Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Patent
1996-08-16
1998-03-03
Marmor, Charles A.
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
477120, 477149, 477155, F16H 6108
Patent
active
057229139
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In automatic transmissions a transition from a first lower reduction step to a second higher reduction step (downshift) occurs when a first clutch disengages and a second clutch engages. The start of the pressure increase in the second clutch and the pressure achieved at the end of the gearshift are selected here so that the second clutch reliably takes up the torque to be transmitted at the synchronization point. The synchronization point is calculated by multiplying the actual transmission output speed by the reduction ratio of the second reduction step. A displacement of the take-up point can result from disturbance variables. Disturbance variables are, for example: tolerances of mechanical parts, temperature influence of the pressure medium, scattering of the friction value of the clutch discs and change of the friction value during the useful life of the transmission. The disturbance variables act upon both clutches. A displacement of the take-up point produces a clear impairment of the ease in gearshifting. Along with the disturbance variables related to the transmission, the power output of the internal combustion engine also influences the ease in gearshifting. The power output of identical internal combustion engines is known to disperse within the series.
DE-OS 40 23 365 has disclosed a process for gearshifting an automatic multi-step change transmission. The process relates to a downshift. After disengagement of a first clutch, a second clutch is engaged after a time step has elapsed. An impairment in gearshift ease is detected by evaluating torque-dependent parameters such as misalignment of the engine and transmission unit or speed change of the transmission output speed. If said parameters exceed a limit value, the time step is adapted.
SUMMARY OF THE INVENTION
The problem on which the invention is based is to ensure a steady ease in gearshifting during downshifts.
According to the invention the solution of the problem involves two possibilities: in a first possible solution it is assumed that a transmission input speed runs past the synchronization point. According to the invention, transmission input speed is to be understood as the speed of the turbine wheel of a hydrodynamic converter. For the above mentioned case it is proposed that a speed value, at which the pressure begins to increase in the second clutch, be assigned from a characteristic curve to a synchronizer speed value, and the characteristic curve be adapted when the transmission input speed is higher than the synchronizer speed value. In development of this, it is proposed that the characteristic curve be adapted so that the assigned speed value after the adaptation is greater than the assigned speed value prior to the adaptation for the same synchronizer speed value. Another development provides that at a first moment, a first gradient of the transmission input speed and at a second moment, a second gradient of the transmission input speed be cyclically determined, and upon a change of signs of the gradients from plus to minus, the input speed value at the second moment be set as a maximum.
In a second possible solution it is proposed that a speed value, at which begins the pressure increase of the second clutch, be assigned from a characteristic curve, to a synchronizer speed value, that at a first moment, a first gradient and at a second moment, a second gradient of the transmission input speed be determined, that a difference be calculated of the second gradient minus the first gradient, that the characteristic curve be adapted when the difference exceeds a limit value and that the transmission input speed at the second moment be set as a minimum. In development of this, it is proposed that the characteristic curve be adapted so that the assigned speed value after the adaptation is less than the assigned speed value prior to the adaptation for the same synchronizer speed. In this solution it is assumed that the transmission input speed at the take-up point is lower than the calculated synchr
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Estremsky Sherry Lynn
Marmor Charles A.
ZF Friedrichshafen AG
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