Sealing the Future of in-wheel Motors: Low Friction and Maximum Protection

V-seals and cassette seals offer critical protection from environmental influences and are helping in-wheel motors set new benchmarks.

June 1, 2025

Igor Vukovic and Luca Breusa

In-wheel motor with an integrated sealing system for protection against environmental influences. (Image credit: FREUDENBERG)

In-wheel motors represent a major innovation in the automotive industry, especially in the context of electric vehicles (EVs). In-wheel motors integrate the motor directly into the wheel hub, eliminating the requirement for standard drive components that include cardan shafts, gearboxes and differentials. This integration reduces the complexity of the powertrain and provides several key advantages in terms of performance and sustainability.

Key performance benefits

The essential technical feature of in-wheel motor technology involves wheel-specific torque control accuracy. The independent motor control system enables drivers to make dynamic torque adjustments according to the current driving conditions for improved cornering performance and better high-speed and slippery road stability. The direct motor-to-wheel energy transfer through in-wheel motors creates virtually no energy loss, which enhances vehicle efficiency.

Key sustainability benefits

Cassette seal and V-seal ensure effective protection and minimal friction. (Image credit: FREUDENBERG)

As the automotive industry faces growing demands for sustainable practices, in-wheel motors represent a solution to provide EVs with improved efficiency and performance through direct wheel hub integration of the drive system.

Key challenges

Integrating motors into wheel hubs requires creative solutions to shield these essential components against environmental elements, including water, dirt and dust. Sealing technologies enhance in-wheel motor durability through external contaminant protection and decrease friction while enhancing efficiency.

As in-wheel motors are positioned near the chassis, they can be directly exposed to road dirt, splash water, salty water in winter and the finest dust particles. This environment places extremely high demands on sealing technology, as the motors are heavily impacted without reliable sealing. Any ingress of dirt can result in the corrosion of electrical components, mechanical wear may affect the bearings and moving motor parts, and even the smallest particles can damage the sensitive electronics of the drive system. Electrical short-circuits are also a constant threat if moisture or conductive dirt reaches the components.

Optimized sealing solutions minimize friction and reduce power loss at higher speeds. In this example: cassette seals. (Image credit: FREUDENBERG)

As a result, the sealing systems need to protect against both dust and moisture while being heat-resistant and mechanically durable. The seals need to have long-term durability to survive the motor’s lifecycle without requiring frequent maintenance. The seal dimensions also play a crucial role because they need to fit within the wheel design without blocking its operational capabilities.

The operating environment of in-wheel motors features continuous changes in load intensity. The system needs to function at temperatures above 120°C (248°F) that result from motor output peaks and braking heat. The wheel hub location exposes the seal to continuous mechanical vibrations, together with shocks, because of its direct placement. The seal needs to demonstrate resistance against road salt as well as fuels and oils because these chemicals cause material degradation over time.

Operating cycles also need to be incorporated into the system design. In-wheel motor seals are required to function throughout the wheel’s entire service life by absorbing the wheel’s dynamic movements, including axial displacement from cornering and vertical movements from uneven ground.

V Seal testing data with different materials. (Image credit: FREUDENBERG)

Further, the seals need to endure static and dynamic loads without losing operational capabilities.

Innovations in in-wheel motor sealing technologies

Global sealing suppliers have developed innovative sealing systems designed specifically for the requirements of in-wheel motors. One example is Freudenberg Sealing Technologies’ Cassette Seal system. Its main advantage lies in the speed-dependent sealing effect, as this improves protection when the vehicle is stationary or moving slowly and reduces friction losses at higher speeds. The design is grounded in testing and feedback from the field, which has revealed an inverse relationship between dirt ingress and speed.

The preferred sealing unit for the in-wheel motors consists of either two main components: 1) a dynamic seal component with both radial and axial lips working on a fixed mating contact surface (cassette seal); or 2) an axially acting sealing element (V-seal) that uses the stator as the mating surface. Both configurations enable dynamic adjustment of the sealing effect depending on the wheel’s rotational speed.

V-seals

A V-seal is a specialized seal for in-wheel motors, featuring a unique lip design that effectively blocks dirt while minimizing friction losses. This is especially advantageous as motor rotation speed increases.

Cassette seals

Key properties of V Seals. (Image credit: FREUDENBERG)

A cassette seal integrates a double sealing lip (axial and radial) and the mating contact surface in a closed system, maximizing protection against dirt and water in all operating conditions. The two lips ensure excellent protection even in dynamic conditions where the deformation of the hub creates axial and radial oscillations between the rotor and the stator.

The stainless-steel material of the counterpart, integrated into the cassette seal, guarantees excellent corrosion resistance and an adequate working surface for the sealing lips. In addition, the counterpart creates a sealed environment together with the sealing ring for containing the protective grease. The outer surface of the stator itself constitutes the first solid barrier against impacts from sand, gravel and direct water jets during pressure washing. The design of the axial and radial lip is fully customizable based on the vehicle’s operating conditions, such as speed range, hub deflection and type of contaminant. This fine-tuning allows the customer to achieve the best balance between protection and power loss reduction.

Cassette seals consist of high-quality elastomers and are designed for extreme temperatures and high speeds. The closed design offers secure protection against water and dirt, which increases its reliability in challenging conditions. The special design minimizes friction losses at increasing speeds and lowers energy consumption.

The integrated mating surface ensures precise alignment between the seal material and contact surface, optimizing performance and extending the seal’s service life. The water protection corresponds to protection class IP67 and allows use in damp and soiled environments. The addition of grease during the manufacturing process ensures that the seal is lubricated throughout its lifespan. As a result, the design of the in-wheel motor cassette seal enables the longest service life in its class.

Material and design considerations

Key properties of Cassette Seals. (Image credit: FREUDENBERG)

The material and design of the sealing lips are selected to deliver optimal performance under varying environmental conditions. The sealing lips use high-quality elastomers that provide resistance against both chemical substances and thermal influences. The materials demonstrate outstanding oil and fuel resistance together with excellent resistance to aggressive media while maintaining low permeability. The choice of specific material depends on the application requirements for the targeted area.

The sealing lips are designed with a coordinated geometry that optimizes them for low friction. In cassette seals, additional special grooves ensure that the lubricating film is spread efficiently, and friction is minimized. These cassette seals can also be provided with special lifetime lubrication to further reduce the need for maintenance work. Due to the application of special greases or coatings to prevent the lubricant from drying out or hardening, cassette seals are engineered to operate with little to no maintenance over the system’s lifetime.

The seals also have a protective lip that acts as a barrier against impurities. These protective lips prevent the ingress of dirt, water and other particles into the system, ensuring a longer service life and consistently high performance of the entire assembly. For applications in areas that are particularly susceptible to dirt, cassette seals with additional lips provide effective protection even under extreme conditions.

Key tech specs and advantages

In-wheel motor seals are specially engineered to reduce friction losses at increasing speeds. This is achieved through a special optimization of the sealing lip geometry, ensuring minimal pressure to reduce frictional resistance while maintaining the sealing effect. The result is a significant improvement in system efficiency, leading to greater energy efficiency in vehicles.

Ozone and UV radiation resistance are also essential considerations. The seals are required to maintain their mechanical properties throughout extended environmental influence exposure. The addition of additives to elastomer compounds improves aging resistance while decreasing the chance of material fatigue and embrittlement.

The seals have applications across different vehicle types, including cars and commercial vehicles as well as autonomous shuttles, trailers and two-wheelers. The seals undergo modifications according to application requirements. For example, metal-reinforced carriers improve stability, while integrated sensors can monitor the seal’s position or state of wear. This is of particular interest for modern, networked vehicle platforms, where the importance of predictive maintenance continues to grow.

Future considerations

By combining critical protection against environmental influences with optimized performance, innovative sealing solutions are setting new benchmarks for in-wheel motors. The development of specialized seals like the V-seal and the cassette seal enables automakers to successfully address the technical challenges inherent in integrating these motors, while also improving overall vehicle efficiency. As the seals can be dynamically adapted to varying speeds and environmental situations, the motors are reliably protected and run efficiently under all operating conditions.

Igor Vukovic is head of product engineering, technology and innovation at the Competence Center Fluid Power Automotive at Freudenberg Sealing Technologies. Luca Breusa is testing and innovation manager, lead center SI cassette, at Freudenberg Sealing Technologies.