Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
1999-10-12
2001-05-22
Camby, Richard M. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S035000
Reexamination Certificate
active
06236919
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
BACKGROUND OF THE INVENTION
The present invention relates to electronic circuits for use in automobiles and in particular, to an apparatus and method for processing automotive electronic signals during periods of low system voltage.
In recent years, the number of electronic signals in an automobile has increased dramatically. This large number of signals is managed through the use of signal integration hubs having connectors for receiving conductors from a wide variety of sensors and actuators, and a microprocessor for processing such signals. The automobile instrument cluster is one site used as a signal integration hub because a large number of actuators, such as electronic gauges, lamps and chimes that are found there and because it is in a protected location in the instrument panel near the engine compartment. Other locations for signal integration hub locations are also possible.
While starting the automobile engine or at other times of high current demand, the standard system voltage of approximately twelve volts may drop. A low system voltage may affect digital input circuits and the output of automotive sensors that rely on this voltage as an implicit reference. In these input circuits and sensors as the system voltage drops, the state of the digital input or the output from the sensor may change. System voltage induced changes may be interpreted by a microcontroller at the signal integration hub as a change of state in the sensed quantity and may result in the erroneous control of actuators.
The electronic signals in an automobile may be divided loosely into “convenience signals” intended to enhance or simplify the operation of the automobile or make its use more enjoyable, and “required function signals” associated with safety or legally mandated equipment. Whereas the convenience signals may tolerate momentary interruption during low system voltage conditions, the required function signals are less accommodating of interruption and are designed to operate even at low system voltages.
Normally, the cost of providing error-free low-voltage operation is not justified for convenience signals. Nevertheless, because both convenience and required function signals are typically mixed at a single integration hub, manufacturers face the prospect of either providing low voltage compensation circuitry for all types of signals, or accepting occasional erroneous signals from unprotected convenience signals during periods of low system voltage. These spurious signals may produce harmless but false activations of chimes, bulbs, gauges and the like.
BRIEF SUMMARY OF THE INVENTION
The present inventors have recognized that the microcontroller at the integration hub may be enlisted to distinguish between convenience and required function signals and to lock the former against changes during periods of low system voltage without the need for additional circuitry. The microprocessor may monitor the system voltage to detect low system voltage. By “locking” signals from convenience sensors or their input circuits during periods of low system voltage, the last legitimate value of those signals is preserved.
Specifically, the present invention provides an integration hub having connections receiving sensor signals and electrical power from an automotive battery/charger system. A voltage sensor communicates with the connection to the electrical power to provide a measure of the voltage of the electrical power to the sensors. Generally that measure may be a digitized analog value or a single digital bit indicating the relative magnitudes of the voltage and a threshold. A microcontroller evaluates the measure of a voltage to determine whether the voltage is above a predetermined threshold and when it is, employs the sensor signals for control functions and stores the values of the sensor signals. When the measure of the voltage is not above the predetermined threshold, the microcontroller employs the stored values of the previous sensor signals for the control functions.
Thus it is one object of the invention to reduce the effect of erroneous signals from sensors or their input circuits caused by low voltage conditions. Implicit in the present invention is the recognition that the true value of the sensor is likely to be its last value prior to the low voltage condition.
It is another object of the invention to provide a method of reducing the effect of an erroneous signal that may be implemented in a microcontroller without the cost of additional circuitry and yet which may be applied selectively to convenience signals and not to required function signals.
The microcontroller may “debounce” the sensor signals prior to using them for control functions or storing their values. Bounce refers to a condition of a fluctuating state occurring immediately after a change of state of a sensor, typically but not always, associated with mechanical vibration in a set of making and breaking contacts. The debouncing may obtain periodic samples of the sensor signals and test for a predetermined number of successor samples of a consistent value.
Thus it is another object of the invention to provide a system that may be readily integrated with conventional debounce techniques and algorithms.
The microcontroller may initialize the stored values of the sensor signals to predetermined values. The predetermined values may be ones which minimize false actuations under most circumstances.
Thus it is another object of the invention to provide effectively two estimates of the state of signals from convenience sensors that may be used during low system voltage conditions, one estimate based on the last measure of the signal and one default estimate when no measure has yet been determined based on a default signal.
The foregoing and other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessary represent the full scope of the invention, however, and reference must be made to the claims herein for interpreting the scope of the invention.
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Corbin Bradley Jerome
Kanoza Jeffrey Todd
Camby Richard M.
Ford Motor Company
Quarles & Brady LLP
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