Controlling a servo controlled motor vehicle gearbox
System for controlling a servo-controlled gearbox, configured so as to use gear-shifting strategies similar to those used by a human driver so as to improve the driving sensation experienced by the driver. The control system uses a plurality of sensors (SENS) disposed in the vehicle for detecting the various operative conditions and a system of rules (a rule-based system) for implementing the strategies provided for.
The control strategies of the system have to adapt to the operative conditions of the vehicle in order to maintain the driving sensation required by the user.In particular, the servo-controlled gearbox must react to the driver’s commands correctly, even during emergency operations, during sports driving and on particularly demanding road sections such as mountain routes.
Automatic and servo-controlled gearboxes according to the prior art in fact have the disadvantage of using different strategies from those which would be adopted by a human driver. This means that the driver of a motor-vehicle having such an automatic gearbox feels uneasy when he is driving and is unsure of the reactions of the gearbox so that driving safety is reduced. The driver’s psychological uneasiness may also reduce has concentration during driving.
A classical example of the problems which may be encountered with the use of conventional automatic gearboxes is the following. Faced with a descent, the driver usually lifts his foot from the accelerator in order to compensate for the effect of gravity which tends to cause the vehicle to accelerate. The automatic gearbox control often interprets this action as an intention by the driver to proceed more economically, that is, as a request for less power/acceleration, and hence engages a higher gear than the previous one.
The driver thus loses the engine braking effect on which he was counting to limit the vehicle speed. He is therefore forced to brake or to force the automatic gearbox manually into a lower ratio if he does not wish to use the brakes (or if they are not to be overheated). On a stretch of mountain road, however, this means that driving becomes disagreeable since it requires the driver to override the control system of the automatic gearbox (substituting himself for it) by using it as a manual gear-shift.
The system comprises a microprocessor control unit, a plurality of sensors coupled to said control unit for providing signals representative of physical entities relating to the operation of the vehicle, and actuators which are driven by the control unit for controlling the operation of the gearbox. The system is adapted to implement different gearbox control strategies in dependence on the driving conditions detected. Speed selection means allow the user to select a desired vehicle ground speed and the system automatically selects the specific transmission gear and engine speed required to achieve the desired ground speed.
These servo-controlled gearboxes can thus perform all of the operations necessary for a gear shift without intervention by the driver. Naturally, however, a control unit, typically an electronic control unit ECU controlling the actuators ATFR, ATSE, ATIN, is required. There are two different possible control modes for a servo-controlled gearbox. In a first, semi-automatic mode, the gearbox C operates upon the driver’s command, that is, it executes a gear shift only when required to by the driver.
In this case, the control strategies are concerned solely with controlling the various operations relating to the gear shift. In a second mode, the gearbox operates like an automatic gearbox. In this case, the control strategies are more complex and also decide how and when to execute gear shifts, whilst the driver no longer communicates any commands to the gearbox.
These are the output signals of the sensors SENS used to measure the speed of rotation of the engine shaft and of the primary and secondary shafts of the gearbox. These quantities will be defined below for simplicity of notation as engine revolutions GMCT, gearbox input revolutions GING, and gearbox output revolutions GUSC. The value of GUSC is proportional to the speed V of the vehicle and is therefore used to derive this latter datum.
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