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Regeneration no longer just about braking

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January 1, 2009

Power Generating Shock Absorber
 Graphic: David Oxenreider

Power Generating Shock Absorber Graphic: David Oxenreider

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January 2, 2009 Recent developments in regeneration technology are almost ready for prime time. Both Hydraulic Hybrid Vehicles and Power Generating Shock Absorbers are both being field tested and may be soon headed for mass production. Transport company UPS has committed to purchasing seven "series" hydraulic hybrid delivery vehicles while Electric Truck, LLC has exclusively optioned commercial rights to a technology from Tufts University that uses Regenerative Shock Absorbers to recharge the batteries of any hybrid electric and electric-powered vehicle while it is driven.

Regenerative shock absorbers

The regenerative electromagnetic shock absorber uses an electromagnetic linear generator to convert variable frequency, repetitive intermittent linear displacement motion to useful electrical power. The regenerative electromagnetic shock absorber technology was developed by Tufts University engineering professor emeritus Ronald Goldner and colleague Peter Zerigian within the School of Engineering and received additional support in subsequent years from Argonne National Laboratory. While Goldner and Zerigian have patented the idea, it also appears that an almost identical concept was developed in the same period by David Oxenreider of Boiling Springs, PA, a design which took out Second Prize in the 2005 Emhart "Create the Future" Design Contest.

How it works

A conventional automotive shock absorber dampens suspension movement to produce a controlled action that keeps the tire firmly on the road. This is done by converting the kinetic energy into heat energy, which is then absorbed by the shock’s oil. The Power-Generating Shock Absorber converts this kinetic energy into electricity instead of heat through the use of a linear electric motor. The electricity generated by each PGSA can then be combined with electricity from other power generation systems (e.g. regenerative braking) and stored in the vehicle’s batteries.

The motor is usually a cylindrical 3-phase brushless permanent magnet linear electric motor that is sometimes referred to as a ServoRam. Early ServoRams were developed in the 1990s to replace hydraulic rams in entertainment motion simulators. Bose have also developed an Active Suspension System that uses linear stepper motors to replace standard shocks/springs. Bose claim they have been working on the software (algorithm as they call it) for 24 years (since 1980). The difference between the Bose system and power generating or regenerative shock absorbers is that the later retain standard coil springs to suspend the static load of the vehicle while Bose have deleted springs altogether.

Linear motors as replacement ‘shock absorbers’ are a much cheaper solution with more regenerative potential and have enormous potential in motorsport, where shock absorbers could be constantly variable. An electromagnetic shock absorber could be tuned to respond to virtually any input. With regenerative shock absorbers connected to a microprocessor system with any number of inputs such as on-chip gyro, accelerometer, ride height and steering angle a 4-shock system can actively control a vehicles pitch, roll and yaw.

Since the technology actively uses the weight of a vehicle for energy recovery, it could help speed the expansion of the hybrid and battery electric vehicle market from cars to vehicles of greater size, weight and payloads, such as SUVs, pickup and delivery trucks, mail trucks, school and city buses and other light and medium duty trucks

Hydraulic hybrid regeneration

The UPS "series" hydraulic hybrid delivery vehicles have a diesel engine combined with a unique hydraulic propulsion system, replacing the conventional drivetrain and transmission. The vehicle uses hydraulic pumps and hydraulic storage tanks to capture and store energy, similar to what is done with electric motors and batteries in a hybrid electric vehicle. In this case, the diesel engine is used to periodically recharge pressure in the hydraulic propulsion system. Fuel economy is increased in three ways: vehicle braking energy is recovered that normally is wasted; the engine is operated more efficiently, and the engine can be shut off when stopped or decelerating. The hydraulic series hybrid, originally developed in a laboratory of the US Environmental Protection Agency (EPA), uses a diesel engine/pump to pressurize and transfer hydraulic fluid to the rear drive pump/motor and/or high pressure accumulator. The hydraulic drivetrain replaces the conventional drivetrain and eliminates the need for a conventional transmission. UPS and the US Environmental Protection Agency (EPA) said the prototype vehicle had achieved a 45-50% improvement in fuel economy compared to conventional diesel delivery trucks.

Eaton Corporation began working with the EPA in October 2001 under a Cooperative Research and Development Agreement involving hydraulic hybrid systems and components. As part of Eaton’s role in designing and developing hybrid technologies, the company’s engineers were co-located at the EPA’s Ann Arbor facility. Eaton also earned a number of hybrid power system patents and continues to work on a number of other hybrid vehicles initiatives with UPS and others.

The EPA believes the technology can perform equally well in other applications such as shuttle and transit buses and refuse pick-up trucks. In 2007, the agency launched a project to develop hydraulic series hybrid systems for Class 6 port yard hostlers—the heavy-duty diesels that move goods and products from ships to trucks at ports.

Paul Evans

UPS hydraulic hybrid delivery vehicles video:

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