DIFFERENT TYPES OF REGENERATIVE BRAKING SYSTEM

Based on the mode of storage of energy some of the system developed can be listed they are:-

TYPES OF REGENERATIVE BRAKING SYSTEM:

Electric Regenerative braking system
Hydraulic Regenerative Brakes
Fly Wheels etc.

Electric Regenerative braking system:

In an electric system which is driven only by means of electric motor the system

consists of an electric motor which acts both as generator and motor. Initially when the system is cruising the power is supplied by the motor and when the there is a necessity for braking depending upon driver’s applied force on the brake pedal the electronic unit controls the charge flowing through the motor and due to the resistance offered motor rotates back to act as a generator and the energy is energy is stored in a battery or bank of twin layer capacitors for later use.

In hybrid system motor will be coupled to another power source normally I.C Engines.

The main components of this system

Engine
Motor/Generator
Batteries
Electronic control system

Hydraulic Regenerative Brakes

Hydrostatic Regenerative Braking (HRB) system uses electrical/electronic Components as well as hydraulics to improve vehicle fuel economy. An alternative regenerative braking system is being developed by the Ford Motor Company and the Eaton Corporation. It's called Hydraulic Power Assist or HPA. With HPA, when the driver steps on the brake, the vehicle's kinetic energy is used to power a reversible pump, which sends hydraulic fluid from a low pressure accumulator (a kind of storage tank) inside the vehicle into a high pressure accumulator. The pressure is created by nitrogen gas in the accumulator, which is compressed as the fluid is pumped into the space the gas formerly occupied. This slows the vehicle and helps bring it to a stop. The fluid remains under pressure in the accumulator until the driver pushes the accelerator again, at which point the pump is reversed and the pressurized fluid is used to accelerate the vehicle, effectively translating the kinetic energy that the car had before braking into the mechanical energy that helps get the vehicle back up to speed. It's predicted that a system like this could store 80 percent of the momentum lost by a vehicle during deceleration and use it to get the vehicle moving again.

The Hydrostatic Regenerative Braking (HRB) system is intended for commercial vehicles and mobile equipment. The company says that initial measurements show that the HRB system reduces the fuel consumption in these vehicles by up to 25%.

In the HRB system, braking energy is converted to hydraulic pressure and stored in a high-pressure hydraulic accumulator. When the vehicle accelerates, the stored hydraulic energy is applied to the transmission reducing the energy that the combustion engine has to provide. An electronic controller and a hydraulic valve manifold control the process.

At present, these hydraulic regenerative brakes are noisy and prone to leaks; however, once all of the details are ironed out, such systems will probably be most useful in large trucks.

Fly Wheels

Regenerative brakes may seem very hi-tech, but the idea of having "energy-saving Reservoirs" in machines is nothing new. Engines have been using energy-storing devices called flywheels virtually since they were invented.

The basic idea is that the rotating part of the engine incorporates a wheel with a very heavy metal rim, and this drives whatever machine or device the engine is connected to. It takes much more time to get a flywheel-engine turning but, once it's up to speed, the flywheel stores a huge amount of rotational energy. A heavy spinning flywheel is a bit like a truck going at speed: it has huge momentum so it takes a great deal of stopping and changing its speed takes a lot of effort. That may sound like a drawback, but it's actually very useful. If an engine supplies power erratically, the flywheel compensates, absorbing extra power and making up for temporary lulls, so the machine or equipment it's connected to is driven more smoothly.

It's easy to see how a flywheel could be used for regenerative braking. In something like a bus or a truck, you could have a heavy flywheel that could be engaged or disengaged from the transmission at different times. You could engage the flywheel every time you want to brake so it soaked up some of your kinetic energy and brought you to a halt. Next time you started off, you'd use the flywheel to return the energy and get you moving again, before disengaging it during normal driving. The main drawback of using flywheels in moving vehicles is, of course, their extra weight. They save you energy by storing power you'd otherwise squander in brakes, but they also cost you energy because you have to carry them around all the time.

The transfer of energy in both directions (captured from the driveline during coasting and braking, and released to the driveline for boost) is managed through a CVT (Continuously Variable Transmission) gear box. Packaged inside a single housing is a shaft mounted flywheel that is connected via a chain/gear or belt/pulley drive to a series of discs and rollers (the CVT). During braking and coasting, the flywheel spools-up (accelerates as it spins) and absorbs a storehouse of otherwise wasted energy (heat from friction brakes). During power delivery, as the vehicle begins to accelerate, the pent-up energy in the flywheel is released and it turns the shaft. The rollers within the CVT can change position across the discs and either retard or augment the torque of the spinning flywheel shaft much like a conventional step-up or step-down gear box. This “gearing” is necessary, because unlike aircraft, and to a certain extent watercraft, which travel at a relatively constant load and speed, earth-bound vehicles travel at regularly and greatly varying speeds and loads as they negotiate traffic and topography. It is this variable output velocity that allows for smooth power transmission from the flywheel to the driveline as the vehicle travels over the roadway.

Advanced transmissions that incorporate hi-tech flywheels are now being used as regenerative systems in such things as formula-1 cars, where they're typically referred to as Kinetic Energy Recovery Systems (KERS).

CHECK OUT: REGENERATIVE BRAKING SYSTEM PROJECT REPORT

Wikipedia

Question 2

Why Regenerative Brakes are assisted with the Frictional Brake?

mechanical-farm · Accepted Answer

The friction brake is a necessary back-up in the event of failure of the regenerative brake.

Most road vehicles with regenerative braking only have power on some wheels (as in a two-wheel drive car) and regenerative braking power only applies to such wheels, so in order to provide controlled braking under difficult conditions (such as in wet roads) friction based braking is necessary on the other wheels.

The amount of electrical energy capable of dissipation is limited by either the capacity of the supply system to absorb this energy or on the state of charge of the battery or capacitors. No regenerative braking effect can occur if another electrical component on the same supply system is not currently drawing power and if the battery or capacitors are already charged. For this reason, it is normal to also incorporate dynamic braking to absorb the excess energy.

Under emergency braking it is desirable that the braking force exerted be the maximum allowed by the friction between the wheels and the surface without slipping, over the entire speed range from the vehicle's maximum speed down to zero. The maximum force available for acceleration is typically much less than this except in the case of extreme high-performance vehicles. Therefore, the power required to be dissipated by the braking system under emergency braking conditions may be many times the maximum power which is delivered under acceleration. Traction motors sized to handle the drive power may not be able to cope with the extra load and the battery may not be able to accept charge at a sufficiently high rate. Friction braking is required to absorb the surplus energy in order to allow an acceptable emergency braking performance.

For these reasons there is typically the need to control the regenerative braking and match the friction and regenerative braking to produce the desired total braking output.

CHECK OUT: REGENERATIVE BRAKING SYSTEM PROJECT REPORT

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