GB2385218A

GB2385218A - Current supply control in a motor vehicle

Info

Publication number: GB2385218A
Application number: GB0223340A
Authority: GB
Inventors: Joachim Schenk
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-10-11
Filing date: 2002-10-08
Publication date: 2003-08-13
Anticipated expiration: 2022-10-08
Also published as: FR2830809A1; FR2830809B1; GB0223340D0; DE10150372A1; GB2385218B

Abstract

An on-board mains supply system for a motor vehicle, particularly a 42 volt supply system, comprises a plurality of loads (V1, V2, V3) each switchable by way of a respective switch (S1, S2, S3) and a generator (G) which serves for current supply of the loads. A control unit (SG) generates switching signals (s1, s2, s3) for the switches and a control signal (i), which influences an excitation current of the generator. Before issue of a switching signal (s1, s2 or s3) for the switches, the control signal (i) reducing the excitation current of the generator is produced. On the basis of this control signal (i), the current led by way of the switches is reduced. This allows use of lower-power switches. This systems may be used in addition to a vehicles 14 volt battery supply.

Description

CURRENT SUPPLY CONTROL IN A MOTOR VEHICLE

The present invention relates to a store-free on-board mains system for a motor vehicle.

In motor vehicles a number of different electrical loads have to be supplied with current.

Some of these loads, for example control apparatus, require a steady supply. Other loads, for example heating devices and fan motors, are not significantly prejudiced in their function in the case of a temporary voltage interruption.

In DE 198 46 319 C1 there is disclosed an energy supply circuit for a motor vehicle on-

board mains with two voltage supply branches which lie at different voltage levels. In that case the first voltage supply branch can be supplied by way of an electrical direct voltage converter from the second voltage supply branch and the second supply branch can be supplied by a generator. In addition, the known energy supply circuit includes a multiple converter with three voltage levels, one inpuVoutput of which is connected with the first voltage supply branch, another inpuVoutput of which is connected with the second voltage supply branch and the third inpuVoutput of which is connected with an energy store associated with the first branch. A decoupling of the supply of the low-voltage mains from the battery terminal voltage can thereby be achieved. This makes it possible to regulate the output voltage of the direct voltage converter, which supplies the mains of a low-

voltage consumer, to a fixed value which corresponds with the discharge voltage of the battery. A narrow tolerance band of the supply voltage can thereby be preset, which simplifies the design of the circuit and, for example, extends the service life of bulbs provided in the on-board mains.

According to the present invention there is provided a store-free part onboard mains system of a motor vehicle, which comprises one or more loads each switchable on and off by way of a respective switch, a generator which is provided for current supply of the loads, and a control apparatus which generates switching signals for the switches and a control signal influencing the excitation current of the generator, wherein the control apparatus before output of a switching signal issues a control signal reducing the excitation current of the generator and the generator on the basis of this control signal reduces the current led by way of the switches.

Preferably, the system is a 42 volt system and preferably the switches are electromechanical and/or electronic switches. For preference the generator on the basis

of the control signal can reduce the current led by way of the switches in such a manner that this corresponds with the operating current or alternatively is smaller than the operating current.

Preferably, the system comprises a further load directly connected with the generator and preferably also an output by way of which a further part on-board mains can be supplied with current. In addition, the system can have an own reference potential with which the generator and the loads are connected. Preferably it includes an output by way of which a further part on-board mains, which similarly has the reference potential, can be supplied with current.

In a preferred embodiment the generator is a 42 volt generator, the output is connected with a 14 volt on-board mains and in the case of non- active loads the 42 volt generator regulated to 14 volts is provided for supporting the supply of the 14 volt on-board mains.

The. invention may make it possible to realise a store-free part on-board mains in economic manner, in particular by permitting use of poweroptimised and thereby cost-

optimised standard components, particularly switches. Through reduction in the current, which is conducted by way of the switches, before a switching process the switches do not have to be designed for the maximum switch-on current of the loads. This saves costs, constructional space, weight and power loss. Higher currents only have to be conducted by way of closed switches, switching processes in the presence of higher currents being avoided. If the on-board mains system is a 42 volt system provided in the vehicle additionally to a 14 volt system, consumers with a higher current need can be supplied. In addition, if a load is present which has to be constantly supplied, then this load can be directly connected with the generator otherwise than via a switch. This allows control or regulation of the supply of this load directly by way of the excitation circuit, i.e. through presetting a suitable control signal for setting an associated excitation current in the generator.

If the energy requirement in the on-board mains system is temporarily reduced, then in advantageous manner energy for a further on-board mains system can be made available at an output of the part on-board mains.

Through separation of the normal vehicle earth from a reference potential of the on-board mains system, a cost-intensive short-circuit protection between the systems which are present can be dispensed with. This can be achieved by connection of the reference potential with the consumers of the on-board mains system and the generator of that system by way of an additional cable, this connection being insulated from the normal vehicle earth.

Embodiments of the invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a block circuit diagram of a first on-board mains system embodying the invention; and Fig. 2 is a block circuit diagram of a second on-board mains system embodying the invention.

Referring now to the drawings there is shown in Fig. 1 a store-free part on-board mains system of a motor vehicle, preferably a 42 volt on-board mains. This is provided in the vehicle additionally to a 14 volt on-board mains, which is not illustrated and which forms a second part on-board mains of the motor vehicle. The 42 volt on-board mains is provided for supply of loads or consumers of high power and/or higher operating voltage, these being denoted by V1, V2, V3 and V4.

The loads V1, V2, V3 are each connected by way of a respective switch S1, S2, S3 to a 42 volt generator G. which is provided for power supply of the loads; the term generator signifies current-generating means of any appropriate kind and in motor vehicles usually has the form of an alternator. The stated switches are electromechanical switches, electronic switches or partly electromechanical and partly electronic switches.

The control of the switching-on and switching-off processes of the switches S1, S2, S3 is carried out with use of switching signals s1, s2, s3 which are produced in a control unit SG. The control unit SO, in addition, produces a control signal i which is fed to the generator G. This control signal i influences the excitation current of the generator and thus the current led by way of the switches S1, S2, S3 to the loads.

If one or more of the loads is or are to be switched on or switched off, then the control unit SO, before issue of the switching signal or switching signals, issues a control signal reducing the excitation current of the generator. This has the consequence that also the current led by way of the switches to the loads is reduced.

In a first form of the 42 volt mains the current led by way of the switches is reduced in such a manner that it corresponds with the operating current of the loads. In a second form the current led by way of the switches is further reduced so that it is smaller than the operating current of the loads.

In both forms the switches used do not have to be designed for the maximum switch-on current of the loads, since all switching processes take place at substantially lower currents. This enables a saving of costs, constructional space, weight and loss power.

The initial blocking currents of motors, cold currents of heaters and lamps, etc., are thus limited by a suitable influencing of the excitation current of the generator G. The more the on-board mains voltage or current led by way of the switches is reduced before a switching process, the greater the extent to which lower power electromechanical switches can be used. Such low-power electromechanical switches can, due to burning of the contacts on opening and closing of the contacts, switch only a fraction of the current which can be conducted when the contacts are closed. Due to the described reduction in the current, which is conducted by way of the switches, before a switching process, low-

power electromechanical switches can be used, since higher currents do not flow at the instant of switching.

In a development, the on-board mains also has a load V4 which has to be constantly supplied with current. This load is directly connected with the generator G without use of a switch. Control or regulation of the supply of this load V4 is effected directly by way of the excitation circuit, i.e. through a suitable presetting of a control signal i, which influences the excitation current of the generator G. by the control unit SO.

A further development consists in providing an output connection A by way of which, in the case of a temporarily reduced 42 volt energy requirement' energy is supplied to the 14 volt on-board mains which is additionally present in the vehicle. This output connection A is

connected by way of a switch S4 with the generator G. A switch control signal s4 for this switch S4 is similarly produced by the control unit SG.

In a second embodiment, which is illustrated in Fig. 2, a reference potential BP of the 42 volt on-board mains can be separated from the normal vehicle earth. In this case it is possible to dispense with a costly short-circuit protection between the different on-board mains of the vehicle. In this second embodiment the generator G and the loads V1, V2, V3 and V4 are connected, with use of an additional cabling, with the stated reference potential BP, which is isolated from the normal vehicle earth.

The arrangement described in the foregoing allows an economic realization of a multi-

voltage on-board mains. In particular, the introduction of a 42 volt onboard mains as a

supplement to a 14 volt on-board mains is attractive in economic terms. This applies particularly to inclusion of a 42 volt on-board mains in a small vehicle.

Claims

1. A store-free on-board mains system for a motor vehicle, comprising current-

generating means for generating current to operate at least one load, a respective switch for switching the or each load on and off, control means for providing a switch control signal to control the or each switch and a current-generation control signal to influence an excitation current of the current generating means, the control means being arranged to provide, before provision of a switch control signal for the switch or one of the switches, a current-generation control signal to cause reduction in the excitation current and consequently to cause the current- generating means to reduce the current conducted by way of that switch.

2. A system as claimed in claim 1, wherein the system is a 42 volt system.

3. A system as claimed in claim 1 or claim 2, wherein the switch or at least one of the switches is an electromechanical or electronic switch.

4. A system as claimed in any one of the preceding claims, wherein the current-

generating means is responsive to the current-generation control signal to reduce the current conducted by the switch or one of the switches to correspond with the operating current of the associated load.

5. A system as claimed in any one of claims 1 to 3, wherein the currentgenerating means is responsive to the current-generation control signal to reduce the current conducted by the switch or one of the switches to below the operating current of the associated load.

6. A system as claimed in any one of the preceding claims, comprising means for connecting a further load directly with the current-generating means.

7. A system as claimed in any one of the preceding claims, comprising an output connectible with a further on-board mains system.

8. A system as claimed in any one of the preceding claims, comprising an own reference potential connected with the current-generating means and connectible with the or each load

9. A system as claimed in claim 8, when appended to claim 7, wherein the further on-

board mains system has the same reference potential.

10. A system as claimed in claim 7, wherein the current-generating means is a 42 volt generator or alternator, the further on-board mains system is a 14 volt system and the current-generating means is regulable to 14 volts when the or each load is inactive and supplies the further system with supporting current.