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This invention relates to an electrical system for an automotive vehicle
which provides not only the usual low-magnitude DC voltage for energizing
the ordinary low DC voltage loads of the vehicle, but which also provides
a high-magnitude DC voltage capable of energizing a high DC voltage
auxiliary load.
The common motor vehicle electrical system includes a storage battery, a
three-phase AC generator, a three-phase full-wave rectifier, and a voltage
regulator. The battery provides standby power at a DC voltage of
predetermined low magnitude (e.g., a nominal fourteen volts) between a
main power terminal and system ground. The engine driven generator
typically includes output windings across which a three-phase AC voltage
is produced at an amplitude determined by the amount of current fed
through a field winding. The rectifier acts to convert the three-phase AC
voltage to a DC voltage between the main power terminal and system ground
for charging the battery and for supplying the other low-magnitude DC
voltage vehicle loads. The voltage regulator is responsive to the DC
voltage appearing between the main power terminal and system ground to
control the amount of current fed through the field winding of the
generator so as to cause the three-phase AC voltage put out by the output
windings of the generator to have an amplitude correct to establish and
maintain the DC voltage at the predetermined low magnitude.
In a motor vehicle electrical system of the above common type, it is
sometimes necessary or desirable to provide electrical power to an
auxiliary load requiring energization from a DC voltage of substantially
greater magnitude (e.g., 50 to 75 volts) than the low-magnitude DC voltage
ordinarily provided in such system. A high-power windshield heater element
is one example of such a high DC voltage auxiliary load. The present
invention provides a high-magnitude DC voltage power supply applicable to
a motor vehicle electrical system of the above-described type and capable
of advantageously energizing a high DC voltage load such as a high-power
window glass heater.
According to the invention, the foregoing common low-magnitude DC voltage
automotive electrical system is modified by the addition of three
elements: a three-phase AC voltage step-down transformer connected between
the output of the engine driven three-phase generator and the input of the
three-phase full-wave rectifier, a second three-phase full-wave rectifier
connected between the output of the three-phase generator and an auxiliary
power terminal, and a selector switch connected between the auxiliary
power terminal and the main power terminal. In operation, when the switch
is closed, the first rectifier is disabled and the three-phase AC voltage
put out by the generator (as controlled by the voltage regulator) has a
first amplitude correct when rectified by the second rectifier to
establish and maintain the DC voltage between the main power terminal and
system ground at the predetermined low magnitude. Conversely, when the
switch is opened, the first rectifier is enabled and the three-phase AC
voltage put out by the generator (as controlled by the voltage regulator)
has a second higher amplitude correct when stepped down by the transformer
and rectified by the first rectifier to establish and maintain the DC
voltage between the main power terminal and system ground at the
predetermined low magnitude. Additionally, with the switch opened, the
second higher amplitude of the three-phase AC voltage put out by the
generator is also correct when rectified by the second rectifier to
establish and maintain a DC voltage between the auxiliary power terminal
and system ground which is higher than the predetermined low-magnitude DC
voltage by a voltage step-up ratio which is the converse of the voltage
step-down ratio of the transformer. The latter high-magnitude DC voltage
may be applied to energize a high DC voltage accessory load such as a
high-power windshield heater.
In another aspect of the invention, where the voltage regulator is of the
type in which the DC voltage for supplying the field winding of the
generator is derived from a separate rectifier, three further elements are
provided: a second switch operable in unison with the selector switch, and
third and fourth rectifiers. The third rectifier is connected from the
output of the three-phase generator through the second switch to a field
winding supply terminal for rectifying the three-phase AC voltage put out
by the generator to provide a DC voltage of approximately the
predetermined low magnitude for energizing the field winding when the
second switch is closed. The fourth rectifier is connected between the
output of the three-phase transformer and the field winding supply
terminal for rectifying the stepped-down three-phase AC voltage put out by
the transformer to provide a DC voltage of approximately the predetermined
low magnitude for energizing the field winding when the second switch is
opened. In this manner, the field winding of the generator is always
energized by a DC voltage of approximately the predetermined low magnitude
regardless of the state of the selector switch and the amplitude of the
three-phase AC voltage put out by the generator.
The foregoing and other aspects, features and advantages of the invention
may be better understood by reference to the following detailed
description of the preferred embodiments when taken in conjunction with
the accompanying drawings in which:
FIG. 1 is a schematic diagram of one embodiment of the invention.
FIG. 2 is a schematic diagram of a further embodiment of the invention.
Referring to FIG. 1 of the drawing, a motor vehicle electrical system
includes a storage battery 10 connected between a main power terminal 12
and system ground 14 for providing standby power at a DC voltage of
predetermined low magnitude, e.g., a nominal 14 volts. Also connected
between the main power terminal 12 and system ground 14, as represented by
block 16, are various low-magnitude DC voltage loads of the type normally
found in a motor vehicle. It will be understood that each of the loads 16
may include appropriate switches and like devices for controlling the
application of the low-magnitude DC voltage to energize such load.
A three-phase AC generator 20 includes output windings 22a, 22b and 22c and
a field winding 24. Preferably, the generator 20 is of the type where the
phase windings 22a, 22b and 22c are stationary and the field winding 24 is
mechanically driven in rotation by the vehicle engine 26 through an
approximate drive linkage 28. In operation, a three-phase AC voltage is
developed across the output windings 22a, 22b and 22c having an amplitude
determined by the amount of current fed through the field winding 24 and
having a frequency determined by the rotating speed of the field winding
24.
The generator output windings 22a, 22b and 22c are arranged in a wye or
star configuration in which each is connected between a common neutral
node 30 and a different associated one of a set of generator output
terminals 32a, 32b and 32c. As will be appreciated by those skilled in the
art, the line-to-line phase voltage components of the three-phase AC
voltage produced by the generator 20 appear between the respective output
terminals 32a, 32b and 32c. Alternatively, the generator output windings
22a, 22b and 22c could be connected in a delta configuration if desired.
A three-phase voltage step-down transformer 34 includes a set of primary
windings 36a, 36b and 36c, and a corresponding set of secondary windings
38a, 38b and 38c. The transformer primary windings 36a, 36b and 36c are
each connected between different associated pairs of the generator output
terminals 32a, 32b and 32c. The transformer secondary windings 38a, 38b
and 38c are each connected between different associated pairs of
transformer output terminals 40a, 40b and 40c. In operation, the
transformer 34 is effective to step down the amplitude of the three-phase
AC voltage put out by the generator 20 in accordance with a predetermined
voltage step-down ratio, e.g., 4 to 1. Alternatively, the transformer 34
could be an autotransformer.
A first three-phase full-wave bridge rectifier 42 includes positively poled
diodes 44a, 44b and 44c each connected between a different associated one
of the transformer output terminals 40a, 40b and 40c, respectively, and
the main power terminal 12. The first rectifier 42 further includes
negatively poled diodes 46a, 46b and 46c each connected between a
different associated one of the transformer output terminals 40a, 40b and
40c, respectively, and system ground 14. In operation, the first rectifier
42 is effective to rectify the stepped-down three-phase AC voltage put out
by the transformer 34 to provide a first full-wave rectified DC voltage
between the main power terminal 12 and system ground 14, provided that the
rectifier 42 is appropriately forward biased or enabled.
A second three-phase full-wave bridge rectifier 48 includes positively
poled diodes 50a, 50b and 50c each connected between a different
associated one of the generator output terminals 32a, 32b and 32c,
respectively, and an auxiliary power terminal 52. The second rectifier 48
further includes negatively poled diodes 54a, 54b and 54c each connected
between a different associated one of the generator output terminals 32a,
32b and 32c, respectively, and system ground 14. In operation, the second
rectifier 48 is effective to rectify the three-phase AC voltage put out by
the generator 20 to provide a second full-wave rectified DC voltage
between the auxiliary power terminal 52 and system ground 14.
A voltage regulator 56 is responsive to the DC voltage appearing between
the main power terminal 12 and system ground 14 to control the amount of
current fed through the generator field winding 24 to cause the amplitude
of the three-phase AC voltage developed across the generator output
windings 22a, 22b and 22c to be correct to establish and maintain such DC
voltage at the predetermined low magnitude, e.g., a nominal 14 volts. For
this purpose, the voltage regulator 56 may, for example, be of the type
shown in U.S. Pat. No. 3,098,964 or in U.S. patent application No.
775,172.
A selector switch 58, operable between opened and closed states, is
connected between the main power terminal 12 and the auxiliary power
terminal 52. When the switch 58 is closed, the main and auxiliary power
terminals 12 and 52 are connected together. In this condition, the
full-wave rectified DC voltage provided by the second rectifier 48 is
applied through the switch 58 between the main power terminal 12 and
system ground 14. The voltage regulator 56 is responsive to this DC
voltage to control the amount of current fed through the generator field
winding 24 such that the three-phase AC voltage developed across the
generator output windings 22a, 22b and 22c is at a first amplitude correct
when rectified by the second rectifier 48 to establish and maintain the DC
voltage between the main power terminal 12 and system ground 14 at the
predetermined low magnitude, e.g., a nominal 14 volts. Due to the voltage
step-down action of the transformer 34, the positively poled diodes 44a,
44b and 44c of the first rectifier 42 are reverse biased, and so, the
first rectifier 42 is disabled.
When the switch 58 is opened, the main and auxiliary power terminals 12 and
52 are disconnected from each other. In this condition, the positively
poled diodes 44a, 44b and 44c of the first rectifier 42 are forward biased
and the first rectifier 42 is enabled to provide a full-wave rectified DC
voltage between the main power terminal 12 and system ground 14. The
voltage regulator 56 is responsive to this DC voltage to increase the
amount of current fed through the generator field winding 24 such that the
three-phase AC voltage developed across the generator output windings 22a,
22b and 22c is at a second greater amplitude correct when stepped-down by
the transformer 34 and rectified by the first rectifier 42 to establish
and maintain the DC voltage between the main power terminal 12 and system
ground 14 at the predetermined low magnitude.
Further, when the switch 58 is opened, the full-wave rectified DC voltage
provided by the second rectifier 48 is applied between the auxiliary power
terminal 52 and system ground 14. With the three-phase AC voltage put out
by the generator 20 at the second greater amplitude, the DC voltage
appearing between the auxiliary power terminal 52 and system ground 14 is
at a predetermined high magnitude which is greater than the predetermined
low magnitude of the DC voltage appearing between the main power terminal
12 and system ground 14. Specifically, the high-magnitude DC voltage is
greater than the low-magnitude DC voltage by a voltage step-up ratio which
is the converse of the voltage step-down ratio of the transformer 34. For
example, if the voltage step-down ratio of the transformer is 4:1, then
the high-magnitude DC voltage will be approximately four times greater
than the low-magnitude DC voltage, i.e., for a low-magnitude DC voltage of
14 volts, the high-magnitude DC voltage would be approximately 56 volts.
The latter high-magnitude DC voltage may be utilized to energize a high DC
voltage accessory load 60 such as a high-power windshield heater.
FIG. 2 illustrates a further embodiment of the invention applicable where
the voltage regulator 56 is of the type in which the DC voltage for
supplying the field winding 24 of the generator 20 is derived from a
separate rectifier. Examples of this type of voltage regulator are
disclosed in U.S. Pat. Nos. 3,469,168 and 3,539,864. Like numerals are
used to denote like elements in FIGS. 1 and 2.
In addition to the elements shown in FIG. 1, FIG. 2 includes a second
switch 62, and third and fourth three-phase half-wave rectifiers 64 and
66, respectively. The second switch 62 is operated in unison with the
selector switch 58. The third rectifier 64 includes positively poled
diodes 68a, 68b and 68c each connected from a different associated one of
the generator output terminals 32a, 32b and 32c, respectively, through
the second switch 62 to a field winding supply terminal 72 associated with
the voltage regulator 56. The fourth rectifier 66 includes positively
poled diodes 70a, 70b and 70c each connected from a different associated
one of the transformer output terminals 40a, 40b and 40c, respectively, to
the field winding supply terminal 72.
In operation, when the switches 58 and 62 are closed, the third rectifier
64 is effective to rectify the three-phase AC voltage produced at the
generator output terminals 32a, 32b and 32c to provide a DC voltage of
approximately the predetermined low magnitude for energizing the field
winding 24 (with a current determined by the voltage regulator 56).
Further, with the switch 62 closed, the fourth rectifier 66 is reverse
biased or disabled. Alternatively, when the switches 58 and 62 are opened,
the third rectifier 64 is disabled and the fourth rectifier 66 is enabled.
In this condition, the fourth rectifier 66 is effective to rectify the
stepped-down three-phase AC voltage produced at the transformer output
terminals 40a, 40b and 40c to provide a DC voltage of approximately the
predetermined low magnitude for energizing the field winding 24 (with a
current determined by the voltage regulator 56). In this manner, the field
winding 24 is always energized by a DC voltage of approximately the
predetermined low magnitude regardless of the state of the selector switch
58 and the amplitude of the three-phase AC voltage put out by the
generator 20.
It is to be noted that the foregoing embodiments of the invention are
disclosed for purposes of illustration only and are not intended to limit
the invention in any way. As will be appreciated by those skilled in the
art, various alterations and modifications to the illustrated embodiments
may be made without departing from the spirit and scope of the invention.
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