Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
1999-10-14
2001-02-06
Marmor, Charles A (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C477S162000
Reexamination Certificate
active
06183393
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for reducing jerking during gear shifting of an automatic transmission driven by an internal combustion engine.
As disclosed in “Funktionsbeschreibung Automatikgetriebe, 5 HP 19 FL” of ZF Getriebe GmbH Saarbrucken, issued in August 1995, an automatic transmission with a selector lever having a forward drive (D) and reverse drive (R) positions, and parking (P) and neutral (N) positions. In the R, N and D positions (first gear) a first clutch is closed. By moving from position D to N a second clutch is opened and by moving from the position R to N a third clutch is opened. In an automatic transmission of this kind a problem can arise in the practice: when gear shifting, that is, in the transition from the position D to N or from R to N, respectively the second or third clutch is opened. The shifting quality when changing gears is determined by the manner in which it is possible to smoothly carry out the torque reduction. Decisive for this are, on one hand, design of the vehicle and, on the other, the duration of pressure reduction of the clutch being disengaged. However, the requirement of a good shifting quality is opposed to the requirement of adequate safety and durability criteria. These determine that under all conditions, such as low temperatures, the clutch to be disengaged must be drained with certainty. If this is not ensured, then when the clutch opens and the accelerator pedal is simultaneously actuated, there can result a destruction of the clutch. Since the safety and durability criteria must be ranked above the comfort demands, jolts occurring when gear shifting have hitherto been accepted.
The problem on which the invention is based is now to provide for the above described automatic transmission that both requirements, namely, comfort and safety, be satisfied.
SUMMARY OF THE INVENTION
According to the invention, the solution consists in that upon detection of a gear shift condition the pressure level of the first clutch be reduced from a first to a second pressure level, the second pressure level being above the slip limit so that the first clutch remains closed.
In a development of this, it is proposed that upon detection of the position N and opening of the second or third clutch, the first clutch be opened for a presettable time. After lapse of the time step, the pressure level of the first clutch is again raised, via a ramp function, to the second pressure level so that the clutch is again closed.
A first advantage of the solution, according to the invention and the development thereof, consists in that as result of the flat pressure gradient of the first clutch to be disengaged, the transmission input torque is smoothly reduced before the second or third clutch is regularly disengaged, coming from a high pressure level and becomes drained. A second advantage consists in that said function can only be implemented by a software change. Changes in the hydraulic system of the transmission hardware are thus unnecessary.
In a development of the invention, it is proposed that the gear shift condition be detected when: the temperature of the hydraulic fluid is higher than a limit value and the transmission output rotational speed and a performance wish and motor rotational speed presettable by the driver are each below a limit value. This development offers the advantage that the different chassis conditions are adequately taken into account.
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ZF Getriebe GmbH Saarbrücken, “Funktionsbeschreibung Automatikgetriebe, 5 HP 19 FL”, Aug. 1995, pp. 23-29.
Davis and Bujold
Ho Ha
Marmor Charles A
ZF Friedrichshafen AG
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