Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
2002-11-19
2004-10-12
Le, N. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C324S416000, C324S503000
Reexamination Certificate
active
06803768
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for generating a fault signal in a voltage regulator, and corresponding diagnostic circuitry for a system voltage regulator.
The invention also relates to diagnostic circuitry for a system voltage regulator, which circuitry implements the method according to the invention.
The invention relates, particularly but not exclusively, to a method for generating a fault signal in a voltage regulator of an automotive system voltage regulator, the description hereinafter covering this field of application for convenience of illustration only.
2. Description of the Related Art
As is well known, the automotive system voltage regulator
1
basically comprises an alternator
2
, which is connected electrically to a battery
3
and to a voltage regulator
4
, as shown schematically in FIG.
1
.
The alternator
2
comprises a rotor
5
, which is input mechanical torque and power from a car engine. The rotor
5
is commonly referred to as the “field”.
The operation of the system voltage regulator
1
according to the prior art will be briefly reviewed here below.
The voltage regulator
4
detects a system voltage Aplus, and accordingly regulates a field current Iplus flowing through the rotor
5
of the alternator
2
to keep the system voltage Aplus at a constant value.
In particular, the voltage regulator
4
is input the system voltage Aplus, as well as a phase signal PH from the alternator
2
, and has a first output terminal F connected to the rotor
5
and a second output terminal OUT provided to deliver a fault signal Fault.
As shown in
FIG. 1
, the rotor
5
has one end connected directly to the system voltage Aplus, which doubles as a supply voltage reference, and has the other end connected to the output terminal F of the voltage regulator
4
and connected, through the voltage regulator and a controlled switch
6
, to another voltage reference which may be a ground reference GND.
It should be noted that the rotor
5
could be connected the other way around, i.e., with said one end connected to ground GND directly and said other end connected to the system voltage Aplus through a controlled switch. The regulator
1
operation would be the same.
To greatly simplify the system voltage regulator
1
, it can be said that when the demand for current on the alternator
2
increases (e.g., as for a car system, due to a switching on of the car headlights), the field current Iplus flowing through the rotor
5
of the alternator
2
should increase to prevent the system voltage Aplus from falling. Consequently, the torque demand on the engine from the rotor
5
of the alternator
2
also increases.
If the field current Iplus increases rapidly, the demand for torque on the engine rises sharply and may cause the engine to shut down.
In last-generation system voltage regulators, the time constant by which the field current Iplus of the alternator
2
is made to vary changes with engine speed. More precisely, at low RPM, when least torque is output from the engine, the time constant is higher.
A widely used technique for regulating the system voltage Aplus and the field current Iplus in this manner is the pulse-width modulation (PWM) technique, wherein the current Iplus circulated through the rotor
5
is regulated by a fixed-frequency variable duty-cycle drive signal, designated DF in FIG.
1
.
The switch
6
of the voltage regulator
4
is driven by the drive signal DF to regulate the current Iplus flowing in the rotor
5
.
To properly regulate the system voltage Aplus, the up/down variations of the duty cycle of the drive signal DF are provided dependent on the engine speed.
In practice at low engine RPM, the drive signal DF may take a few seconds to go from 0% duty cycle to 100% duty cycle, so that the demand for torque on the engine will increase gradually, rather than sharply, giving the engine control unit plenty of time to respond and avoid an engine shutdown.
Another critical circumstance to the system in question is met at the engine start. To conform with applicable engine emission regulations, the engine control unit is to meter out the fuel such that a substantial number of variables, as read by respective sensors, are satisfied. The system voltage regulator also cumbers engine starting, because its demand of engine torque is unpredictable.
It is on this account that some last-generation system voltage regulators are designed to wait that the engine enters a steady condition, during the engine starting procedure, before the duty cycle value is increased. Accordingly, the voltage regulator
4
is disabled during the engine starting procedure, and the alternator
2
places no demand for torque on the engine while this is being started.
Once the engine starting procedure is completed, the voltage regulator
4
begins to regulate the system voltage after a time delay later referred to as the start-to-regulation delay.
Since an engine is apt to attain steady speed within a few hundreds of milliseconds, this is achieved by simply introducing a delay in the voltage regulator turning-on.
Also, the voltage regulator
4
controls the drive signal DF at a fairly low frequency, i.e., with a definitely low variation time constant of the current flowing through the rotor
5
. This prevents, for instance, a cold engine still running at a low speed from being unintentionally shut down by a sudden demand for power. (For example, a still cold running engine of a car stopped at a traffic light is not put out by the headlights being flashed.)
The voltage regulator
4
of conventional voltage regulators
1
is provided with a diagnostic circuitry
7
adapted to process certain signals from the alternator
2
, e.g., the phase signal PH and the supply voltage Aplus, and to generate the fault signal Fault when the alternator
2
is malfunctioning.
This diagnostic circuitry
7
comprises in particular, as shown schematically in
FIG. 2
, a first logic gate PL
1
, specifically an OR gate, which gate receives on a first input IN
1
the system voltage Aplus and on a second input IN
2
the phase signal PH, and has an output connected to a filter
8
. The filter
8
is to supply the fault signal Fault to an output terminal OUT of the diagnostic circuitry
7
. (The output terminal OUT is the second output terminal of the voltage regulator
4
).
In the diagnostic circuitry
7
, the system voltage Aplus is compared with the phase signal PH: if either signal falls below a given threshold voltage, the diagnostic circuitry
7
issues the fault signal Fault, optionally after a time delay enforced by the filter
8
.
The delay enforced by the filter
8
is dependent on the time constant at which the current in the alternator rotor
5
is varied, and is usually of a few seconds in last-generation regulators. A filter
8
for automotive use comprises basically a large plurality of flip-flops FF and, accordingly, its fabrication requires large silicon area.
In particular, in the system voltage regulator
1
, the voltage regulator
4
exits its standby condition and the fault signal Fault becomes active the moment the engine is started.
The fault signal Fault becomes inactive after the phase voltage PH and system voltage Aplus attain their set values. This event used to take very little time, a few hundred milliseconds, in the old regulators where the rise in rotor current went uncontrolled and the fault signal Fault only stayed active when a failure actually occurred. In last-generation regulators, this same event takes a longer time, so that the signal Fault will stay active longer. In particular, with the engine started and running normally, the signal Fault may stay active for a few more seconds before being disabled.
The following is the visual situation when a car engine in good order and using the diagnostic circuitry
7
shown in
FIG. 2
is started:
the engine starts normally within a few hundred milliseconds; and
a fault light (driven by the fault signal Fault) stays on for a few seconds and then goes off.
To obviate th
Gallinari Maurizio
Maggioni Giampietro
Serratoni Claudio
Iannucci Robert
Jorgenson Lisa K.
Le N.
Seed IP Law Group PLLC
STMicroelectronics S.r.l.
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