Abstract
The drive off is defined as the maneuver in which the engine and the driveline are mechanically coupled, through the operation of the clutch, in order to transmit motion to the vehicle.
When the internal combustion engine (ICE) is used in automotive applications, the intrinsic inability to generate torque at low operating speed could create bad drivability feelings to the driver, due to engine stall occurrences, engagement shock phenomena or RPM fall.
Moreover, in the last years the automotive engineering has moved toward downsized engine to improve the fuel economy, to reduce the emission and to reduce the production costs. Despite the use of the over-boost technology, if an engine is downsized, the power output at low engine speed is reduced: worsening the drive off manoeuvre that is one of the most important for the customer satisfaction.
In manual transmission automobiles, drive off is much more critical due to the inability of the engine control unit (ECU) to manage the actuation of the clutch.
Other aspects that negatively affect the drive off maneuver are:
- unavoidable dispersion between the pedal position and the actual position of the clutch plates
- backlash of the accelerator pedal
- increase of vehicle weight and of the road load; i.e. uphill road
- clutch wear
The aim of the presented work is to solve the customers complaints due to uncomfortable drive off manoeuvres. The number of this complaints is rising on manual transmission vehicles equipped with downsized engines.
In this article an innovative control algorithm is presented, that is able to cope with all the difficulties presented above, in order to manage the vehicle drive off manoeuvre (Drive off Management Algorithm, DoMA). The main goal of DoMA is to reduce the occurrences of engine stall and to avoid the engagement shock phenomena during the drive off maneuvers. To achieve its goals, DoMA recognizes the start of a drive off maneuver, it raises the engine speed in order to increase the available engine torque before coupling phase, it increases the authority of idle speed control to manage the growing total inertia during coupling phase and, at the end, it smoothly reduces its action to avoid the engagement shock.
DoMA has been firstly tested in simulation environment (MATLAB/Simulink) on a simplified powertrain model; it has then been tested on vehicle using Rapid Control Prototyping environment (RCP). In both cases DoMA has shown a good performance, confirmed by objective measurements and drivers evaluations.
In the second chapter the drive off improvement reasons are described; during the chapter three the vehicle equipment is presented; in the fourth chapter, DoMA algorithm is described. In the chapter five the experimental activity and its results are discussed. In the end the conclusion are drawn.
KEYWORDS: Drive off, engine stalls, shock phenomena, idle speed.