12-08-2011, 02:48 PM
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Anti Lock Braking System (ABS)
Introduction
Wheel lockup during braking causes skidding which in turn cause a loss of traction and vehicle control
This reduces the steering ability to change direction. So the car slides out of control
With ABS system, the driver can brake hard, take the evasive action and still be in control of the vehicle in any road condition at any speed and under any load
Fundamentals of ABS
Anti-lock brake systems prevent brakes from locking during braking
On slippery roadways the wheel approach lock up, ABS brakes at this time takes over
ABS brakes modulates brake line pressure and, hence, braking force
Car with and without ABS
Tire Characteristics
Friction-Slip Curve
ABS Design Concept
Retention of vehicle stability and steering ability
Minimum reaction into steering wheel
ABS must utilize available tire-road friction optimally
ABS must adapt quickly to changes in tire-road friction levels.
ABS must minimize the yaw moment
ABS must provide stable braking while turning.
ABS is not a substitute for poor brake balance
ABS malfunctioning must be communicated with the driver
Abs Control Concept
The control of the different brake systems can be accomplished in following three manners:
Single-wheel control
Select-low control
Select-high control
Schematic Diagram of ABS
Types of ABS
Vacuum-powered systems
Separate ABS systems
Integrated ABS systems
Vacuum-powered ABS systems
Vacuum powered ABS systems are not used in the modern vehicles
In 1983, Chrysler and Mitsubishi used vacuum as the power source
It consists of a pressure control section, a vacuum powered pressure drive unit, and solenoid valve
Separate ABS systems
Since the reintroduction of ABS systems between the late ‘70s and mid-‘80s both separate and integrated systems have been used.
In 1978 the separate ABS 2S design manufactured by Bosch and was the first anti-lock brake system to go into mass production with Mercedes Benz automobiles
Contd..
Integrated ABS system
Teves, in 1985 was the first company to introduce a compact integrated ABS system
ABS System Components
Wheel speed sensors
Electronic Control Unit (ECU)
Hydraulic modulator
Electric circuit
Wheel Speed Sensor
The wheel speed sensors signal the wheel speed to the ECU
ECU and Hydraulic Modulator
The ECU receives, amplifies and filters sensors signals, as well as measures and differentiates speeds
The hydraulic modulator converts the ECU commands for pressure modulation in the wheel brakes by use of solenoid valves
In-Use Factors and Operation of ABS Systems
Brake Fluid
Tire Size
Brake Fluid Level
Anti Lock Braking System (ABS)
Introduction
Wheel lockup during braking causes skidding which in turn cause a loss of traction and vehicle control
This reduces the steering ability to change direction. So the car slides out of control
With ABS system, the driver can brake hard, take the evasive action and still be in control of the vehicle in any road condition at any speed and under any load
Fundamentals of ABS
Anti-lock brake systems prevent brakes from locking during braking
On slippery roadways the wheel approach lock up, ABS brakes at this time takes over
ABS brakes modulates brake line pressure and, hence, braking force
Car with and without ABS
Tire Characteristics
Friction-Slip Curve
ABS Design Concept
Retention of vehicle stability and steering ability
Minimum reaction into steering wheel
ABS must utilize available tire-road friction optimally
ABS must adapt quickly to changes in tire-road friction levels.
ABS must minimize the yaw moment
ABS must provide stable braking while turning.
ABS is not a substitute for poor brake balance
ABS malfunctioning must be communicated with the driver
Abs Control Concept
The control of the different brake systems can be accomplished in following three manners:
Single-wheel control
Select-low control
Select-high control
Schematic Diagram of ABS
Types of ABS
Vacuum-powered systems
Separate ABS systems
Integrated ABS systems
Vacuum-powered ABS systems
Vacuum powered ABS systems are not used in the modern vehicles
In 1983, Chrysler and Mitsubishi used vacuum as the power source
It consists of a pressure control section, a vacuum powered pressure drive unit, and solenoid valve
Separate ABS systems
Since the reintroduction of ABS systems between the late ‘70s and mid-‘80s both separate and integrated systems have been used.
In 1978 the separate ABS 2S design manufactured by Bosch and was the first anti-lock brake system to go into mass production with Mercedes Benz automobiles
Contd..
Integrated ABS system
Teves, in 1985 was the first company to introduce a compact integrated ABS system
ABS System Components
Wheel speed sensors
Electronic Control Unit (ECU)
Hydraulic modulator
Electric circuit
Wheel Speed Sensor
The wheel speed sensors signal the wheel speed to the ECU
ECU and Hydraulic Modulator
The ECU receives, amplifies and filters sensors signals, as well as measures and differentiates speeds
The hydraulic modulator converts the ECU commands for pressure modulation in the wheel brakes by use of solenoid valves
In-Use Factors and Operation of ABS Systems
Brake Fluid
Tire Size
Brake Fluid Level
