This invention relates to electric control of the feed pressure of a hydraulic receiver, particularly for an input clutch in first gear of an automatic transmission for a motor vehicle.
For control of this type of clutch, systems called declutching at stop with electronic control are known, such as described in U.S. Pat. No. 4,633,985, which make it possible to eliminate, on a vehicle equipped with an automatic transmission, the spontaneous tendency to "creep" from stop, when driving circumstances cause this tendency to be considered undesirable.
The main difficulty encountered in developing such systems appears during restarting, when the driver again presses on the accelerator and opens, in an essentially variable manner, the throttle (Gasoline engine) or Diesel fuel metering device (Diesel engine); actually, it is very difficult to find adjustments that are satisfactory from the viewpoint of comfort in starting both for a start with a light depression of the throttle and for a full throttle start. The drawbacks are reflected by a jerk at acceleration that is unacceptable considering the standards of comfort demanded of modern automatic transmissions.
These deficiencies are explained by the fact that the stop declutching systems known so far are activated by the simultaneous occurrence of preset conditions particularly in the speed of the vehicle, the speed of the engine, the output speed of the converter and the position of the fuel feed metering element of the engine; in particular, for this latter, most often the condition EQU .alpha.c=.alpha.c at idle
is imposed.
It is precisely this latter condition that is insufficient to assure under all circumstances the comfort demanded at restarting. Actually, this single condition on .alpha.c does not take into account:
The advantage and pleasure in being able to make maneuvers at idle, precisely by using the phenomenon of "creeping" peculiar to automatic transmissions; actually, to cause declutching to cease at stop, .alpha.c must be greater than .alpha.c idle, which comes down to pressing notably on the accelerator;
The inevitable response time in filling the cylinder of the input clutch, which although kept in lined-up position, is not able to transmit without some delay, even though minimal, the full engine torque during full throttle start; by its very nature, the .alpha.c measurement does not permit any anticipation of the arrival of the torque, an anticipation that would make it possible to reduce the response time of the input clutch.