IdleStop and Go: a way to improve fuel economy

Abstract

This paper proposes a mechanical solution to save fuel by shutting down an internal combustion engine whenever it is unnecessary for propulsion, e.g., when a vehicle is waiting for traffic lights. The engine and vehicle are restarted using the energy that is stored in a flywheel. Two additional clutches are needed to enable appropriate power flow from the flywheel to the engine and vehicle. This complicates the powertrain dynamics in that the number of degrees of freedom changes due to clutch operations. Therefore, a hybrid control strategy, which is treated as a top-level controller, is introduced to deal with this finite-state mechanical system. At the lower level, the engine and clutches are controlled in a coordinated manner such that the vehicle is launched according to the driver's demands. Using a comprehensive powertrain simulation package, the proposed controller is evaluated numerically.

Keywords:

• IdleStop and Go
• Hybrid control
• Fuel economy
• Powertrain control

Notes

^†This implies a transmission efficiency of around 70%, which is typical for an automatic transmission on a city cycle.

^‡The results depend on the specific vehicle being considered and the speed and load conditions imposed by the driving cycle.

^†The mentioned torque converter cannot transmit any power when it coasts down.

^†The specific torque converter is not able to transfer substantial negative torque.

^†A brief version for Stop–Go, which is another name for SG.

^†These two torques are the same when the clutch is slipping and different when the clutch is engaged.

^†The above control law requires accurate information about road load T _rl if has to be controlled precisely. More advanced feedback control laws may be necessary to overcome the road load disturbance.