Riversimple aims to revolutionise city motoring

5 min read

Riversimple’s city car takes the idea of green motoring to new levels: it will only be available for hire, will be made in relatively tiny factories and its technology will be open to all. Stuart Nathan reports

Electric cars are very much in vogue at the moment. From the increasing numbers of hybrid cars on the road — from family workhorses to SUVs — to the government’s new focus on boosting the deployment of plug-in rechargeable vehicles, it seems sure that, somehow, electricity will be a major player in road transport in the coming decades.

One newcomer to the field, however, breaks all the rules. The Riversimple ‘city car’, an unassuming, even slightly squat two-seat runaround, uses hydrogen fuel cells as its power source rather than rechargeable batteries. The philosophy underpinning it is also strikingly different from the norm. It won’t be made in enormous factories. It will never be sold, only leased. And rather than being hedged around with protective patents and an army of lawyers, its technology is open source — available for anyone to look at and develop, in a similar way to much successful software.

Riversimple is the brainchild of former racing driver Hugo Spowers, who may be familiar to readers of The Engineer from his work on the Morgan LifeCar, another eye-catching hydrogen- powered roadster. But unlike the LifeCar, Riversimple isn’t designed to be a flashy sports car. Rather, it is specifically a city car — designed for short journeys, within a single city; powered by hydrogen from a purpose-built infrastructure; and with low emissions and efficiency as the cornerstone of its design philosophy.

‘Energy efficiency is going to become the overriding factor for transport: “How far can you go on one litre of fuel?”’ Spowers explained. ‘The key result of our technology is that the car is highly efficient: 30g of carbon dioxide well-to-wheel in the urban cycle, even using hydrogen that’s been produced from natural gas. That’s a quarter of the emissions of the lowest-emitting car on the market today.’

The design of the car was a group effort, with graduate students from Oxford University’s Energy and Power group, under Prof Malcolm McCulloch, working with the Life Cycle Engineering and Automotive Studies groups at Cranfield University on the engineering design and power electronics of the car; Singapore-based Horizon Energy designed the fuel cell. The consortium also includes BOC, which is planning the fuelling infrastructure, and funding has come from Sebastian Piech, a member of the Porsche family. The design philosophy was geared entirely around weight reduction, explained Tim Woolmer, a member of the Oxford team.

The original idea, Woolmer said, came from work published in the mid-1990s by Thammy Evans and Amory Lovins, transport solutions researchers at the Rocky Mountain Institute in Colorado. They theorised that efficient electric-drive systems could work in synergy with lightweight materials and an aerodynamic design to give large gains in efficiency. ‘The thinking was that if you make a lightweight car you increase the efficiency, but also if you have an electric drive with regenerative braking from all four wheels, you can improve efficiency by another 50 per cent,’ Woolmer said. ‘If you apply both together, removing weight wherever possible, you can get a tenfold increase in efficiency. So what we’ve ended up with is an ultralightweight car where everything — motors, power electronics, capacitors — has been designed for low weight.’

The car’s drive train doesn’t include a gearbox; hub motors in each of the four wheels are fed by a 6kW fuel cell and a bank of ultracapacitors, which is at the heart of the regenerative braking system. ‘Packaging everything was a major design constraint; we couldn’t take up space within the car for a motor,’ said Woolmer. ‘Putting the motors in the wheels was the best way of making use of space.’ The entire car weighs about 300kg, with the body made from composites; lack of engine and gearbox means the chassis can also be lightweight, as it doesn’t have to hold on to heavy metal components in the event of a crash.

The fuel cell is tiny — the Honda Clarity, a four-seater fuel-cell car uses a 100kW unit. This, explained Dolf Joekes of Horizon Energy, means the car doesn’t need to store large amounts of hydrogen and the fuelling stations can also work with a relatively small supply.

So how can the car operate with such a small power supply? The key to this, Woolmer explained, is the way the car will be driven and the way it uses and distributes power. In a normal car, the engine provides all the power, most of which is required for acceleration. Keeping the car at a cruising speed only uses 20 per cent of the engine’s power. But the Riversimple car, in another concept from the Rocky Mountain Institute, ‘decouples’ acceleration and cruise. All the power for acceleration comes from the ultracapacitors and these also receive all the power from the regenerative braking system; they can absorb some 30kW of power from braking and deliver 15kW in a 10-second burst for acceleration.

Because the car is designed only for driving within a city, an average driving cycle will include frequent spells of acceleration and braking, Woolmer said. ‘The ultracapacitor bank, which weighs about 20kg and sits under the seats, has bidirectional converters, which means it can push energy into the motors and receive it from them when the driver brakes. So in a driving cycle, the ultracapacitor actually supplies most of the power, charging up when you brake and powering the motors when you accelerate. The fuel cell just overcomes the losses in the vehicle systems and the aerodynamic drag and keeps it at its top speed. It’s been sized purely to allow the vehicle to cruise at 50 miles per hour.’

Alongside the new technology is a novel idea of how the car will be used. Rather than selling it, the car will be leased and leasing costs will include fuel. This makes the manufacturer responsible for running costs, maintenance and disposal; according to Spowers, this is an incentive for making the car as robust, reliable, long lasting and recyclable as possible. A Riversimple car should last for 20 years, Spowers said. In that time, it would be leased to several customers, with the lease cost decreasing each time. Initial leasing costs are envisaged to be around £200 per month, plus £0.15 per mile. ‘What hope have we as a sustainable industrial society if we’re based on rewarding the opposite of what we’re trying to achieve: resource maximisation rather than resource minimisation? We’re persuading people to keep their cars as long as possible rather than changing them as often as possible,’ Spowers said.

As the cars are for local use, Spowers plans to launch them city by city, and each city will also have its own manufacturing facilities. He believes one reason for the automotive industry’s problems is the investment embodied in very large plants to make high volumes of steel cars. ‘The factories to build our cars, from advanced composites, will be about a hundred times smaller than existing car plants; a network of a large number of small plants,’ he said. ‘This allows much greater resilience in fluctuating economic circumstances and better flexibility in customising the products to deliver what different regions and niches really need.’

Spowers and the team have now produced their prototype car. They will soon build 10 cars for testing over the course of a year, then use this experience to build 50 further prototypes for field testing in a small city such as Oxford. BOC is working on designing the infrastructure for this trial.

The local approach goes alongside the open-source IP philosophy, in which Riversimple has donated the designs for the car to the 40Fires Foundation, an organisation that will oversee the distribution of the designs and will facilitate collaboration. The open-source model is borrowed from software and, it is hoped, will lead to faster and more radical development of the design and technology, as board member Christian Ahlert explained: ‘We’ve seen this speed and imagination in the development of Linux software and at the same time we’ve seen for a couple of years that other areas are starting to experiment with open-source hardware engineering in projects ranging from laptops to mobile phones and computer chips.’

Open source doesn’t mean a free-for-all, however. ‘You’re not giving everything away for free: that’s a misconception. What you’re trading is a licence that specifies how others can contribute and build on what you make available, but it also restricts what people can do with it. As soon as you want to manufacture the car or component and engage in a commercial activity, we’d have a separate licence agreement with the developers.’

Although 40Fires is still being set up, once it is operational its website will include a collaborative web platform with online open-source CAD tools. ‘This sort of highly collaborative endeavour simply wasn’t feasible until you had the internet,’ Ahlert said. ‘You find there are many people who have something to contribute, from retired engineers to small companies anywhere in the world. We really do welcome contributions and expressions of interest from a wide variety of engineers: automotive, electrical/electronic and engineers experienced in workflow design.’