Data processing: measuring – calibrating – or testing – Calibration or correction system – Position measurement
Reexamination Certificate
1999-04-06
2001-11-13
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Position measurement
C701S054000, C701S069000, C477S107000, C180S248000
Reexamination Certificate
active
06317698
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electronically shifted four wheel drive system for an automotive vehicle, and more particularly to a system and method for detecting faults in such a four wheel drive system.
BACKGROUND OF THE INVENTION
Four wheel drive systems include Electronically Shifted and mechanically shifted four wheel drive systems. Certain of such electronically controlled systems may be shifted on the fly; meaning thereby there is a microprocessor that controls the shifting. Alternatively, there are Mechanical shift on the fly (MSOF) systems that operate with a manual lever and don't have an electronically controlled unit.
In an electronically controlled system, certain faults are detected and the microprocessor controls the shift device to take appropriate action in the presence of such faults. However, encoder faults are typically not addressed in a robust manner. It would be desirable to provide a system and method which adequately detects encoder faults in a robust manner.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a system and method to detect encoder faults. In a system according to the present invention, a micro-processor is provided to enables accurate, safe, reliable, and fault-tolerant operation. More particularly, the present invention provides observers to diagnose two faults in the transfer case assembly, namely, when the encoder value changes when not warranted (Enc_Changed_Unwarranted) and an error in the encoder channel (Enc_Chnl_Fault).
According to the present invention, a system and method are provided for monitoring the state of a transfer case. A first encoder value is established corresponding to a preselected position of the transfer case. Thereafter it is determined that the shift relays are not energized, and that a first predetermined time period has elapsed since one of the relays was turned off after a shift-attempt. It is further established that a second time period has elapsed since the controller was initialized. A current value of the encoder is compared to the first value. When the current encoder value is not the same as the first value and it is determined that no request was made to change the position of the transfer case a fault flag is set, named Enc_Changed_Unwarranted. If all of the above determinations are not made, the fault flag is not set.
The second fault flag Enc_Chnl_Fault is set with an index based algorithm which manipulates an index in a recursive manner when a relay is on to accomplish a shift. Wrong but valid encoder code received during the shift increments the index while anticipated in-sequence valid value decrements it. The index is increased in a geometrical manner when invalid codes are received in successive cycles during a shift. When the index reaches a preset threshold value during or at the end of a shift, the fault flag Enc_Chnl_Fault is set.
Advantages of the present system include detection of encoder channel faults, including open circuits, shorts, and power failures, while preventing false faults immediately following a shift or immediately after power is turned on to the controller. The present invention can detect an open/short fault in a certain encoder-channel, which would otherwise leave the encoder code as unchanged or may change it to another valid code. As the shift motor rotates, any channel fault will be detected by the present invention. Moreover, the observer responds appropriately to transient faults. When relays are off and the encoder changes due to a fault, the fault flag (Enc_Changed_Unwarranted) is set and as soon as the physical fault in the encoder goes away, the said fault is reset. When the motor is turning during a shift maneuver and occasional wrong encoder codes are received due to noise or intermittent physical faults, the intelligent index-based algorithm does not set the fault flag (Enc_Chnl_Fault) unless the severity warrants it.
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Amatangelo Vincent Frank
Prakash Rajiva
Bui Bryan
Ford Global Technologies Inc.
Ford Global Technologies Inc.
Hoff Marc S.
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