Digital Displacement

Driving through mountains is a huge frustration for me. I use so much fuel going up, and wear out the brakes when going down.

I’ve been thinking that the perfect vehicle for paragliding should have a system of regenerative braking, which turns the energy from braking back into useable energy to push you along and up the hills.

The only way to do this, that I was familiar with, was to use an electric drive train, where the motor on the wheels can be used as a generator which slows the vehicle down and charges the battery.

Many trains have a diesel electric drive train, in which a diesel generator creates the electricity which drives a motor connected to the wheels. This seems like an unnecessarily complicated approach; when you have a diesel engine spinning away, it would seem to be more logical to connect it to the wheels rather than a generator connected to a motor connected to wheels.

In fact diesel-electric is more efficient, because there are less transmission losses (there’s no gearbox) and it allows the diesel engine to run at the speed where it is most efficient. Diesel engines are very inefficient outside a narrow rev range.

So the obvious answer is diesel-electric hybrid truck, or in my case veg-electric hybrid, with regenerative braking. I could take the gearbox out, and attach a generator in its place, then attach a motor to the differential at the back where the drive shaft would be. The Toyota Prius is able to capture and reuse about 50% of the braking energy.

Unfortunately the components required to control and power manage an electric vehicle are hugely expensive, and fitting them is much more complicated than just bolting on some off the shelf parts. But in theory it could improve the efficiency significantly, and I’d love to give it a try, because if there is one thing this bus is missing, it’s efficiency.

Last month Iain got in touch through Facebook and told me about "Digital Displacement" technology which I’d describe as a “diesel-hydraulic” hybrid system. Instead of a generator, a hydraulic pump is attached to the engine. This then creates hydraulic pressure, which can be stored in a pressure tank full of nitrogen or directed to a hydraulic motor attached to the wheels. The clever part of the system, which has been designed by Artemis Intelligent Power in Scotland, is the fast reacting valves that control how the hydraulic pressure is directed. The valves make the motor much more efficient than anything that’s gone before. The system is computer controlled, so that it acts as a variable speed gearbox. The engine always runs at optimum revs for the power required to move the truck along, and the speed is computer controlled by distributing the pressure to the sophisticated drive motor.

But best of all, the flow of pressure can be revered. The motor can be turned into a brake converting the energy from slowing the truck down into hydraulic pressure, which is stored and subsequently used to drive the car again. It’s much more efficient than an electric regenerative system, capturing and reusing 85% of the braking energy, because moving and storing energy at the high rate a braking vehicle generates it, is easier to do with hydraulic pressure than it is with the high currents generated and the batteries of an electrical system.

It’s a system that’s ideal for vehicles in stop-start driving scenarios, and the best energy savings will be on large vehicles, for instance bin-lorries and busses. Currently the technology has been sold to Bosch-Rexroth who will no doubt trial and develop reliable components first for this heavy vehicle market and then hopefully roll it out for smaller vehicles like cars if the energy and cost savings can be shown to be worthwhile.

There are other advantages over diesel-electric too. The components are lighter, and there isn’t the associated environmental impact of battery manufacture and ultra-capacitors burning out.

Using this gearbox on a large saloon car, Artemis have shown certified fuel savings of around 40%. This is one of those rare technologies that make a massive leap forward. In principle it’s a technology that can be retro fitted to any vehicle, especially trucks. I’ve been in touch with Artemis to ask if they have any components I could trial. The answer was an understandably lukewarm no, but I'm going to persist. This is prototype stuff and I suspect they don't have a license for road going vehicles anymore. I’m trying to get hold of people at Bosch to ask them too but I doubt they will want to let me test out the technology at this early stage, when they have everything to lose if prototype components are seen to go wrong.

The energy storage capacity needed to capture the energy of braking when driving down through mountains is much bigger than that for stop-go traffic so I’m still unclear how big the pressure tank would need to be to make the best use from the slow ongoing breaking energy of my 6 tonne truck descending from the Himalayas.

At the very least I hope the next Biotruck, Biotruck III, will be a Veg-Hydraulic hybrid designed for a tour of the world’s mountains.