“Re-inventing” the in-wheel drive system

A team of British and American entrepreneurs and engineers would like you to reconsider everything you know about in-wheel motors – and take a look at their approach which, they believe, has turned past designs “inside out”.

Protean Electric is an advanced technology company that has redesigned and re-engineered the in-wheel electric motor. Protean’s approach – turning the wheel motor “inside out” and putting the rotor on the outside – gives the motor great torque density, and allows Protean to package the inverter and power electronics inside each motor to improve vehicle packaging. These in-wheel motors improve fuel economy and performance, and can be easily integrated into a broad range of vehicles. Protean’s system can increase fuel economy by over 30% depending on the size of the battery and the driving cycle. Protean is based in the United States and the United Kingdom.

Automotive Industries (AI) asked Bob Purcell, Protean Electric’s chief executive officer to explain how advanced the technology is for an in-wheel electric drive. 

Purcell: There is simply nothing else like it. We turned that model inside out, putting the rotor on the outside and the stator and electronics on the inside. That simplicity of design creates more power density per motor and much simpler vehicle integration. Rather than using one large inverter to control the motor, Protean Electric has a patented distributed architecture that uses eight self-contained sub-motors that work together. Delivering 81kW (110hp) per in-wheel motor, it’s the highest power density drive system we know of and it all fits in a conventional 18-inch road wheel. 

AI: Please tell us about your most recent vehicle announcement with BRABUS, the luxury performance tuner.

Purcell: This was really an exciting project for us. BRABUS is the largest independent automobile tuner in the world.  They make very exclusive high-performance automobiles for very discerning customers. We partnered with them to build two different kinds of performance drivetrains, both displayed at the 2011 Frankfurt Motor show. The first BRABUS EV sedan, called the “High-performance Four-wheel-drive Full Electric Car,” is based on the Mercedes-Benz E-Class. Its’ all-new EV system has a peak combined 320 kW (430 hp) and 3,200 Nm (2,350 ft.-lbs.) torque from pure electric power using four direct-drive Protean Electric motors, one in each wheel.  The second BRABUS is a hybrid drive vehicle, with two in-wheel motors and an internal combustion engine, all driving the rear wheels. Each in-wheel motor adds 80 kW (110 hp) and 800 Nm (590 ft.-lbs.) of peak torque to each rear wheel. This gives the sedan a combined electric motor and internal combustion engine acceleration of 0-100 km/hr (0-62 mph) in 7.4 seconds.  The car is impressive.  It will accelerate from 60-120 km/hr (37-75 mph) of 5.6 seconds. This is the new definition of performance, done efficiently and responsibly.

Partnering with BRABUS on these vehicles was very cool for us and really demonstrates the flexibility and diversity of our in-wheel motors. 

AI: What response did the Ford F150 pick-up truck retrofitted with your in-wheel drives evoke at the SAE World Congress in April this year in Detroit? 

Purcell: That was a great opportunity for Protean Electric. It gave the international forum of engineers and business people a chance to see how easy it is to integrate into a vehicle. Near our display, we featured the Ford F150 pick-up during the ride and drive sessions and I believe everyone was impressed with the quiet performance of our direct drive motor system. 

AI: What has been the industry response to the Vivaro Plug-In Parallel? 

Purcell: We have had a sensational industry response to the Vivaro ever since we showed the vehicle in May at the 2011 Michelin Challenge Bibendum in Berlin. Fleets especially love the concept. The Vivaro is powered by a conventional diesel engine for the front wheels and two Protean Electric motors retrofitted to the rear axle. The driver has the advantage of being able to switch between multiple operating modes: two- or four-wheel drive operation, or an electric torque assist Through-The-Road-Hybrid. The Protean-equipped Vivaro van can achieve an effective 60 percent fuel economy improvement in charge depleting mode (electricity + diesel) as compared to charge sustaining mode (diesel only). Source:  SAE “Recommended Practice for Measuring the Exhaust Emissions and Fuel Economy of Hybrid-Electric Vehicles, Including Plug-in Hybrid Vehicles” (J1711 JUN2010).

AI: What has Protean drawn from the data taken as a result of the partnership with Millbrook testing ground with the Vauxhall Vivaro TTRH (through the road hybrid)? 

Purcell: The main benefit of the testing has been to get real world third party validation of our technology and systems. We have now run for over 10,000 km, including a 100-hour Pave simulation, with very few problems. The vehicle has also gone through a comprehensive set of prototype validation tests and in most cases, passed with flying colors. That’s about where we want to be. We are on a path to be fully certified and validated to automotive standards. So, in short, we have learned a lot about the control system integration and how our IP is involved in developing through-the-road plug-in hybrids like the Vivaro. 

AI: What are the benefits for OEMs in using the Protean Drive? 

Purcell: The Protean Electric motors offer several advantages. The first is about speed to market and avoiding development costs. Since the motors and motor control electronics are in each wheel, there are few if any modifications necessary for the body structure, transmission, or drivetrain components. This avoids expensive re-tooling of large body panels and drivetrain components and minimizes disruption in the vehicles final assembly process. If the Protean Drive system is used to augment the existing powertrain, there is no need for changes to major engine emission components. Development engineers can use the Protean Drive on board a vehicle with a conventional IC engine, allowing them to make the IC engine smaller and more fuel efficient. Manufacturers can think about creating a portfolio of powertrains, from hybrids to PHEVs to EVs, simply by resizing the battery and using the same vehicle and the same in-wheel motor drivetrain technology. Finally, with the motor out of the way and with no drive shafts or gear boxes or differentials, just think how automotive designers now have new freedom like never before to create exciting vehicles. 

AI: What do you think is the future of hub-mounted motors? 

Purcell: With the capability of today’s power electronics and the packaging innovation of Protean Electric’s distributed architecture design, the time is right for in-wheel motors to be used in high volume. The use of electric motors to improve the fuel efficiency of cars and trucks is going to increase exponentially. The low cost and high power density of the Protean Drive in-wheel motor design is well suited for the near-term introduction of in-wheel motors in new vehicles and the retrofitting of existing vehicle fleets. 

AI: What is Protean’s strategy in popularizing its technologies in the USA and Europe? 

Do you think markets outside these regions are also ready for the Protean Drive?
Purcell: We have active programs underway in the USA, Europe and Asia. We believe the 81kW (110hp) motor designed for an 18-inch road wheel is the best place to start. That size and power is applicable to a wide range of retail and fleet vehicles used in all three regions. The fuel saving benefits of the Protean Electric in-wheel motor will encourage the retrofitting of light commercial vans and trucks in the near-term. The motor’s power density makes it also well suited to provide enhanced performance for vehicles for both Europe and the USA markets. Beyond that, we see interest ranging from the most common cars to special applications like delivery vans, EVs, taxis and police cars.