Interrelated power delivery controls – including engine control – Means detecting or ameliorating the effects of malfunction...
Patent
1998-06-12
1999-09-07
Ta, Khoi Q.
Interrelated power delivery controls, including engine control
Means detecting or ameliorating the effects of malfunction...
701 62, F16H 6112
Patent
active
059478675
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a safety system for an automatic transmission in which the actual gear is monitored outside the circuits and when an error conditioned symptom appears it is switched to a replacement gear.
BACKGROUND OF THE INVENTION
In electrohydraulic automatic transmissions, it is generally customary to monitor the methodical operation in order to prevent situations critical to safety. The input signals made available by the sensors, the electromagnetic actuators, the electronic transmission control and, by fed back values, the clutches and brakes that participate in a gearshift, are monitored. In connection with this, EP-PS 0 316 358 discloses a safety system in which the automatic transmission switches to the highest gear in case of an error. The electromagnetic actuators and hydraulics are disposed in a manner such that even in the event of a total electronic system failure, the automatic transmission switches to the fifth gear.
A safety system for an automatic transmission is also known from DE-PS 27 00 548. It prevents a downshift from the highest gear by disengaging an electromagnetic valve when a fault occurs.
The prior art described is disadvantageous in that momentary faults immediately result in a switch to the highest gear or in maintaining the highest gear. In practice this means that, for example, a switch from the first to the fifth gear occurs in the extreme case.
The problem to be solved by the invention is thus to provide a safety system for an automatic transmission, which detects temporary faults and reacts with adequate flexibility.
SUMMARY OF THE INVENTION
The problem on which the invention is based is solved by monitoring the current gear outside the circuits via the measured transmission input and output speeds, wherein a fault detected by the transmission monitoring system present beyond a presettable period of time is interpreted as a symptom, with the safety system thus discontinuing normal operation when a symptom appears. With the discontinuance of the normal operation, the transmission switches from the current gear to a replacement gear. The replacement gear here corresponds to the next higher gear when the symptom appears during first to fourth gears. The replacement gear corresponds to the next lower gear when the symptom appears in fifth gear.
This solution has the advantage that large ratio steps are prevented. Thus, for example, the appearance of a symptom in second gear results in the transmission switching to third gear. An unnecessarily high load on the shafts and couplings is thereby prevented ensuring at the same time that the vehicle is driveable for as long as possible.
Another advantage is that an immediate change to the highest gear, as a result of an error, is prevented since according to the legal regulations this must be indicated as an exhaust relevant error.
In one embodiment of the invention, it is proposed that a symptom counter be provided for each gear. Upon the presence of a symptom, the counter reading is increased by one. If the counter reading exceeds a limit value, an emergency program is activated. This solution offers the advantage that a permanently damaged coupling is detected.
In another development, it is proposed that the emergency gear corresponds to fifth gear when the counter reading exceeds the limit value in one of the first four gears and that the emergency gear corresponds to fourth gear when the counter reading exceeds the limit value in fifth gear. The switchings here are carried out sequentially and are pressure modulated. If the counter reading exceeds the limit value, for example, in second gear, then the change to third gear takes place, followed by the change to fourth gear, and finally the change to fifth gear.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment is shown in the drawings. In the drawings:
FIG. 1 is a system diagram of an automatic transmission;
FIG. 2 is a table of the coupling logic;
FIGS. 3A, 3B, 3C and 3D are program flow charts;
FIG. 4 is a signal phase diagram;
FIG. 5 is a signal phase diagr
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Japanese Abstract (M-1076) Jan. 31. 1991, vol. 15, No. 42 "Number of Revolutions Measuring System Abnormality Detecting Device for Automatic Transmisson".
Deiss Harald
Gierer Georg
Ta Khoi Q.
ZF Friedrichshafen AG
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