Engine ignition timing for a clutch engagement control system

#This invention relates to a control for clutch engagement and transmission gear ratio changing. More particularly, it pertains to electronically controlled, hydraulically actuated clutch engagement in a power train that includes a multiple speed ratio transmission or a continuously variable speed ratio transmission and a spark ignition internal combustion engine.

#Objectionable transmission output torque transient vibrations are often produced during a gear ratio change from a previous ratio to a new ratio after a clutch is engaged to produce the new gear ratio and a clutch is disengaged to release the previous gear ratio. The vibrations in the driveline that result from the gear ratio change are in the range from 2 to 10 Hz. Experience has demonstrated that this objectionable vibration can be prevented or reduced if the principal inertial masses, reflected engine inertia, gearset inertia and vehicle inertia, are interconnected with a damping effect that exceeds the relatively small amount of damping that is inherent in the driveline and by the elastic effect of the driveline components that store mechanical energy.

#One of the objectives of this invention is to reduce the transient vibrations in a driveline during upshifts after the oncoming clutch becomes fully engaged. This object is realized by increasing the damping in the powertrain after the clutch is locked up by including a closed feedback loop in the system that controls transmission and engine operation. The feedback strategy employs filtered engine speed and filtered transmission output speed as a basis for advancing or retarding the ignition spark with respect to a reference to increase the damping. The spark timing is altered as a function of the inertia torque.

#FIG. 1 are graphs showing the variation with time of the actual and commanded speed ratios, axle torque and pressure in the oncoming and offgoing clutches of the transmission.

#FIG. 2 is a schematic representation of the automotive driveline whose operation is controlled by the system according to this invention.

#FIG. 3 is a schematic diagram of a gearset and the clutches that control its operation.

#The process of making a gear ratio change in an automotive transmission, in which at least one friction element is actuated to produce each gear ratio, is described first with reference to FIG. 1. There, with reference to an automatic power transmission, an upshift is illustrated and is described below between the first gear ratio, whose associated friction element is depressurized or offgoing, and the second gear ratio, whose associated friction element is pressurized or oncoming. The ratio of the speed of the engine to the speed of the transmission output shaft is the speed ratio. The commanded speed ratio is the ratio of the speeds of these components during an upshift. Throughout the upshift, the road speed of the vehicle is maintained constant. The friction elements whose engagement and disengagement determine the actual operating speed ratio, may be friction clutches, brakes, one-way overrunning clutches or comparable devices. In making the upshift, the capacity to carry torque is transferred from the offgoing clutch to the oncoming clutch as the hydraulic pressure within the clutch cylinders falls and rises, respectively.

#An upshift begins, after a change of speed ratio is commanded, either manually by control of the vehicle operator over the gear selector or automatically according to a shift schedule stored within the control system of the transmission. First, hydraulic pressure in the offgoing clutch cylinder begins to decrease as indicated at point A. Initially the pressure decrease merely permits the excess torque capacity of the clutch, the capacity of the clutch to transmit torque greater than the required torque capacity, to decrease. There is substantially no change in the rotational speed of the driveline as indicated by the upper line of FIG. 1.

#At point B, when the pressure in the cylinder of the offgoing clutch has declined substantially, the offgoing clutch begins to slip and to allow the engine speed to rise slightly. Meanwhile, as the hydraulic pressure in the offgoing clutch continues to decrease, pressurized hydraulic fluid is directed to the oncoming friction element. When the pressure of the oncoming clutch increases initially, as shown in FIG. 1 between A and B, the oncoming clutch piston merely strokes against the return springs, but the oncoming clutch has no torque carrying capacity until its hydraulic pressure increases to the level indicated at D. Thereafter, the oncoming clutch carries torque and gradually assumes at least a portion of the torque formerly carried by the offgoing clutch. As pressure in the offgoing clutch cylinder decreases further past the level indicated at D, pressure rises in the oncoming clutch cylinder to the level at E, where torque is lifted completely from the offgoing clutch and is carried entirely by the oncoming clutch.