Permanent Magnetic Motors make Electric Vehicles Viable

The popularity of electric vehicles is rising in most key markets around the world, as environmentally-conscious consumers, prompted by increasing amounts of legislation, buy-in to the need for less polluting transport options in our towns and cities.

This trend is also being driven by rapid improvements in the performance of the vehicles themselves, with increased range and lower battery costs persuading many consumers to make the switch from conventional powertrains. According to a report by McKinsey, an estimated 120 million electric vehicles are expected to be on the roads in Europe, USA, and China by 2030, with a more aggressive-case scenario could see that double. That level of uptake would represent a green transformation of the vehicle fleet, supporting global efforts to reduce harmful vehicle emissions at the point of source.

The challenge, then, is for engineers to continue to improve the performance of electric vehicles, primarily through a process of incremental refinements that add up over time. One crucial component being looked at consistently is the electric motor – the means by which power is transferred from the traction battery pack to the wheels. These components are expected to offer high torque and power density, along with other capabilities such as high reliability and low noise.

Traditionally, induction motors have proved a popular solution for electric vehicles. But more recently there has been a trend towards the use of permanent magnet motors – where the magnets are positioned within the rotor core creating a permanent magnetic field that does not require any additional current to generate the field. Permanent magnet motors are widely seen as offering higher levels of efficiency than induction motors, which has resulted in them being adopted on some high-profile vehicles such as the 2019 Tesla 2019 Model S and Model X.

Indeed, permanent magnet motors have been the subject of intense research and development effort at Parker for more than a decade. This activity is represented by the Global Vehicle Motor (GVM), a range that was created initially for both on and off-road vehicles, engineered for traction, electro-hydraulic pumps, and auxiliary applications. The torque density and speed capabilities of the motor, combined with a voltage matched inverter, provide the speed and torque required to achieve breakthrough performance in a variety of vehicle platforms.

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Figure 2: Small Electric vehicle

To look at the GVM in a little more detail, for a 100 kg weight, performance characteristics include continuous power up to 170 kW, peak torque up to 710 Nm, rotational speed up to 9800 rpm and low and high voltage options from 24 VDC to 800 VDC. The use of rare earth magnets, meanwhile, allows for high-temperature operation.

GVM is a rugged design, too, being shock-proof, vibration-proof, and salt spray resistant, and coming IP6K9K rated when assembled on a gearbox or pump. Moreover, it uses a new patent-pending advanced cooling system that has minimal impact on the size and weight of the motor. Those technical attributes have seen the GVM used in an increasingly wide variety of vehicle applications including construction vehicles, refuse trucks, city buses, street sweepers, motorcycles and scooters, light commercial vehicles and even watercraft.

When it comes to electric vehicles specifically, though, the GVM has some particularly useful characteristics that make it ideal for use on small city vehicles. The range comes in a ‘kit’ form which includes frameless options; designated as the Global Vehicle Kit (GVK) range which includes only the active parts of the GVM motor – effectively omitting the mechanical parts, with the rotor and stator built into the machine assembly. This can have huge appeal for engineers working on small city car programmes, who are often seeking greater design flexibility in ways that allow them to eliminate parts that would add weight and size.

The frameless approach offers many advantages over traditional technologies, thanks to a more seamless mechanical and electrical adaptation to the application requirements. This can lead to a highly efficient and dynamic design. It can, for instance, offer some real benefits in terms of compact sizing, allowing integration in the same space with the gearbox. There are also weight and complexity advantages that are achieved by eliminating the frame, too.

Once the OEM chooses the specific solution, the more integrated nature of the design means it is easier to mount the motor. Also, the close integration of frameless designs can be more stable and better balanced than traditional motors, and the reduction in the number of components used means they can deliver lower through-life costs.

Crucially, Parker works closely with customers to ensure that the right PMAC motor is selected for a specific application’s needs. This collaborative approach involves taking an informed view from the outset on how the main elements – the stator and rotor – can be seamlessly integrated into the broader vehicle platform. This partnership ensures that complexity is reduced, and that maximum performance benefit is derived.

But what does this all mean for the end-user?

Well, the more seamless integration possible with GVK frameless PMAC motors delivers benefits in several ways. In addition to a more flexible and efficient design, they offer important cost savings for the customer through better integration plus inherent advantages, just like the GVM, that include reduced fuel consumption, reduced emissions, quieter operation and a downsizing of the power system.

Overall, the use of frameless motors such as Parker’s GVK can result in a more refined, better-performing vehicle that is closely aligned to the specific needs of the greener vehicles of tomorrow.

Looking forward, Parker believes that PMAC motors will continue to find more extensive application for traction in electric vehicles as the market continues to grow and model choice proliferates.

Parker Hannifin