Power supply circuit for motor vehicles

A novel vehicle power supply system is suggested which receives its voltage supply from a starter/generator which can be used as a generator in normal operation and as a starter when starting, wherein the starter/generator is connected with a 24 volt ring mains as well as with a 24 volt battery via a pulse inverter and a 300 volt DC intermediate circuit and a bidirectional converter. Additional consumers can be supplied with higher voltages than 24 volts and electric control devices can be supplied with voltage, possible via additional converters, from the bidirectional push-pull converter and the 300 volt DC intermediate network. In addition, this vehicle power supply system contains a plug receptacle with a 220 volt 50 Hz voltage.

BACKGROUND OF THE INVENTION 
The invention relates to a vehicle power supply system comprising a 
battery, a start/generator and a plurality of power consuming devices. 
The production of electrical energy for a motor vehicle power supply system 
is usually effected with a three-phase generator which is connected with a 
voltage regulator. The voltage regulator regulates the generator output 
voltage to the value required for the voltage supply of the vehicle power 
system. Such a motor vehicle power supply system is known e.g. from DE-PS 
33 13 398. Flywheel generators with asynchronous machines or permanently 
excited synchronous machines, which also serve as starters when starting 
and are operated with 12 volts, are known as generators. However, because 
of the low vehicle power supply voltage of approximately 12 volts and the 
low generator output voltage of approximately 12 volts, the designing of 
the machine is quite problematic, since large winding cross-sections are 
required as a result of the high electric current. In addition, high 
losses occur because of the high currents, and large and accordingly 
expensive semiconductor components are simultaneously required in the 
inverters for rectification of the alternating voltage produced in the 
generator and, when star for converting the direct current from the 
battery into an alternating current. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a motor vehicle power supply 
system, in which that the generator output voltage and the input voltage 
of the inverter can be substantially increased. The object of the 
invention is achieved by switching on an additional DC intermediate 
circuit connected between the starter/generator the battery and consuming 
devices. Accordingly, the design of the machine is simplified, and smaller 
winding cross-sections can be used, since the current intensity can be 
kept smaller at a higher voltage. 
In addition, no high losses occur in the power semiconductors used in the 
inverters as a result of the reduced current intensity, i.e. the 
efficiency of the system is improved. Simultaneously, the power 
semiconductors can be reduced and likewise made less expensive 
accordingly. 
Increasing the vehicle power supply from 12 to 24 volts has the advantage 
that the line cross-sections can be reduced. By using a preferably 
bidirectional converter between the vehicle power supply battery and the 
intermediate circuit, additional alternating voltages can be coupled out 
of this converter in a simple manner, e.g. a 220 volt 50 hertz alternating 
voltage can be coupled out which allows the operation of conventional 
electric generators in the vehicle. 
The present invention both as to its construction so to its mode of 
operation, together with additional objects and advantages thereof, will 
be best understood from the following description of the preferred 
embodiments with reference to the accompanying drawings

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The basic arrangement of a vehicle power supply system with asynchronous 
machine 10, a pulse inverter 11 and a bidirectional converter 12 is shown 
in FIG. 1. 
The stator windings 13a, b, c of the asynchronous machine 10 are connected 
in a star connection and are connected to the pulse inverter 11 in such a 
way that each of the stator windings is connected between two pulse 
inverter elements 14 and 15, the other connections of the pulse inverter 
elements are connected with one another so as to be conductive and lead to 
a 300 volt DC intermediate circuit in which a capacitor 16 is connected in 
parallel with the pulse inverter elements 14 and 15. The pulse inverter 
elements comprise transistors and respective recovery diodes. 
The 300 volt DC intermediate circuit is coupled with the 24 volt DC vehicle 
power supply system via a bidirectional converter 12. The 24 volt vehicle 
power supply system comprises only one battery 17 in this basic 
embodiment. 
An embodiment of an asynchronous machine, according to FIG. 1, which is 
connected via a pulse inverter directly with a 12 volt battery 18 as 
flywheel starter/generator, is shown in FIG. 2. For the rest, the 
functioning and manner of operation is analogous to the asynchronous 
machine described in FIG. 1. A permanently excited synchronous machine 
which is constructed e.g. with a two-phase connection or three-phase 
connection and is connected to a battery 18 via inverter and diodes, can 
also be used in principle in place of the asynchronous machine known from 
FIG. 2. A of a permanently excited synchronous machine with a two-phase 
connection 19 is shown in FIG. 3. 
The stator windings 22 and 23 are connected with the negative pole of the 
battery 18 via four semiconductor switches 20a-d which consist of a 
transistor and an antiparallel connected diode; the connection with the 
positive pole of the battery is effected via the four diodes 21a to 21d. A 
Zener diode 22 is connected, in addition, in the connection line between 
the cathodes of these diodes and the positive pole of the battery. The 
positive pole of the battery can be connected directly with the cathodes 
of the diodes 21a to 21d and with the center taps of the windings 22 and 
23 via switches 23, 24 and 25. 
An embodiment example of a complete vehicle power supply configuration with 
multiplex and asynchronous machine as flywheel starter/generator is shown 
in FIG. 4. 
The three phase windings of the asynchronous motor 10 are connected with 
the pulse inverter 11. Another connection line leads from the pulse 
inverter 11 to the bidirectional push-pull converter 26 and further to a 
24 volt ring mains 27 to which regulated and unregulated devices, 29, 30 
and 31 are connected. The consumer devices are connected and regulated via 
controlled power semiconductors 32 and triggered via a data loop 33 
(multiplex). A battery 34 is connected between the output of the 
bidirectional push-pull converter, which is connected with the 24 volt 
consumers devices, and ground. 
An 80 volt 20 kHz voltage for the window heater coupled out of the 
bidirectional push-pull converter 26; the same line is used for the 
voltage supply of the electronic control devices 37 via an AC/DC converter 
36. A DC/AC converter 38 is connected with the output of the flywheel 
starter/generator 10, 11, on one hand, and with one or possibly more 
electronic control devices 37 via the data loop 33, on the other hand. 
Another line leads from this converter to a plug receptacle 39 with 220 
volts and 50 Hz. 
The functioning of the vehicle power supply configuration is explained with 
reference of FIGS. 1 and 4. 
In normal operation, a 300 volt alternating voltage is produced in the 
asynchronous machine 10 which is converted to a 300 volt DC voltage in the 
pulse inverter 11. This 300 volt DC voltage connects to the capacitor 16 
and is chopped on the primary side of the bidirectional converter into a 
high-frequency alternating voltage which is transformed on the secondary 
side to 24 volts and is rectified again. Accordingly, a 24 volt DC voltage 
which is applied to the battery 17 and 34 occurs on the secondary side of 
the bidirectional converter. The 24 volt ring mains and the regulated and 
unregulated 24 volt consumers are supplied with this 24 volt DC voltage 
via a multiplex system. The data loop 33, which connects the individual 
vehicle power supply systems with one another and leads to an electronic 
control device, enables an independent control of the individual systems. 
An additional alternating voltage is coupled out via an additional winding 
on the primary side of the bidirectional push-pull converter, which 
additional alternating voltage directly supplies the window heater. The 
electronic control device 37 is supplied from the same winding via a DC 
voltage converter 36. In addition, a 220 volt, 50 Hz alternating voltage 
is used via another converter 38 for running a plug receptacle 39 in the 
vehicle. 
When starting, the flywheel starter/generator 10, 11 is operated as a 
starter; it is supplied with power from the battery 34 via the 
bidirectional push-pull converter 26 and the pulse inverter 11. Thus, 
either power can be transmitted from the generator into the vehicle power 
supply system and the battery, respectively, or, conversely, power can be 
transmitted from the battery into the starter, when starting, by using the 
bidirectional push-pull converter. 
Individual components can also be used instead of a flywheel 
starter/generator, e.g. a permanently excited preliminary starter designed 
for vehicle power supply voltage and an asynchronous or synchronous 
generator can be used for higher voltage. 
While the invention has been illustrated and described as embodied in a 
motor vehicle power supply circuit, it is not intended to be limited to 
the details shown, since various modifications and structural changes may 
be made without departing in any way from the spirit of the present 
invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapted it for various applications without omitting features 
that, from the standpoint of prior art, fairly constitute essential 
characteristics of the generic of specific aspects of this invention.