Assistive Braking Technologies
After the introduction to the working and types of brakes in previous blogs now we can talk about the various safety stipulations and methodologies used to make braking safer and energy efficient.
Please go through the following links to ensure complete understanding of the subject
Antilock Brake System (ABS)
It not only helps in stopping in a straight line without losing grip but also works on providing the directional stability. The basic method to avoid wheel lock is Pressure Modulation, where the braking pressure is reduced just before the wheel starts to skid and it is repeated at a rate of 15 times per second.
The locking of front wheels reduces maneuverability while locking of rear brakes causes stability reduction. The feel of ABS-equipped brakes is different from conventional brakes, on an emergency application when you press the pedal firmly, there are some pulsations which may be quite violent but don’t let of the pedal. This system is available for both two-wheel drive and four-wheel drives and is further divided into channels to operate a pair of wheels together or operate them independently.
Construction- It consists of an electric control unit (ECU), a sensor on each wheel to calculate slip rate, a hydraulic pump, and a pressure accumulator to store hydraulic fluid. A lateral acceleration sensor is also used to monitor lateral acceleration and use ABS on turns also.
Manufacturers- Bendix, Bosch, Delco Moraine, Kelsey-Haynes and Lucas Girling.
Emergency Brake Assist
This system detects the extent of emergency from the speed with which the driver lifts the foot from the throttle and stamps the brakes, accordingly, the servo brakes are applied to maximum intensity till the car stops or driver removes his foot from brakes. As the name suggests it is an assistive technology and is employed with ABS. this system was introduced by Mercedes.
Dynamic Braking System
This system monitors the speed and load of each wheel individually and applies brakes accordingly. For the special cases like when the car is taking a right turn and brakes are applied, according to the weight transfer of the vehicle.
It is different from ABS as in DBS the conditions are monitored all the time unlike in ABS where the operation begins only when the wheels are about to skid.
Application- High-end luxury cars.
Brake by Wire
Here no mechanical linkage is present between the brake pedal and wheels.
Construction- It consists of two circuits. The brake pedal is connected to a hypersensitive rheostat which measures the electric signal in the circuit. The force and the displacement of the brake pedal decide how much electrical signal is sent to the brake computer and brakes will be applied by the servo pump with same intensity using the secondary hydraulic circuit. To provide the feel of braking the fluid pressure is measured by sensors and sent back to the brake computer that sends the feedback to the pedal.
- The brake pedal can be placed anywhere as there is no restriction by the hydraulic circuit.
- There will not be any pulsations when the ABS is working.
- It can coordinate with the cruise control system better to cope with the emergency situations.
Regenerative Braking System
It helps to harvest the heat energy generated while braking using the flywheels and batteries. Both regenerative brakes and conventional brakes have the same pedal, as the brakes are applied the electric motors reverse the direction to work as generators. The torque produced by this reversal in direction opposes the forward momentum and stops the car along with generation of electricity.
Application- in Electric vehicles(EV) and Hybrid Electric Vehicles(HEV). They use regenerative braking at lower speeds and conventional brakes at higher speeds, as the regenerative brakes can’t be relied upon to stop the vehicle the can only decrease the speeds.
Flywheel Energy Storages(FES) are the Kinetic Energy Recovery Systems(KERS)
Here the energy is captured in a small flywheel that is made to rotate at very high speeds, up to 80,000 rpm using CVT or by electric motor and generator. Electric FES is more efficient as energy doesn’t change its form throughout the working cycle.
This is the latest technology developed by Mazda where the use of capacitors to store energy.
Electric-Hydraulic Combi Brake
Here the front axle has hydraulically operated brakes and rear axle has electro-mechanical brakes. The system works on a 12 V battery system and there is no hydraulic connection to the rear axle.
- High operational ease and safety.
- Integration of brakes with other vehicle control features.
Sensotronic Brake Control
Here electric pulses are used to transfer the braking commands of the driver onto a microcomputer which processes the various sensor signals simultaneously and depending on the driving situation, calculates the optimum brake pressure for each wheel and applies it. A high-pressure reservoir and electronically controlled valves ensure the availability of the brake pressure and also decrease the time of braking. It is developed by Bosch and Mercedes-Benz.
- Helps to optimize the other safety functions like ABS, ASP etc.
- The soft-stop function that provides a soft and smooth stop.
- Dry brake function provides regular short and weak brake impulses to dry out the water film on brake disc on wet roads and ensuring full and immediate braking effect.
- Drive-away assistant prevents rolling of vehicle backward on a hill, it is activated by pressing the brake pedal quickly and firmly and the effect is canceled next time you press the accelerator pedal.
Siemens VDO Electronic Wedge Brakes(EWB)
It is a brake by wire system working on 12 V supply and is expected to provide improved safety and comfort relative to hydraulic brakes.
EWB has an intelligent wheel braking module on each wheel. The module consists of-
- Brake Disc, which absorbs the kinetic energy.
- Brake caliper on either side.
- Brake pads. Stationary brake pad on one side and moving brake pad on another side of the disc.
‘Electric motor controls the position of the moving pad with wedge mechanism.
- Wedge bearing mechanism provides a connection between the brake caliper and moving brake pad.
The sensor system monitors the movement and force.
Working- When the brake pedal is pressed, the EWB system sends the signal electronically to all the brake modules, the electric motors actuate the wedge bearing mechanism to move the wedge into the required position using the sensor mechanism. It causes the moving brake pad to be pressed against the brake disc. The possibility of wedge blocking is avoided by electronic control.
- Simple construction, weight reduction and greater reliability due to the removal of many components.
- This system not only helps in braking but also used as an automatic parking brake, for this only a parking switch is required which activates all four modules.
- Can be adapted to new vehicles more easily and faster, reducing the development cost.
- No pulsations of brake pedal due to ABS.
Carbon Ceramic Brakes
Their use has been so far limited to racing applications and high-end cars due to their high costs. But this cost is expected to come down with new manufacturing processes.
Construction- The brake disc made up of silicon carbide which is an abrasion resistant crystalline compound with a structure similar to diamond. Fibers of carbon are embedded into the disc to help the silicon carbide absorb and cope with large stresses. These materials help the brakes to achieve the uniform coefficient of friction, which provides consistent pedal feel and braking distances regardless of weather and temperature.
- Weight reduction of the disc, which gives sharper turning.
- Long Life.
- Superior fade resistance.
- They use large calipers to spread the clamping force over a wider area and increasing the life with improved performance.
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