The initial work on the ZI drivetrain grew out of the Dutch “EcoDrive” project—a partnership between Van Doorne’s Transmissie (VDT) in Tilburg, the Technische Universiteit Eindhoven (TU/e) and TNO Automotive in Delft.

Zero-inertia drivetrain (ZI). The ZI drivetrain is designed to combine driveability with fuel economy in a Continuously Variable Transmission (CVT). The ZI augments a CVT with a powersplitting planetary gear stage and a compact steel flywheel. The flywheel acts as a “peak-shaver” during speed shifts, delivering power during pedal kick-down and absorbing kinetic energy of the engine at pedal back-out.

Hybrid-electric ZI (E-ZI). The E-ZI implementation electrifies the flywheel in the basic ZI; the flywheel becomes the rotor of a combined motor/generator.

In a conventional application of a motor/generator (MG), in which it is directly connected to the crankshaft, the MG’s inertia accelerates together with the engine. The E-ZI configuration avoids that direct linkage, combining the advantages of electric torque assist with mechanical torques assist from the flywheel.

The E-ZI system supports stop/start functionality, all-electric driving at low speeds, regenerative braking, and the electrification of auxiliary systems. In early testing, the developers delivered fuel savings with a precursor to the E-ZI system of around 18%. (Ecodrive had set a target of 25% fuel savings.)

Impulse Shift Transmission (IST). The IST is based on an automated manual transmission (AMT) with powersplit planetary gearset configured between the engine and the output shaft.

A small flywheel is connected to the planetary gearset. The flywheel prevents torque interruptions in up- or down-shifts, and enables higher overdrive gearing (for improved fuel economy) without penalizing downshift behavior.

Hybrid-Electric IST (E-IST). The E-IST has the same added functions as the E-ZI system, with the flywheel becoming the rotor of a motor/generator.

Flywheel-electric hybrid powertrain (E-fly). The E-fly concept is applicable for hybrids, electric vehicles and fuel-cell vehicles. DTI conceived the electric peak-shaving drivetrain concept for small urban vehicles in which a small motor delivers cruising power and the flywheel delivers the higher-power requests for acceleration and deceleration.

The ease of integration of different concepts developed by Drivetrain Innovations significantly reduces time and costs. The elimination of torque converter for continuously variable transmission (CVT) applications without compromising smooth torque transfers during up shift and down shifts further reduces the need for extra space within the drivetrain.

Drivetrain Innovations has been working on a compact flywheel acting as power supply and energy storage system. DTI has demonstrated its capabilities in some of the concept vehicles. In the coming years, with most of the VMs wanting to invest in hybrid vehicles, the concepts demonstrated by Drivetrain Innovations will go a long way in terms of promoting their commercialization.

—Frost & Sullivan Research Analyst Vijayendra R. Rao

DTI is working closely with European and Asian component suppliers and vehicle manufacturers (VMs) to commercialize its drivetrains.

Resources:

• Component Control for the Zero Intertia Powertrain

• Transmission Design of the Zero Inertia Powertrain

• Optimisation of the Starter Alternator in Zero Inertia configuration

• Performance Analysis of the Impulse Shift CVT