strict sense of the word. Nevertheless, it makes use of and actively operates the braking system to prevent a wheel from spinning.
Another vehicle-dynamics system is the ESP (Electronic Stability Program), which prevents the vehicle entering a skid within physically determined parameters. It too makes use of and actively controls the braking system in order to stabilise the vehicle.

Ancillary functions of electronic systems

Electronic processing of data also makes possible a number of ancillary functions that can be integrated in the overall electronic braking and vehicle-dynamics systems.

Brake Assistant (BA) increases brake pressure if the driver is hesitant in applying the full force of the brakes in an emergency.

Electronic Braking-force distribution controls the braking force at the rear wheels so that the best possible balance between front and rear wheel braking is achieved.

Hill Descent Control (HDC) automatically brakes the vehicle on steep descents.

History of the brake

Origin and development

The first use of the wheel is dated to 5,000 B.C. Usually, cattle were used as draft animals; later, horses and donkeys were also used. The invention of the wheel made it necessary to invent the brake. After all, a horse-drawn carriage traveling downhill had to be slowed down, not only to keep its speed within controllable limits, but also to prevent it running into the back of the horses. This was likely done using wooden rods braced against the ground or the wheel disks. Beginning around 700 B.C., wheels acquired iron tires to prevent premature wear of the wheel rim.

Beginning in 1690, coach drivers used a “chock” to brake their carriages. While driving downhill, they used its handle push it under a wheel, which then was immobilized and slid onto the chock.
In 1817, at the dawn of the industrial age, Baron Karl Drais rode from Karlsruhe in southern Germany to Kehl, proving to a stunned public that it is possible to ride on two wheels without falling over.

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Fundamentals of Automotive and Engine Technology

——Car brake systems

Braking systems are indispensable for the roadworthiness and safe operation of a motor vehicle in road traffic conditions. They are therefore subject to strict legal requirements. The increasing effectiveness and sophistication demanded of braking systems over the course of time has meant that the mechanical systems have been continually improved. With the advent of microelectronics, the braking system has become a complex electronic system.

Overview

Car braking systems must perform the following fundamental tasks:

Reduce the speed of the vehicle

Bring the vehicle to a halt

Prevent unwanted acceleration during downhill driving

Keep the vehicle stationary when it is stopped

The first three of those tasks are performed by the service brakes. The driver controls the service brakes by operating the brake pedal. The parking brake (“hand brake”) keeps the vehicle stationary once it is at a standstill.

Conventional braking systems

On conventional braking systems, the braking sequence is initiated exclusively by means of force applied to the brake pedal. In the braking systemrsquo;s master cylinder, that force is converted into hydraulic pressure. Brake fluid acts as the transmission medium between the master cylinder and the brakes (Figure 1).

On power-assisted braking systems such as are most frequently used on cars and light commercial vehicles, the actuation pressure is amplified by a brake servo unit (brake booster).

Electronic braking systems

Antilock braking system (ABS)

An electronic braking system was first used on a volume-production vehicle in 1978. ABS (Antilock Braking System) prevents the wheels locking up and the vehicle becoming uncontrollable under heavy braking.

As with conventional systems, an ABS system has a mechanical link between the brake pedal and the brakes. But it also incorporates an additional component, the hydraulic modulator. Solenoid valves in the hydraulic modulator are controlled in such a way that if the degree of wheel slip exceeds a certain amount, the brake pressure in the individual wheel cylinders is selectively limited to prevent the wheels locking.
ABS has been continually improved and developed to the extent that it is now standard equipment on virtually all new vehicles sold in western Europe.

Electrohydraulic brakes (SBC)

SBC (Sensotronic Brake Control) represents a new generation of braking systems. Under normal operating conditions, it has no mechanical link between the brake pedal and the wheel cylinders. The SBC electrohydraulic system detects the brake pedal travel electronically using duplicated sensor systems and analyses the sensor signals in an ECU. This method of operation is sometimes referred to as “brake by wire”. The hydraulic modulator controls the pressure in the individual brakes by means of solenoid valves. Operation of the brakes is still effected hydraulically using brake fluid as the transmission medium.

Electromechanical brakes (EMB)

In the future there will be another electronic braking system, EMB (Electromechanical Brakes), which will operate electromechanically rather than employing hydraulics. Electric motors will force the brake pads against the discs in order to provide the braking action. The link between the brake pedal and the brakes will be purely electronic.

Electronic vehicle-dynamics systems

Continuing development of the ABS system led to the creation of TCS (Traction Control System). This system, which was first seen on volume-production cars in 1987, prevents wheel spin under acceleration and thus improves vehicle handling. Consequently, it is not a braking system in the strict sense of the word. Nevertheless, it makes use of and actively operates the braking system to prevent a wheel from spinning.
Another vehicle-dynamics system is the ESP (Electronic Stability Program), which prevents the vehicle entering a skid within physically determined parameters. It too makes use of and actively controls the braking system in order to stabilise the vehicle.

Ancillary functions of electronic systems

Electronic processing of data also makes possible a number of ancillary functions that can be integrated in the overall electronic braking and vehicle-dynamics systems.

Brake Assistant (BA) increases brake pressure if the driver is hesitant in applying the full force of the brakes in an emergency.

Electronic Braking-force distribution controls the braking force at the rear wheels so that the best possible balance between front and rear wheel braking is achieved.

Hill Descent Control (HDC) automatically brakes the vehicle on steep descents.

History of the brake

Origin and development

The first use of the wheel is dated to 5,000 B.C. Usually, cattle were used as draft animals; later, horses and donkeys were also used. The invention of the wheel made it necessary to invent the brake. After all, a horse-drawn carriage traveling downhill had to be slowed down, not only to keep its speed within controllable limits, but also to prevent it running into the back of the horses. This was likely done using wooden rods braced against the ground or the wheel disks. Beginning around 700 B.C., wheels acquired iron tires to prevent premature wear of the wheel rim.

Beginning in 1690, coach drivers used a “chock” to brake their carriages. While driving downhill, they used its handle push it under a wheel, which then was immobilized and slid onto the chock.
In 1817, at the dawn of the industrial age, Baron Karl Drais rode from Karlsruhe in southern Germany to Kehl, proving to a stunned public that it is possible to ride on two wheels without falling over.

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