Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Patent
1999-05-06
2000-12-05
Zanelli, Michael J.
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
477 34, 477 70, F16H 6106, F16H 6108
Patent
active
061578835
DESCRIPTION:
BRIEF SUMMARY
This invention concerns a method for increasing the spontaneity of an electrohydraulically controlled automatic transmission in which a gearshift from a first reduction step to a second reduction step in a downshift is effected by a first clutch opening and a second clutch closing.
BACKGROUND OF THE INVENTION
In automatic transmissions, gearshifts are usually overlapping gearshifts, that is, a first clutch opens and a second clutch closes. Thus, U.S. Pat. No. 5,079,970, for example, proposes an overlapping gearshift for a downshift wherein, at the beginning of the shift, the pressure level applied to the first clutch is reduced to a lower pressure level according to a ramp function. This is followed by a time function during which the transmission input speed increases. The pressure curve of the second engaging clutch, consists of rapid filling, filling equalization and a load take-up phase. Downshifts are usually produced when an presettable accelerator pedal value exceeds a downshift characteristic line. Together with downshifts produced by means of the accelerator pedal, the driver also has the possibility of producing manual downshifts whenever desired. DE-OS 43 11 886, for example, shows a device by which with the aid of a selector lever the driver can produce gearshifts with a manual gate or shifting rocker on a steering wheel. For manually produced downshifts, for example, there arises, in practice, a problem of long reaction times, that is, the time interval, from the manual demanded downshift, until a noticeable reaction of the automatic transmission appears. Long reaction times result from the idle times of the signals controlling the hydraulic system, blocking times between two consecutive gearshifts and the time needed for the disengagement of the first clutch or filling of the second clutch. The long reaction times are felt as unpleasant by the driver.
The invention is based on the problem of improving the spontaneity of the automatic transmission, specially in a downshift and a double shift included therein.
SUMMARY OF THE INVENTION
According to the invention, the problem is solved by reducing, with the issuance of the shift command, the pressure level of the first clutch from a first pressure level to a second pressure level and maintaining the second pressure level during a hold time, this being a function of a rotational speed differential of a transmission input speed and the temperature of the hydraulic fluid. With the termination of the hold time, the pressure level of the first clutch is reduced to a third pressure level for a recovery time. This third pressure level determines the recovery time curve of the transmission as the pressure level of the first clutch is reduced to zero. The solution, according to the invention, offers the advantage of a variable hold time. The reaction time is determined by said hold time. Preferably, the hold time is patterned in such a manner that a small speed jump of the transmission input speed a long hold time is provided and in a large jump of the transmission input speed a very short hold time is spent.
Preferably, the speed jump of the transmission input speed is calculated from the transmission input speed at the beginning of the gearshift in the first reduction step and the value of the transmission input speed at the synchronization point of the second reduction step.
For applying the method to sequentially performed double shifts, it is further proposed, according to the invention, that in double shifts comprising a first shift and a second shift, the second shift corresponds to a downshift, the change for the second shift as described above.
In a development of this, it is proposed that in a double shift in which the first shift corresponds to an upshift from a first to a second reduction step, a time step be started with disengagement of the first clutch. Said time step extending up to a maximum time wherein a reduction time is associated with each value of the time step. The reduction time in that case determines a rapid filling time o
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Popp Christian
Rosi Hansjorg
Tenbrock Friedrich
Gibson Eric M.
Zanelli Michael J.
ZF Friedrichshafen AG
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