Method for controlling AMT system including gear neutral sensor signal fault detection and tolerance

A method for controlling an automatic mechanical transmission system (10) for devices having a throttle-controlled engine (14), a transmission having a plurality of gear ratio combinations selectively engageable between a transmission input shaft and a transmission output shaft, said transmission input shaft being operatively connected to said engine by means of a selectably engageable and disengageable coupling providing driving connection between said engine and said input shaft, said automatic mechanical transmission system comprising an information processing unit having means for receiving a plurality of input signals including (1) an input signal indicative of at least one of currently engaged, last engaged and about to be engaged gear ratio of the transmission;

• (2) an input signal indicative of the rotational speed of the transmission input shaft;
• (3) an input signal indicative of the rotational speed of the transmission output shaft, and (4) an input signal indicative of the gear neutral and not gear neutral conditions of said transmission, said gear neutral and not gear neutral condition input signal having a first value indicating the presence of a gear neutral condition and a second value indicating the presence of a not gear neutral condition, said processing unit including means for processing said input signals in accordance with a program and for generating output signals whereby said transmission system is operated in accordance with said program, and means associated with said transmission system effective to actuate said transmission system to effect engagement of said gear ratio combinations in response to said output signals from said processing unit, the method characterized by:
• sensing the presence or absence of faulty input signals indicative of the presence of a transmission gear neutral condition and not gear neutral condition;
• and
• if said input signal indicative of transmission gear neutral condition and not gear neutral condition is determined to be faulty, ignoring said input signal indicative of gear neutral condition and not gear neutral neutral conditions and sensing a gear neutral condition if:
• IS-[GR*OS].noteq..0.
• and sensing a not gear neutral condition if:
• IS-[GR*OS]=.0.
• where:
• IS=a signal indicative of input shaft rotational speed;
• OS=a signal indicative of output shaft rotational speed;
• and
• GR=a signal indicative of:
• the currently engaged gear ratio if a transmission shift is not being executed, the last engaged gear ratio if the transmission is being commanded to shift from engagement into neutral and the about to be engaged gear ratio if the transmission is being commanded to shift from neutral into engagement.