By Josh Cosford, Contributing Editor
The automotive industry is leaving no stone unturned as it explores every possible technology and advancement that can improve performance while reducing CO2 emissions. Hybrid and electric vehicles have been employing regenerative braking systems that recapture kinetic energy through a motor generator rather than convert the vehicle’s inertia into heat, as done by the brakes. So effective is regenerative braking that a hybrid car’s fuel economy is typically better in the city than on the highway.
Electric vehicles are so deep with regeneration that manufacturers offer one-pedal driving for nearly every EV available today. When driving with one pedal, down means go and up means slow – as you lift off the gas pedal (electron pedal?), the motors behave as generators, converting the kinetic energy back into electrons, which temporarily replenish the battery.
Motor generators give and receive torque, but energy can be captured if inertia exists. Can we capture energy from wind to waves or from hydro dams to … shock absorbers? Believe it or not, shock absorbers are linear brakes, so why let them oscillate within oil, creating only heat when they can be directing that energy back into the system?
The idea of regenerative suspension is not new. Various manufacturers have been experimenting with electrohydraulic suspension systems since the early oughts, and when they realized we could use pumping systems into the dampers, we could use dampers to pump right back. Over a smooth road, you’d be surprised at just how much suspension oscillation is occurring, so bumpy roads are downright spilling over with potential energy.
Even as recently as 2015, Audi worked on their eROT system for electromechanical suspension that could direct kinetic energy back into the electrons that could be used to charge the battery, saving demand from the alternator. However, they found that, on average, only 100-150 watts could be recuperated; not a huge amount, but perhaps worth further development.
However, because passenger vehicles primarily travel on smooth roadways, what if you could capture the energy otherwise dissipated from the oscillation of very heavy vehicles driven off-highway, like mobile machinery? Many modern machines, such as farm tractors, Figure 1, meant for occasional road use, use hydropneumatic suspension systems using accumulators. Modifications to the circuit, which could be as simple as a series of check valves and an additional accumulator, could capture the high-pressure spikes inside oil-filled dampers.
Hydraulic regeneration is already a thing, with many manufacturers offering solutions that enable stop and start-intensive vehicles, like garbage trucks and loaders, a powerful solution to capture kinetic energy. Equipped with a pump/motor that can switch between energizing an accumulator under braking to driving the wheels, this system provides a huge boost of torque to get these heavy vehicles off the line.
Such a system would provide benefits to any large vehicle through its suspension system as well. The benefit of a hydraulic accumulator is the possible massive load of pressure and flow capacity over a short period, suitable to provide starting torque to reduce fuel load over full-throttle driving. There’s no reason such systems couldn’t operate alongside electric or hybrid mobile hydraulic machinery since heavy machinery will still need oil-based suspension dampers for the foreseeable future.
