Electrical transmission or interconnection systems – Vehicle mounted systems – Automobile
Reexamination Certificate
1999-04-05
2002-05-21
Paladini, Albert W. (Department: 2836)
Electrical transmission or interconnection systems
Vehicle mounted systems
Automobile
C123S597000, C123S605000
Reexamination Certificate
active
06392315
ABSTRACT:
TECHNICAL FIELD
The present invention concerns automotive electrical systems, and particularly circuits within that system for sensing and utilising an ignition voltage signal. More specifically, the invention concerns a circuit for compensating errors in the sensed ignition voltage signal.
BACKGROUND OF THE INVENTION
Automotive control systems have become progressively more sophisticated. Most new vehicles rely upon many microprocessors or micro controllers for controlling various aspects of the vehicle function. One typical vehicle electrical system
10
as shown in FIG.
1
. The system includes a power supply
11
, which is typically the vehicle battery. A power bus
16
connects the battery to a number of electrical and electronic components. For example, the battery feeds power through the ignition switch
15
, as well as to a power mode controller
17
, and a radio
18
. In addition, ancillary control modules are connected to the power bus
16
, such as a power train control module
20
, an airbag control module
21
, an antilock braking system module
24
, and additional customer supplied modules
22
and
23
.
Each of these components performs various functions in the vehicle control system. For instance, the power mode module
17
is also sometimes referred to as a “body computer” because it controls various active suspension and vehicle body functions. The power train module
20
provides control signals to components within the vehicle power train. The airbag control module
21
, also known as the sensing and diagnostics module, controls the operation of forward and side airbags associated with the vehicle. The ABS module
24
includes a micro controller that provides control signals to the antilock or anti-skid braking system. Finally, the additional modules
22
and
23
can include microprocessors or micro controllers that perform other customer-selected vehicles and/or engine functions.
Although all of the modules within the electrical system
10
are supplied with power directly from the battery
11
, the initiation of these modules can frequently depend upon the ignition state of the vehicle. Most vehicle ignition switches, such as the switch
15
, have many operating positions. For example, the ignition switch
15
can be moved to an IGN
1
position which is activated when the vehicle engine is in the run or crank mode. Alternatively, the ignition switch can be moved to an “accessory position” in which a signal is provided on line
26
. A third possible position for the ignition switch
15
is a “crank” position in which the vehicle engine is being cranked prior to actually starting. In this condition, the ignition switch provides a signal on line
27
that can be used by the power train control module
20
to perform various engine-cranking functions.
In addition to starting the engine, placing the ignition switch
15
in the IGN
1
position also generates a voltage signal on signal line
25
that is used by other electronic modules. Specifically, some of the modules are only activated when the vehicle engine is started and running. When the engine has stopped, these modules can be required to move to a different operating mode.
Thus, as shown at
FIG. 1
, the voltage signal IGN
1
on line
25
is provided to the powertrain control module
20
on line
25
A, the airbag control module
21
on line
25
B, the customer supplied module
23
on line
25
C, the ABS module
24
on line
25
D, and to the power mode module
17
on line
25
E. Each of these modules relies on an accurate voltage for the signal IGN
1
to determine the mode of operation for the particular module. In one specific example, the airbag module control
21
has an active and inactive state. In the active state, the module
21
provides control signals to the airbag components to permit their operation in the event of a vehicle crash. In its inactive state, the module
21
essentially deactivates the airbag system. To insure the safety of the occupants, the airbag control module
21
is in its inactive condition at least until the vehicle engine is running. In order to make this determination; the module
21
reads the signal IGN
1
on signal line
25
B. If that signal exceeds a predetermined threshold voltage, it is assumed that the ignition switch
15
is in its “run/crank” position and that the engine is in fact running.
However, as vehicle electrical systems become more complex, the actual voltage of the ignition signal IGN
1
may be subject to transient fluctuations. It is therefore been necessary to incorporate active circuit components that receive and evaluate the ignition signal IGN
1
to determine the on/off state of the vehicle ignition. In one typical system, a forward biased diode and resistor circuit is utilized to prevent negative transients from affecting the output voltage value. While this resistor-diode network addresses the problem of negative transients, it also introduces a certain degree of non-linearity and unpredictability. Some microcontrollers or electronic modules can handle widely varying ignition voltage signals. However, many other modules are more sensitive and require a more tightly toleranced voltage signal to be evaluated.
There is therefore a need for an ignition sensing system that addresses external transients that impact voltage signal without adding new errors to the output voltage signal.
SUMMARY OF THE INVENTION
In response to this need, the present invention provides a compensation circuit for use with an ignition voltage sensing circuit. The ignition sensing circuit includes an active filter element in series with a resistance element, which is configured to filter or block transients superimposed on the ignition voltage signal. In accordance with the preferred embodiment of the invention, the sensing circuit includes a forward biased diode and a resistor connected between an input receiving the ignition voltage signal and an output node. A second resistor is connected between the output node and ground. Prior to introduction of the inventive compensation circuit, the voltage signal at the output node is provided to a microprocessor of a control device that executes power molding based on the magnitude of the ignition voltage signal.
In accordance with one aspect of the invention, a compensation circuit includes a second active element, such as a diode, in series between the second resistor and ground. In an important feature of the invention, the second active element has substantially identical electrical properties and performance characteristics as the active filter element. In a specific embodiment, both elements constitute substantially identical diodes mounted on a common substrate. Thus, the voltage drop across both diodes is expected to be substantially identical under all environmental conditions, such as temperature.
The present invention capitalizes on the identity in diode performance to compensation for voltage errors in the sensed ignition voltage signal introduced by the active filter element. Thus, in accordance with a further feature of the invention, means are provided for subtracting the voltage drop across the compensation diode from the voltage signal at the first output node of the filter circuit. In the preferred embodiment, this means constitutes software instructions implemented by the microprocessor of the device acting on the ignition voltage signal. These software instructions implement the following equation based on particular values for the two resistors in the filter circuit: IGN
1
=4×(IGN_D
1
−(IGN_D
2
)+2), where IGN
1
is the corrected ignition voltage, IGN_D
1
is the voltage at the first output node, and IGN_D
2
is the voltage at a node between the compensation diode and the second resistor. The corrected ignition voltage value can then be provided to the power moding and testing components of the device microprocessor.
It is one object of the invention to provide an ignition voltage sensing device that can eliminate unnecessary transient signals from the actual ignition voltage. A furthe
Anderson Terrell
Jones Gregory Lynn
Koottungal Paul D.
Peterson Thomas Alton
Delphi Technologies Inc.
Funke Jimmy L.
Paladini Albert W.
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