MIT Students Develop Hydraulic Energy-Generating Shock Absorbers
13 February 2009
|GenShock prototype. Click to enlarge.|
A team of MIT undergraduate students has invented a shock absorber that harnesses energy from small bumps in the road, generating electricity while it smoothes the ride more effectively than conventional shocks. MIT Senior Shakeel Avadhany and his teammates say they can produce up to a 10% improvement in overall vehicle fuel efficiency by using the regenerative shock absorbers.
Their prototype shock absorbers use a hydraulic system that forces fluid through a turbine attached to a generator. The system is controlled by an active electronic system that optimizes the damping, providing a smoother ride than conventional shocks while generating electricity to recharge the batteries or operate electrical equipment.
Another Boston-area startup, Electric Truck LLC, has exclusively optioned commercial rights to a regenerative electromagnetic shock absorber technology developed by Tufts engineering professor emeritus Ronald Goldner and colleague Peter Zerigian within the School of Engineering and which received additional support in subsequent years from Argonne National Laboratory. Their regenerative shock absorber uses an electromagnetic linear generator to convert variable frequency, repetitive intermittent linear displacement motion to useful electrical power. (Earlier post.)
In testing so far, the MIT students found that in a 6-shock heavy truck, each of their regenerative shock absorbers could generate up to an average of 1 kW on a standard road—enough power to completely displace the large alternator load in heavy trucks and military vehicles, and in some cases even run accessory devices such as hybrid trailer refrigeration units.
AM General, the company that produces Humvees for the army, and is currently working on development of the next-generation version of the all-purpose vehicle, is interested enough to have loaned the MIT team a vehicle for testing purposes.
They filed for a patent last year and formed a company, called Levant Power Corp., to develop and commercialize the product they call GenShock.
The team is currently doing a series of tests with their converted Humvee to optimize the system’s efficiency. They hope their technology will help give an edge to the military vehicle company in securing the expected $40 billion contract for the new army vehicle called the Joint Light Tactical Vehicle, or JLTV.
The team has received help from MIT’s Venture Mentoring Service, and has been advised by Yet-Ming Chiang, the Kyocera Professor of Ceramics in the Department of Materials Science and Engineering and founder of A123Systems, a supplier of high-power lithium-ion batteries.
The new shocks also have a fail-safe feature: If the electronics fail for any reason, the system simply acts like a regular shock absorber.
The group, which also includes senior Zachary Jackowski and alumni Paul Abel '08, Ryan Bavetta '07 and Vladimir Tarasov '08, plans to have a final, optimized version of the device ready this summer. Then they will start talking to potential large customers. For example, they have calculated that a company such as Wal-Mart could save $13 million a year in fuel costs by converting its fleet of trucks.
"Their prototype shock absorbers use a hydraulic system that forces fluid through a turbine attached to a generator"
Isn't there a better non-mechanical method other than a turbine?
Posted by: Peace Hugger | 13 February 2009 at 04:18 AM
Sounds great - how much will it cost?
Would it be worth adding to domestic cars, or just to heavy vehicles - sounds like it could reduce the alternator load a great deal.
All down to cost.
Posted by: mahonj | 13 February 2009 at 04:18 AM
In the course of my day job, I have analyzed and studied active and semiactive suspension systems as an alternative to passive suspensions like we now have on most cars.
Semiactive suspensions are basically, shock absorbers which can vary their damping coefficient rapidly, so as to offer resistance to motion when we want it, but not when we don't. Said devices can use variable orifices, or they may utilize electrorheological or magnetorheological fluids whose viscosity may be varied rapidly simply by varying an applied electrostatic or magnetic field. Magnetorheological fluid based shock absorbers have been used on some cars, i.e. Cadillac sport sedans.
The ultimate in technological sophistication, suspension-wise, is a fully active system where we input energy into an actuator so as to counter unwanted body motion. Such actuators may be hydraulic or electromechanical. Ford Motor Company, years ago, patented an electromechanical active suspension actuator. Bose, the outfit known for consumer electronics, also developed an electric active suspension actuator. Active suspensions require energy input, and have been criticized for costing too much and compromising fuel economy because of their energy requirements.
Suppose one were to take an electromechanical active suspension actuator, and connect the wires to a resistance, and then apply motion to it. It would act as a generator, and the resistor would get hot. By varying the resistance, one could vary the effective coefficient of damping. Now suppose we take the electric energy thus generated, and use it for some useful purpose instead of just converting it to heat in a resistance. Voila! You have an electromagnetic regenerative shock absorber.
What those MIT students came up with, is a hydraulic regenerative arrangement. A purely electric arrangement like I described, would attain semiactive suspension functionality without hydraulic fluid and regenerate energy that would otherwise be wastefully converted to heat.
I think said idea is worth exploring.
Posted by: Alex Kovnat | 13 February 2009 at 05:03 AM
I'm a little confused here: a vehicle is traveling forward (x axis) and encounters a bump in the road which drive the wheel up (y axis). The spring/shock absorber combo absorbs this energy and then must return said energy in the y axis in order to re-level the car, no?
Posted by: GreenPlease | 13 February 2009 at 05:54 AM
@GreenPlease and the group:
Some clarification is in order regarding suspension systems. There are passive systems, semi-active suspensions, and fully active suspensions. The first, is just your basic combination of spring, mass and damper. Actually even a simplified model requires an unsprung mass, sprung mass, a spring and damper (shock absorber) between said masses, and a mathematical model for the tire which could be just a spring, or both a spring and a damper.
A semiactive suspension uses a spring and a damper whose damping coefficient is rapidly variable. A computer controlled system, by varying the damping coefficient in the right manner at the right time, can result in improved comfort for the passengers by reducing undesired body motion. In a semiactive system, there is no energy input except for that required to adjust the damper rapidly.
With a fully active suspension system you need an actuator which provides a force input to the unsprung mass/sprung mass system to counteract unwanted sprung mass motion. This system requires external energy, which comes from the engine in one form or another. The result is, you compromise fuel economy because an active suspension's power demand is an added load on the engine.
With passive and semiactive systems, the spring (coil or leaf) compresses to absorb bumps, then re-levels the car. You need a damper of one form or another, to dissipate energy that would otherwise result in the car bouncing up and down repeatedly every time you hit a bump in the road.
What I proposed in my earlier post and what the MIT students are proposing, is a semiactive system which feeds suspension energy into the vehicle's electrical system instead of dissipating suspension energy as heat, as a conventional shock absorber does and as a semiactive system also does but in a more sophisticated manner.
An electric active suspension actuator can transfer energy in either direction, i.e. from the vehicle electric system to the suspension, or the other way around. We can operate said device in either fully active mode, or in semiactive mode. In the latter mode, we get the benefits of semiactive suspension operation without the power consumption of a fully active suspension. In fact with such an arrangement, we feed a little energy into the vehicle power system, so we should get a slight increase in fuel economy.
Posted by: Alex Kovnat | 13 February 2009 at 07:48 AM
You are correct. Suspension is made up of two components, a spring and a damper. The spring (and the sway-bar) return the car to level. It is energy stored in the spring during compression that drives the return stroke. In current systems the damper absorbs energy during compression of the suspension (energy that comes out of the forward momentum of the car), and during the return stroke (when energy comes out of the spring).
This system could be much more simple were it not for a minefield of patents. Instead of a hydraulic pump as a damper, you could simply have a magnet being pushed through a series of coils. The moving electric field would induce a current in the coils, which could be rectified and sent directly to a battery. This would basically be a linear electric motor acting as a generator.
Posted by: Nat Pearre | 13 February 2009 at 07:55 AM
This is a brilliant idea! Esspecialy for any place with significant frost heaves like here in Canada! The fact that they are getting significant amounts of power out of it is great, normally this energy is lost as heat so why not?
Now many of you are suggesting the logical next step which is a fully electromagnetic regenerative shock absorber but the current hydraulic unit is a good start. They mention that if the electronics fail somehow this still functions as a regular shock absorber, very important. A fully electromagnetic unit would not have this backup. Think of it like regenerative brakes, with wheel motors you theoretically don't need mechanical brakes any more right? I doubt we will see an electric car with no mechanical brakes anytime soon though, probably never. We may see a car with electromechanical shocks though, but this is a good incremental step. I imagine the magnets and wiring required for a straight linear electromagnetic shock with enough damping force would be rather large, heavy and expensive, any ideas? Unless some levers/gearing are used to turn it into rotational motion. This is a great start though and I hope they can develop it further without too much patent hassel etc.
Posted by: Jesse 67 | 13 February 2009 at 10:01 AM
Great idea, I'll take 4 to go.
Posted by: ai_vin | 13 February 2009 at 11:45 AM
The fact that chose to do it through an hydraulic appraoch is rather surprising but that's a brilliant idea and achievement indeed. On overwhole when you sum up, start and stop, regenerative braking, waste damping recovery and also waste heat recovery you are talking about big saving
Posted by: Treehugger | 13 February 2009 at 06:34 PM
A more ingenious way of capturing energy from an automobile would be to invent a cam system on the wheels that would rotate (think spinner hubcaps), creating energy very similar to how automatic watches wind themselves up. The government has partnered with a startup experimental company to capture energy of soldiers as they march, to charge up battery packs for their radios and other small electrical devices. Similar inventions could be applied to any vehicle, such as cars, motorcycles, and bicycles, and even treadmills or elliptical machines.
Posted by: richw930 | 14 February 2009 at 04:37 AM
Waht you propose is called "perpetual motion" and consequently doesn't work, you will create more friction than the energy you get my friend. What they propose here is totally different, they tap in wasted energy, if you start to tap in the non wasted energy then it doesn't make any sense. Automatic watches tap into non wasted energy but a tiny winy amount so you don't feel it, but strictly speaking you spend more energy to move your arm when you wear an automatic watch than when you wear a battery powered watch.
Posted by: Treehugger | 14 February 2009 at 11:30 AM