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Protean Electric and FAW-VW developing production-intent electric propulsion system with in-wheel motors

Protean1
Cutaway of the Protean Electric in-wheel motor. Click to enlarge.

In-wheel electric drive developer Protean Electric is partnering with FAW-Volkswagen Automotive Co., Ltd. (FAW-VW) in China to develop a new electric propulsion system that will include Protean Electric’s Protean Drive with intent towards a demonstration vehicle program and production.

FAW-VW will create a new rear-wheel drivetrain for an electric vehicle (EV) based on the new Bora compact sedan, utilizing two Protean in-wheel motors. This cooperation began several months ago; all bench testing, engineering calibration and on-site application support is expected to be completed within a year. Protean Electric will also assist FAW-VW in the development of safety and vehicle controls that can be applied to additional vehicle programs.

This is a two-phase project that will capitalize on the torque and packaging freedoms that Protean Drive can bring to an automaker. Our technology will return the space to the new Bora vehicle platform that was formerly occupied by an in-board motor and powertrain.

—Kwok-yin Chan, CEO of Protean Holdings Corp.

Protean Electric introduced its production in-wheel motor at the 2013 Society of Automotive Engineers World Congress in Detroit. Volume production is targeted to begin in 2014, out of Protean’s new manufacturing facility in Liyang, China.

The permanent magnet synchronous motors reside in the space behind the wheel. Protean’s new production motor provides a 25% increase in peak torque compared with the previous generation’s design and can deliver peak output 1,000 N·m (735 lb-ft) and 75 kW (100 hp), with 700 N·m (516 lb-ft) and 54 kW (72 hp) continuous. (Earlier post.) Protean says that its new production motor provides the highest torque and power density of any leading electric propulsion system.

In a paper presented at the EVS 27 conference in Barcelona, Gareth Roberts from Protean and Alessandro Galeazzi from SKF Automotive (a strategic partner of Protean), noted that:

The performance gain with respect to other more conventional arrangements is due to the full integration and synergies created with the mechanical components and in particular the wheel bearing. The final performance is connected to the ability of the wheel bearing to provide the required stiffness that controls the reduction of the air gap between the motor rotor and stator.

… There are three geometric factors that make up the motor air gap: the diameter Z, the motor length X and air gap length Y. For motor performance, it is desirable to maximise the diameter and motor length and minimise the air gap length.

The control of this air gap under different operating conditions is vital to ensuring efficiency and high levels of performance targeted by the In-Wheel motor. Road loads in their worst cases however, represent a significant challenge in maintaining the optimum level of air gap, hence the need to tightly control its variation. Furthermore, there is a risk of magnets touching the wound teeth if too much variation is allowed, with serious consequences for mechanical damage, performance and durability of the In-Wheel motor. The wheel bearing design and in particular the tilting stiffness, influence the design of the motor length and airgap length, which in turn influence the motor performance.

Protean engineers inverted the conventional motor design; the rotor is on the outside and the stator on the inside. This improves performance, makes it compact, and provides space inside the motor for power electronics and controls, the company says.

Each in-wheel motor, with an operating range of 200 - 400 Vdc, comes with its own integrated power and control electronics, which communicates with the vehicle by utilizing a common vehicle control system. Other features of Protean’s in-wheel motors include:

  • Mass of only 34 kg (75 lbs.) per motor
  • Integrated friction brake
  • Superior regenerative braking capabilities, which allow up to 85% of the available kinetic energy to be recovered during braking
  • Fits within a conventional 18" road wheel

Protean has developed multiple vehicles with various global OEMs for demonstration in the US, Europe and China.

Protean has been awarded 33 patents for its technology and design, with 101 additional international patent applications pending.

Protean is funded by Oak Investment Partners, GSR Ventures and Jiangsu New Times Holding Group Co., Ltd. Protean Electric has operations in the United States, United Kingdom, China and Hong Kong.

The FAW-Volkswagen Automotive Company (FAW-VW) was founded in 1991 and is a Chinese joint venture between FAW Group Corporation, a Chinese state-owned automotive manufacturing company and Volkswagen Group. On 15 August 2011, FAW-VW celebrated its twentieth anniversary with a milestone of producing its one millionth car.

Resources

  • Alessandro Galeazzi and Gareth Roberts (2013) “Influence of wheel bearing performance on In-wheel motor advanced applications” (EVS 27)

  • Tim Martin and Richard Burke (2013) “Practical Field Weakening Current Vector Control Calculations for PMSM in Vehicle Applications” (EVS 27)

Comments

SJC

Roger,

You described the Tesla, that motor can run above 10,000 RPM with a 9 to 1 reduction and the motor is inductive, no rare earth magnets.

The GM motor in wheel skateboard allowed designers more freedom from the constraints of allowing for the drive train. This provided more room inside with less bulk outside.

Harvey brings up the point of redundancy and fault tolerance. If one of the two wheel motors fails, the driver still has one for propulsion to get off the freeway and to safe parking place.

Roger Pham

@Harvey & SJC,
If one hub motor is to fail suddenly, the car can spin out of control. With two motors mounted side-by-side inside the car body, a limited-slip differential device can couple the two motors together and can permit one motor to power the whole car in case of failure of the other motor. At very low loads, it may be more efficient for one motor to power both wheels, instead of two motors together.

The issue of catastrophic and sudden failure of one hub motor is another disadvantage of the hub motor, unless the two hub motors are electrically connected such that the failure of one motor will deactivate the other motor.

Freddy Torres

The in wheel motor specs are far away from being the best in the market. Take for example an in-wheel Yasa-400, which has a lower weight of only 22 Kg, peak power output of 180 KW, continuous power of 85 KW, peak torque of 400 Nm.
If you want more peak power, the Yasa-750 will tip the scales at only 27 Kg, 200 KW peak power, 75 KW of continuous power, 800 Nm of peak torque.
Since the peak power density of the Yasa-750 is about 7.41 KW/Kg and the peak power density of the Protean in-wheel motor is only 2.21 KW/Kg, it is clear that Protean is very far from having the highest torque and power density of any leading electric propulsion system.
Notice that the Yasa-750 has a peak torque density of 29.63 Nm/Kg while Protean offers 29.41 Nm/Kg.
Yasa motors is clearly the golden standard for in-wheel motors because they are much lighter, much more powerful, and have a slightly higher torque.

Freddy Torres

The Yasa-750 in-wheel motor is vastly superior to Protean is offering. The Yasa-750 is only 27 Kg, 200 KW of peak power, and 800 Nm or torque.
"Protean says that its new production motor provides the highest torque and power density of any leading electric propulsion system"...well, apparently, Protean needs to read www.yasamotors.com and revise their claim.

HarveyD

Driving with one failed hub e-motor would not be worst than flying a 2-engine aircraft with one failed engine.

The average driver should have no problem to reduce speed and take the next exit for repairs.

The electrical control system should have no problem to manage one hub motor failure.

SJC

YASA makes a great motor, they are axial designs. A common failure mode might be the loss of one phase drive. A permanent magnet design like YASA would run at reduced power while the other motor would have full power. The on board computer would compensate. NO Roger, it would NOT spin out of control, that is ridiculous.

Roger Pham

One engine failure on take off or even landing in a twin engine aircraft is a frequent cause of fatality.

The asymmetrical acceleration due to failure of one hub motor will cause the vehicle to drift to one side. If the driver is not sufficiently attentive to correct in time, a crash can happen, or the vehicle can veer to a ditch or a cliff. The stronger the acceleration or deceleration of the hub motors, the less response time for the driver to avert disaster. This is a possible source of liability for the manufacturer. Of course, this can easily be prevented electronically by ensuring that both motors will fail at the same time to avoid asymmetrical thrust.

SJC

That must be why Mercedes and Audi have cars with a motor per wheel, they want to give you more chances of going out of control.

You sound like the doubters that thought front wheel brakes would cause cars to flip over nose first. They were shown to be entirely wrong and you never heard from them again.

Roger Pham

@SJC,
There's such a thing as a VSC (Vehicular Stability Control) system to ensure that asymmetrical traction or thrust will not cause a vehicle to deviate from control.
And then there's such a thing as heavy weight on the wheels which will require expensive suspension system.
It's a matter of physics and not a matter of speculation. The physics of it is very simple and clear.

SJC

Power brakes and steering can go out, but you don't see people crashing. When you have a flat tire, it is usually ONE and you don't see people spinning out of control.

Mercedes and Audi have the SLS and R8e with an inboard motor per wheel because they can get great power and acceleration while keeping unsprung weight low.

One of the main features is vectored thrust and dynamic stability control on ALL four wheels many times per second. The vehicle is safer and handles better.

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Roger Pham

Tire explosion leading to loss of control is a frequent cause of traffic fatality. You've heard of the history of Ford Explorer's tire explosion and deaths before. It's all a matter of risk management and whether it's necessary to take on a certain type of risk.

Of course, low-profile tire and large wheel will help minimize the impact of tire explosion to loss of control. Proper inflation of tires and good tire quality will help.

HarveyD

We switched to the grand father of all radial tires many years ago and we haven't had a single tire problem while driving ever since.

Our new Toyota Camry Hybrid is also equipped with the same 8 low profile high quality radials (4 summer and 4 snow winter tires) and we do not expect any problems for the next 100,000+ Km.

HarveyD

I could have added for the next 100,000+ Km too, on the second set of same summer tyres. The (compulsory) winter tyres last twice as long because they are only used for 3 months/year.

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