Electricity: battery or capacitor charging or discharging – One cell or battery charges another – Vehicle battery charging
Reexamination Certificate
2003-01-24
2004-09-28
Tibbits, Pat (Department: 2838)
Electricity: battery or capacitor charging or discharging
One cell or battery charges another
Vehicle battery charging
Reexamination Certificate
active
06798166
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electrical power supply system for an automobile vehicle.
The electrical power supply for an automobile vehicle is provided using an accumulator battery charged by an alternator, usually driven by a vehicle traction engine.
Most automobile vehicles now use a battery outputting a voltage of 12 V and the corresponding alternator outputs a voltage of 14 V. Since the number of items of equipment consuming electrical energy onboard automobile vehicles is increasing, the power output by the battery also needs to increase. It is becoming quite frequent for each vehicle to be provided with a computer and electrical controls, particularly for the adjustment of seats, assisted braking, suspensions, etc.
The power of a battery with a given voltage (12 V) is proportional to the output current. But an increase in the current also increases the cross section of the power supply cables, which a non-negligible extra cost. This is why the use of accumulator batteries with a higher voltage (36 V) is being considered for the power supply of electrical power sources onboard automobile vehicles. These batteries must be charged at a voltage of 42 V. A voltage of 36 V is high enough to give a substantial power increase without any current increase, and it is also sufficiently low so as not to endanger users.
But in the automobile industry where equipment is produced in large production series, it is difficult to consider changing from one standard to another without a transition, for cost reasons. This is why it is probable that equipment such as lights, computer(s) and small motors will continue to be used with a low voltage (12 V) power supply during a relatively long transition period, and that the high voltage will be used for equipment necessitating more power such as starting, braking, suspensions, etc. Furthermore, for the same cost reasons it would be preferable to be able to continue using low voltage alternators, particularly 14 V, during the transition period, to charge the 12 V and 36 V batteries. Therefore, a circuit is necessary such that the conventional alternator outputting a voltage of 14 V can supply a voltage of 42 V to charge the 36 V battery.
A power supply system for an automobile vehicle has already been proposed by which an alternator outputting a voltage of 14 V could charge a 12 V battery and a 36 V battery. A circuit of this type is shown in FIG.
1
.
This known circuit comprises a battery
10
that outputs a voltage of 12 V, a battery
12
outputting a voltage of 36 V, and a three-phase alternator
14
outputting a voltage of 14 V to charge these two
5
batteries. The alternator is of the claw or Lundell type. In this known circuit, a voltage of 42 V can be applied at the terminals of the battery
12
through a voltage boost circuit, that takes advantage of the high internal inductance in each phase of the alternator
14
. Each phase terminal
14
i
,
14
2
and
14
3
the alternator
14
is connected to the common anode point of a first diode
16
i
to the cathode of a second diode
18
i
, the cathode of the diode
16
i
being connected to the “plus” terminal of the battery
12
and the anode of the diode
18
i
being connected to the “minus” terminal (and therefore the ground) of the same battery
12
outputting a voltage of 36 V. A controlled switch
20
i
installed in parallel on each of the diodes
18
i
.
Furthermore, each phase terminal
14
is connected to
20
the plus terminal of the 12 V battery
10
through another controlled switch
22
i
.
Thus, the circuit shown in
FIG. 2
is obtained for each alternator phase; the alternator
14
supplies power firstly to the battery
10
(12 V) through the inductance
24
i
phase i and the controlled switch
22
i
, and secondly to the battery
12
(36 V) through a diode
16
i
. A switch
20
i
placed between firstly the point common to the inductance
24
i
the anode of the diode
16
i
, and secondly the ground to which the negative terminals of the batteries
10
and
12
and one terminal of the alternator
14
are connected.
Operation is illustrated by the diagrams in
FIGS. 3
a
,
3
b
and
3
c
. The ordinate of the diagram in
FIG. 3
a
represents the intensity I L of the current in the inductance
24
i
, and the abscissa represents the time t, while the diagrams in
FIGS. 3
a
,
3
b
and
3
c
also show the intensity
136
of the charge current of battery
12
(
FIG. 3
b
) and the intensity
1
12
of the charge current of the 12V battery
10
(
FIG. 3
c
)
During a first period with duration &agr;
1
T (
FIG. 3
a
), the switch
20
i
is closed. Under these conditions, the alternator
14
charges inductance
24
i
and the intensity I
L
reaches an intermediate value I
nt
starting from a minimum value I
min
. During a second phase, the switch
20
i
is opened and the switch
22
i
is then closed. Under these conditions, the voltage at the terminal s of battery
10
is the sum of the voltage from this battery and the voltage output by the inductance
24
i
at continues its charge into the battery
10
.
After time &agr;
2
T, the switch
22
i
is open. Under these conditions, the diode
16
i
arts conducting since its anode voltage is greater than the cathode voltage and thus the alternator
14
supplies power to the 36 V battery
12
through the charged inductance
24
i
. The battery
12
is powered until a time T at which the intensity I
L
reaches the value I
min
(
FIG. 3
a
).
BRIEF SUMMARY OF THE INVENTION
The invention is based on the realisation that there are two disadvantages with the circuit shown in FIG.
1
. Firstly this circuit is expensive because two controlled switches have to be supplied per phase and the control is complex. Secondly, there is a period from 0 to &agr;
1
T during each control cycle that is unused for charging either of the batteries.
The invention overcomes these disadvantages.
It relates to an electrical power supply system for a vehicle that comprises a multiphase alternator outputting a given voltage and that will charge a battery with a voltage lower than this given voltage and a battery with a higher voltage. This system comprises a single directional switch for each phase of the alternator through which power is supplied to the low voltage battery, and it is characterised in that the power supply for the battery with a voltage greater than the alternator voltage is not provided with a controlled switch and in that means are provided to control each switch preferably at a frequency significantly greater than the alternator frequency, such that during each control period the switch is closed for a first fraction of the period during which the low voltage battery is charged at the same time that the corresponding phase of the alternator is charged, and is open during a second period during which the higher voltage battery is charged.
With this circuit, only one controlled switch is necessary per phase, and the first fraction of a switch control period is used entirely for charging the lower voltage battery and the second fraction is used entirely for charging the higher voltage battery.
Thus, in general, the invention relates to an electrical power supply system for an automobile vehicle comprising an alternator, a first battery with a voltage less than the electromotive force or the nominal voltage of the alternator, a second battery with a voltage higher than the electromotive force or nominal voltage of the alternator, and control means such that the first battery is charged while the inductance internal to the alternator is being charged and such that the second battery is charged while this internal inductance is being discharged. This system comprises a combination of the following:
for each alternator phase, a controlled switch in series with the first battery with a lower voltage, and a diode means to charge the second higher voltage battery, and
control means for each controlled switch such that
20
when each controlled switch is closed, the first battery is charged at the same time as the inductance of the corresponding ph
Fulbright & Jaworski
Peugeot Citroen Automobiles SA
Tibbits Pat
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