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TM4 and Cummins jointly developing range-extended electric plug-in powertrain for Class 7/8 buses

TM4 and Cummins are jointly developing a plug-in hybrid powertrain for Class 7/8 transit buses that can reduce fuel consumption by at least 50% compared to conventional hybrid buses. The project aims to provide transit authorities with a flexible, more efficient drivetrain and a longer range zero-tailpipe-emission capability for inner-city routes.

The range-extended electric drive system comprises a gen-set (Cummins’ Euro 2019 B4.5 diesel engine coupled with TM4’s LSG130 electric generator); an external 450 kW ultrafast charging infrastructure; a power collector; a 111 kWh onboard Li-ion battery; a TM4 SUMO electric motor directly connected to the differential; a small fuel tank and power electronics.


The Cummins B4.5 is a 4-cylinder, Euro 6-compliant on-road diesel engine that uses a combination of cooled exhaust gas re-circulation (EGR) and variable geometry turbocharging (VGT) on the engine allied to a new aftertreatment system incorporating particulate filtration (DPF) with selective catalytic reduction (SCR).

It has become one of the most widely used engines for lower-carbon diesel electric hybrid buses across the UK and Europe. It is available up to 210ps for trucks and buses, with a strong peak torque of 760 N·m.

TM4 is a leader in electric powertrain development and equipped 5,000 buses in China last year. TM4’s expertise and real-road experience will be instrumental in developing an optimized powertrain for plug-in transit buses.

The TM4 LSG130 generator puts out 135 kW of continuous power at an operating speed of 3400 rpm.

Developed for performance and durability, TM4 SUMO drive systems are optimized for medium- and heavy-duty electric and hybrid vehicles such as 6-18 meter buses, delivery trucks, shuttles, and tow tractors. Direct drive operation reduces powertrain complexity and cost, and yields more than 10% efficiency gains throughout the driving cycle, representing an equivalent gain in battery usage, according to the company.

TM4’s permanent magnet electric motors are based on an external rotor topology, delivering higher power and torque densities as well as increased long-term reliability.

Cummins researchers will optimize the powertrain by selecting the engine with the best architecture to use as an electric commercial vehicle range extender, using the engine to manage the charge level of the all-electric drive battery pack.

Our goal is to offer a system that can achieve 35 km EV range and benefit from the 450 kW fast charging infrastructure to recharge in less than 5 min. The range extender allows for peace of mind and significant flexibility. We are honored to be partnering with Cummins and hope to bring this product to market in the near future.

—Robert Baril, Managing Director of TM4

The range extender will be integrated, using advanced vehicle controls, with the electrified powertrain and other applicable technologies.

The close integration and control of the electrified powertrain with an appropriately selected engine is critically important to developing a plug-in hybrid electric vehicle system. We believe that through the team's efforts we can become a significant player in electrification of commercial vehicles by providing complete systems to benefit our global customers.

—Wayne Eckerle, VP, Cummins Research and Technology

The plug-in hybrid powertrain will be shown for the first time at UITP, taking place in Montréal next week.



Series hybrid works for stop and go.


Drop the diesel and use the electric motor for torque requirements instead then sub in a fuel cell or a small gas burner to maintain cruising speed; Oops, I forgot your guys only make diesels.


Diesel is efficient under steady loads, that is a series hybrid.

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