Hybrid technology is all the rage these days, from golf clubs to Formula One race cars. When we think hybrid in automotive terms, we usually assume an energy storage system using batteries and motors.
If you really think of it, hybrid systems are load leveling devices.
Most power plants, from diesels to rocket engines operate most efficiently in a steady-state mode. In automotive applications however, steady-state conditions are strictly an open road proposition.
For the energy wasting stop-and-go driving cycles, it’s common practice to run electric motors in reverse through regenerative braking and charge a battery or capacitor to recycle the energy on acceleration.
There are other ways to store and recycle the energy however.
A company in Loveland Colorado called Lightning Hybrids uses hydraulics installed in medium and heavy-duty trucks and buses to achieve the same end.
It's conceptually simple: when decelerating, a hydraulic pump pressurizes an accumulator. When accelerating, that stored high pressure fluid is used to drive a hydraulic motor propelling the vehicle.
One advantage of the system is that it does not have to be integrated into the vehicles primary powertrain. In medium and heavy-duty applications for example, it could be applied to a tag axle or even on a trailers axle assembly. That also makes it a candidate for retrofiting to existing vehicles.
The automotive industry calls this a parallel system, compared to a series system.
Modern locomotives are series devices: a diesel drives a generator which powers an electric motor. For moderate light vehicles like the BMW i3, the internal combustion engine is simply an onboard charger for an electric drivetrain.
Another possibility is to use a modified form of conventional internal combustion drivetrain. In this scenario the flywheel or torque converter assembly becomes the Armature or rotor of an electric motor generator set.
This would be the electrical equivalent of the hydraulic system with a capacitor or battery acting as electrical accumulator, spinning up a conventional transmission on acceleration. For internal combustion engines this is really useful, since they're most efficient when operating under a constant predictable load which is far from conditions in urban stop-and-go traffic.
Could a hydraulic system like Lightning Hybrids device work on light vehicles as well as trucks? It might be possible, especially using some form of fiber wound composite accumulator that could hold substantial pressure without excessive weight.
Keep in mind this would be strictly a mild hybrid setup, useful mainly for load leveling a combustion engine powertrain. It's unlikely that it will be possible to store enough pressurized hydraulic fluid to give a vehicle significant range as a stand-alone system.
But even in a mild hybrid setup, there are knock on benefits to hydraulics.
Like other regen energy recovery systems, brakes can be made smaller, lighter and with a load leveling the fact on the engine, power plants can be redesigned to operate more efficiently over a narrower RPM band since significant torque off idle will not be a strict necessity.
Of course all this means lower fuel consumption and reduced emissions, which is ultimately the point of the whole exercise.
Lightning Hybrids claims that their tests show an 18 percent decrease in CO2 emissions compared to similar baseline vehicles with conventional diesel systems and up to 35 percent improvement in fuel economy.
In the end, it all may come down to politics.In Europe for example, there is considerable pressure to regulate vehicles on an emissions per mile basis or even outright bans on internal combustion engine vehicles in urban centres.
For the freight and package delivery industries, finding a way to get goods into those urban centres will not just be about efficiency, will be about environmental performance as well. A lot of things have been tried to make hybrid motor vehicles, from super capacitors to large flywheels.
I love the mechanical elegance and old-school charm of hydraulics, but I am betting the future is electric with hybrids as the motive power energy source of the future. Regardless of the price of oil.
What are your thoughts? Let us know in the comments below.
Learn more about Lightning Hybrids here.