Strong flex: ZF launches EcoFlex, a low-maintenance coupling for electric rail drivelines

As rail operators expand electrified services and increase vehicle utilization, fleet availability and lifecycle costs have become an increasingly important measure. Around 90 percent of Germany's rail traffic is already electrically powered, while heavily used sections of the rail network continue to experience growing usage. At the same time, global metropolitan rail systems are expected to transport vast numbers of passengers every day. In Rome, for example, the metro network carries more than one million passengers daily. This generates a lot of strain on the driveline, which directly influences everything downstream from the vehicle.

For operators, every unplanned workshop visit reduces fleet availability, so repairs and overhauls need to be fast, easy and cost-efficient.

For manufacturers, in turn, maintenance requirements influence lifetime operating costs and vehicle competitiveness. For passengers, delayed maintenance affects reliability, ride comfort and punctuality.

To address these requirements, ZF has developed EcoFlex, a new fiber composite coupling for EMUs that combines low-maintenance operation, integrated damping and inherent electrical insulation in a single design.

EcoFlex: small component, big impact

At the heart of EcoFlex is a flexible composite disc coupling that uses circumferentially arranged fiber packages embedded within an elastomer element. These fiber bundles transmit torque while simultaneously compensating for dynamic movement between motor and gearbox. The elastomer protects the fibers and supports rail-specific fire and smoke requirements. At the same time, the insulating traits of the elastomer-fiber disc result in an electrical resistance exceeding 1,000 MΩ. This eliminates the need for additional insulation measures commonly required in conventional coupling systems. In its current stage, EcoFlex can transmit up to 2,100 Nm and sustain motor speeds of up to 6,000 rpm. ZF is planning to develop additional coupling sizes with corresponding performance.

Unlike lubricated curved-tooth gear couplings, EcoFlex requires no lubrication and is designed to minimize wear-related service work. Routine visual inspections remain part of operation, while replacement of the flexible disc assembly is planned after approximately eight years, depending on the validated duty cycle and application.

Designed for lower lifecycle costs and more ride comfort

The coupling's design also helps operators reduce lifecycle costs by combining a low-maintenance architecture with a reduced number of individual components.

In addition to transmitting torque, EcoFlex contributes to driveline protection through integrated damping characteristics. The interaction of the fiber packages, elastomer material and integrated slipping bush helps to limit torque peaks and dynamic load changes. This reduces stress on driveline components, while also benefiting overall ride comfort.

Flexible integration for both new and retrofit builds

EcoFlex has been designed for broad applicability across EMUs and metro vehicles. The coupling can be adapted to specific customer requirements, including shaft interfaces and installation dimensions, enabling straightforward integration into new vehicle platforms as well as existing fleets. This flexibility also supports retrofit projects where operators seek to replace conventional couplings with a modern, low-maintenance solution.

"EcoFlex demonstrates how we continue to expand the ZF Rail portfolio with solutions that address concrete customer requirements. By combining low-maintenance operation, electrical insulation and integrated damping in a single coupling design, we help operators improve reliability and comfort while reducing lifecycle costs and give manufacturers greater integration flexibility," states Hans-Peter Niedermeier, Head of Product Development for Rail Drive Systems at ZF.

Next steps toward operational deployment

Following successful validation testing, ZF is preparing the next stage of the EcoFlex development program. The company is currently in talks with a vehicle manufacturer to conduct joint metro field tests. The trials are intended to evaluate performance under real-world operating conditions and provide additional insights for future series applications. The company is also in pre-development of additional coupling sizes for a broader range of vehicles.

Premiere at InnoTrans 2026

ZF will unveil EcoFlex during its ZF InnoForum event, held on the first day of InnoTrans (September 22 at 3 p.m.). The new technology is a main exhibit at ZF’s booth 580 in hall 20, where the company will also highlight a portfolio spanning driveline technologies, chassis components, digital condition monitoring solutions and global service offerings.