Regenerative braking system

[ajayd]

I am very new to regenrative braking systems and wanted to do some research on.
from Internet waht I could able to grasp was regenerative braking involves the electrical motor which is turned to generator when brakes are applied and so the energy is reclaimed, but how the mechanical system works ? how much time it is needed for motor to sense the brakes are applied and motor to turn into generator ? are the brakes used are normal brakes and used for all the wheels ?

 

[tbuelna]

effective automotive regenerative braking:

http://www.epa.gov/otaq/technology/420f04024.pdf

 

[ajayd]

though the .pdf file is self explanatory and explain a lot about hydrolysic system
is there any resource on internet or any book I can refere to grasp the basic mechanical aspects of regenerative braking system?

 

[rhpope]

I did some chassis design work on a fully electric commercial bus. In this case, the two electric motors that are driving the transmission act as generators as soon as you let off of the accelerator pedal. All of this was controlled with simple electronics that sensed that you let off of the accelerator pedal. The generator effect also worked in place a transmission retarder or exhaust brake as typically used in the diesel bus applications. Hope this helps a little at least on fully electric vehicles.

 

[EdDanzer]

Regenerative braking is a method to capture and store the kinetic energy of a moving item, and then be used to reaccelerate it. Regenerative braking is not industry specific, but can be difficult to implement cost effectively. In most application a heavy load must be stopped and started frequently. The action of starting and stopping is controlled to limit power required.

In industrial applications, the acceleration time and the deceleration time is usually easy to determine and microprocessor controlled.
In an automotive drive train application, the braking energy will be much greater than the accelerating energy for a much shorter time.

Electric regenerative braking in industrial applications is not known for being efficient. Generating and storing energy over a wide rpm and torque range is difficult. All systems have an operating voltage. When a generator rpm varies, so does the voltage output. The amperage varies with load. All the variable speed control electronic systems I have looked, at are not averaging much over 80% efficient driving a varying load over their operating speed range. I have not found any data on the efficiency of any regenerative system. In wind power the varying wind speed creates their power generation difficulty, most systems control the speed by varying the prop pitch. Some of the new systems are using power electronics, but the cost and efficiency has not proven to off set the cost of prop pitch control.

The most common application for hydraulic regenerative braking is in hydraulic elevators. Most have a hydraulic cylinder to raise the car, when letting the load down the flow pressure is diverted to accumulators. Hydraulic hybrid drives currently being developed use a swash plate pump/motor and valves to divert the flow and pressure to accumulators. Neither of these systems have great efficiencies base on the calculation I have done.

One of the greatest challenges in regenerative braking is converting low energy inputs to a higher energy level required for peek acceleration power.
For these reasons I do not think current electric or hydraulic hybrids will be a long term winners in saving energy.

In theory if all the kinetic energy could be captured and reused for reacceleration, the only power required for a vehicle is to overcome wind, and rolling resistance and climbing hills.

 

[GregLocock]

In automotive regen, typical claimed crude loop efficiencies are of the order of up to 60% for electrical systems and 80% for hydraulics. These are rather dodgy numbers as some mechanical braking is used as well, which has an efficiency of 0%. In practice it is not possible to size an automotive system so that it can capture the full braking power of the vehicle. So the system is sized to provide the maximum economic benefit in a given defined drive cycle, typically the EPA city cycle.

In this cycle approximately 1/3 of the energy supplied by the engine ends up in the brakes.

Cheers

Greg Locock

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