Throttle-less Operation

View a series of in-depth pages on throttle-less operation in SI engines. These pages look at how a variable lift and duration VVA system can be used to significantly improve engine fuel economy.

Part 1: part load introduction

This section gives a brief introduction to engine operation at part load. It shows, using idealised pressure-volume diagrams, how significant improvements in fuel economy can be made by implementing a throttleless load control strategy.
Introduction to part load operation

Part 2: intake valve closing strategies

throttleless operation, using valve-head load control can be achieved by either early or late intake valve closing. This section describes and compares both these methods for improving part load fuel economy.
Intake valve closing concepts

Part 3: other part load strategies

There are of course many other ways of improving engine fuel economy. Three other popular methods are described within this section. These are cylinder deactivation, exhaust gas re-circulation (EGR) and gasoline direct injection (GDI). There is also discussion on whether these strategies can be used for throttleless operation.
Other part load strategies.

Part 4: valve motion considerations for early intake valve closing

This section compares ideal and realistic valve motions for throttleless load control, showing the reductions in pumping work that are feasible with the use of a variable lift and duration VVA system.
Valve motion considerations

Part 5: performance benefits

This section summarises the typical performance benefits that can be expected from throttleless operation. There is also discussion of the potential for improving engine output (power and torque) via use of a variable lift system.
Potential performance benefits