Kinetic Energy Recovery Systems (KERS) technology takes a moving vehicles kinetic energy, which is otherwise wasted during braking, stores it, then releases it back into the drive train as the vehicle accelerates. This is a form of regenerative braking. There are three main types of KERS units - mechanical, electical, and hydraulic - but all are designed to boost acceleration while delivering lower fuel consumption, and therefore less CO2 emissions, independent of the vehicle's engine. The first commercial systems have been developed by three UK companies: Flybrid Systems, Torotrak, and Xtrac.
Basically, the mechanical system consists of a flywheel connected by a continuously variable transmission (CVT) to the drive train. This is not an ordinary CVT with belts and pulleys to vary the gear ratios but a toroidal type that uses discs, power rollers and a microscopic film of long-molecule traction fluid that separates the two at their contact points. Moving the CVT towards a gear ratio that would speed the flywheel up enables it to store energy, while moving towards a ratio that would slow it down allows it to release energy. A hydraulic clutch separates the drive if the flywheel's revs exceed the system's limits.
The ratio adjusting mechanism is known as a variator and includes an input disc and an opposing output disc. Each disc is formed so that the gap between them creates a toroidal cavity. There are two or three rollers inside each cavity, depending on torque capacity, which are positioned so that the outer edge of each roller is in contact with the toroidal surfaces of the input and output discs. As the inout disc rotates, power is transferred via the rollers to the output disc, which rotates in the direction opposite to the input disc.
The angle of the roller determines the ratio of the CVT, so any change in the angle of the roller results in a change in the ratio. Thus, with the roller at a small radius (near the center) on the input disc and at a large radius (near the edge) on the output disc, the CVT produces a 'low' ratio. Moving the roller across the discs to a large radius at the input disc and corresponding small radius at the output produces the 'high' ratio, and provides the full ratio sweep in a smooth, continuous manner. The system has a mechanical efficiency of > 90%. For more details and a photo of a representative system, go to:
http://www.gizmag.com/go/7396
In the mechanical system, energy is stored in the flywheel and released into the drive train directly. A consensus seems to be emerging that the mechanical approach seems to trump the the others, at the moment, in terms of weight, size, and cost.
In the electrical system, essentially the braking energy is harnessed by storing it in super capacitors or batteries, and then releasing it back into the drive train through a motor and flywheel. Although more expensive and tending to be larger and heavier than a mechanical unit, it offers more flexibility in placing the various components around a vehicle which is important when weight distribution is a factor (as in racing vehicle use) which will presently be made clearer.
The principle behind hydraulic KERS units is to reuse a vehicle's kinetic energy by conducting pressurized hydraulic fluid into an accumulator during deceleration, then conducting it back into the drive system during acceleration. However, there are several drawbacks here. One is the relatively low efficiency of rotary pumps and motors. Another is the weight of of incompressible fluids. A third is the amount of space needed for the hydraulic accumulators and the necessity to accomodate their awkward shapes. While none of this may matter much in commercial vehicles, this option is obviously unsuitable for use in road or racing cars.
As KERS technology is about to undergo intensive implementation and development in Formula 1 racing, the next post will be devoted to that project.
Happy Motoring!
Basically, the mechanical system consists of a flywheel connected by a continuously variable transmission (CVT) to the drive train. This is not an ordinary CVT with belts and pulleys to vary the gear ratios but a toroidal type that uses discs, power rollers and a microscopic film of long-molecule traction fluid that separates the two at their contact points. Moving the CVT towards a gear ratio that would speed the flywheel up enables it to store energy, while moving towards a ratio that would slow it down allows it to release energy. A hydraulic clutch separates the drive if the flywheel's revs exceed the system's limits.
The ratio adjusting mechanism is known as a variator and includes an input disc and an opposing output disc. Each disc is formed so that the gap between them creates a toroidal cavity. There are two or three rollers inside each cavity, depending on torque capacity, which are positioned so that the outer edge of each roller is in contact with the toroidal surfaces of the input and output discs. As the inout disc rotates, power is transferred via the rollers to the output disc, which rotates in the direction opposite to the input disc.
The angle of the roller determines the ratio of the CVT, so any change in the angle of the roller results in a change in the ratio. Thus, with the roller at a small radius (near the center) on the input disc and at a large radius (near the edge) on the output disc, the CVT produces a 'low' ratio. Moving the roller across the discs to a large radius at the input disc and corresponding small radius at the output produces the 'high' ratio, and provides the full ratio sweep in a smooth, continuous manner. The system has a mechanical efficiency of > 90%. For more details and a photo of a representative system, go to:
http://www.gizmag.com/go/7396
In the mechanical system, energy is stored in the flywheel and released into the drive train directly. A consensus seems to be emerging that the mechanical approach seems to trump the the others, at the moment, in terms of weight, size, and cost.
In the electrical system, essentially the braking energy is harnessed by storing it in super capacitors or batteries, and then releasing it back into the drive train through a motor and flywheel. Although more expensive and tending to be larger and heavier than a mechanical unit, it offers more flexibility in placing the various components around a vehicle which is important when weight distribution is a factor (as in racing vehicle use) which will presently be made clearer.
The principle behind hydraulic KERS units is to reuse a vehicle's kinetic energy by conducting pressurized hydraulic fluid into an accumulator during deceleration, then conducting it back into the drive system during acceleration. However, there are several drawbacks here. One is the relatively low efficiency of rotary pumps and motors. Another is the weight of of incompressible fluids. A third is the amount of space needed for the hydraulic accumulators and the necessity to accomodate their awkward shapes. While none of this may matter much in commercial vehicles, this option is obviously unsuitable for use in road or racing cars.
As KERS technology is about to undergo intensive implementation and development in Formula 1 racing, the next post will be devoted to that project.
Happy Motoring!
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