Abstract
Automotive driveability includes the vehicle acceleration response in the fore/aft direction to driver inputs such as throttle and gear change. It is becoming increasingly important to improve driveability refinement to meet customer expectations.
To deliver good driveability it is necessary to reduce hesitations and oscillations in the vehicle fore-aft dynamic response allowing the vehicle to start, pullaway, accelerate, decelerate and drive smoothly; this makes the vehicle feel more stable and refined. The vehicle fore/aft dynamic response is significantly influenced by the first torsional mode of the driveline. This paper will concentrate on the development of the vehicle response to a tip-in, that is, moving the throttle from closed to open, for a petrol Ford Focus.
To maintain competitiveness there is a requirement for vehicles to be developed quickly with a reduced number of prototypes. It was essential that the Ford Focus engineering specifications for driveability be determined prior to prototype vehicles being available. Therefore the vehicle, engine and EMS (Engine Management System) were modeled using CAE (Computer Aided Engineering). A cross attribute team that specialised in system modelling and design was created to improve the vehicle response to a throttle transient. The team looked at such areas as driveline hardware, timing of transient spark, transient fueling effects, EMS processor timing and interaction effects, and their effect on throttle transient robustness for different manoeuvres.