Third-generation EV powertrains need to achieve reduced weight and improved efficiency, but engineers also need to have clear focus on cooling options, states Neil Heslington, Managing Director of Zytek Automotive, which develops electric drive systems.
Zytek recently announced that it is developing new lightweight battery-electric powertrains, including an air-cooled solution that the company claims is 45% lighter than current EV powertrains and a water-cooled one that is about 30% lighter.
“Cooling options must be a particular development area,” notes Heslington. “The marriage of convenience that marks out most present EV technologies cannot continue.”
The new Zytek powertrain is expected eventually to form part of the Gordon Murray Design (GMD) model lineup. The T27 electric vehicle concept is based on the recently revealed T25 platform, with a 25-kW version of the air-cooled unit contributing to the vehicle’s compact dimensions and low weight.
The powertrain issue and the need to reduce cost and weight of the battery remain central to a wide span of EV development challenges that include vehicle range, cost, cabin heating and cooling, battery pack size, charging infrastructure, legal issues, and driver education.
It is vital that all disciplines work together to get weight out of EVs, Heslington asserted.
Packaging of any new powertrain is important. Zytek is aiming at an overall width between motor/gearbox and end faces of 300 mm (11.8 in) for A- to C-segment cars or light commercial vehicles. An equivalent transverse IC engine/gearbox is now about 950 mm (37.4 in).
Heslington sees the immediate future for EV series production as delivering powertrains that are liquid-cooled, their electric machines revving to a maximum 14,000 rpm and driving through a single-ratio gearbox. Their battery chargers will be integrated within the inverter. Efficiency gains will be achieved via areas including motor design and careful planning of components to keep cable runs to a minimum length.
Next would be a powertrain revving to some 10,300 rpm to increase efficiency. A gearbox would have ratios of around 3:1 to 6.5:1 to keep the motor within its most efficient speed range without compromising pull-away or top speed. Modularity would facilitate linking two powertrains to simply double power and torque.
Heslington stressed the need for parallel design and integration of minor and major subsystems. The company has revealed that it is working with Vocis on transmission solutions.
The companies will introduce a motor and gearbox as a single system to reduce weight and packaging. Under test now, it is only 135 mm (5.3 in) wide across the gearbox and will be part of the T27 power unit.
“The compact dimensions of the new air-cooled drivetrain make mechanical integration with an EV much simpler,” adds Heslington. “The main connections required are high voltage to the traction battery and low voltage for electrical interface with the vehicle.”
Zytek has developed an EV control module that interfaces with all standard vehicle systems such as ABS and ESP. The module provides required diagnostic information together with its own range of diagnostic codes.
Homologation is still a continuing issue for EVs and is complex, with requirements needing to meet SAE standards, EU legislation, low-voltage directives, and manufacturers’ internal requirements.
“But it is the driver that is the biggest variable in all this,” says Heslington. “Range of EVs is far more dependent on driving style than with IC vehicles. The driver has to be educated and informed. The aim must be not to impair the driving experience but limit discharge and encourage regenerative braking.”