| 摘要 |
An improved automobile transfer case system (10) and electronic control circuit (16) therefor utilizes a reset circuit (70), a microprocessor (72), and an output stage (74) to operate an electronically controlled coupling (38,58) that is used to switch between drive modes in the transfer case (14) of a full or part-time four wheel drive vehicle. The microprocessor (72) is connected to a source of operating power that is available even when the vehicle ignition is switched off. The microprocessor (72) runs in two modes, a low power standby mode and an operating mode. The microprocessor enters the standby mode when vehicle ignition is switched off and it has finished any tasks that were in progress when the ignition was turned off. The reset circuit (70) responds to the ignition being switched on to provide a hardware reset of the microprocessor (72) that wakes it up from its standby mode and places it into the operating mode. Once in the operating mode, the microprocessor (72) determines the current driving mode via a position encoder (60), as well as the desired mode via a switch (68), and thereafter makes any desired or needed shifts between driving modes. The reset circuit (70) includes a combinational logic circuit (78) and an RC circuit (80) which provides a time constant that determines the width of the reset pulse provided to the microprocessor (72). The reset circuit (70) receives a signal indicative of which mode the microprocessor (72) is in so that the microprocessor will not be reset if it is already in the operating mode.
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